Antiparkinsonian Drugs

Parkinson's Disease (Antiparkinsonian Drugs)

1. Definition & overview

• Parkinsonism — an extrapyramidal motor disorder defined by the tetrad of rigidity, tremor, hypokinesia/bradykinesia, and postural instability, with secondary defective posture/gait, mask-like face, and sialorrhoea. (KDT 8e Ch.31, p.452)
• Bradykinesia — must be present for a diagnosis of Parkinson's disease; focal dystonic features may also be present. (Katzung 16e Ch.28, p.518)
• Pathological hallmark — loss of pigmented dopaminergic neurones of the substantia nigra pars compacta (SN-PC) with intracellular Lewy bodies. (G&G 14e Ch.21, p.413)
• Lewy bodies — intracellular inclusions whose principal aggregated component is α-synuclein; PD is now recognised as a synucleinopathy. (G&G 14e Ch.21, p.414)
• Threshold for symptoms — loss of 70–80 % of DA-containing SN-PC neurones accompanies symptomatic PD. (G&G 14e Ch.21, p.415)
• Natural history — untreated PD progresses over 5–10 years to a rigid, akinetic state; death usually from aspiration pneumonia or pulmonary embolism. (Katzung 16e Ch.28, p.518)
• Pharmacotherapy impact — drugs do not change the underlying course but provide ~5–10 years of additional productive life and lower mortality when initiated early. (KDT 8e Ch.31, p.460; G&G 14e Ch.21, p.415)
• Wilson's disease — (hepatolenticular degeneration; chronic copper poisoning) is a rare cause of parkinsonism. (KDT 8e Ch.31, p.452)
• Drug-induced parkinsonism — (reversible) due to neuroleptics and metoclopramide (D₂ blockers) is now common; reserpine-induced (DA depleter) is historical. (KDT 8e Ch.31, p.452)

2. Non-motor manifestations

• Wider involvement — PD affects brainstem, hippocampus, neocortex beyond the dopaminergic system. (G&G 14e Ch.21, p.415)
• Premotor (preclinical) — hyposmia/anosmia, REM-sleep behaviour disorder, constipation, depression, anxiety — may precede motor symptoms by years. (G&G 14e Ch.21, p.415; Katzung 16e Ch.28, p.518)
• Cognitive features — impaired attention, hallucinations, delusions, executive and visuospatial dysfunction; dementia accompanies advanced disease. (G&G 14e Ch.21, p.415)
• Autonomic dysfunction — sphincter or sexual dysfunction, dysphagia/choking, sweating abnormalities, sialorrhoea, BP dysregulation. (Katzung 16e Ch.28, p.518)
• Affective symptoms — anxiety, depression, apathy, fatigue; sensory complaints and pain are recognised non-motor features. (Katzung 16e Ch.28, p.518)
• Braak staging — stage 1 olfactory bulb/medulla → stage 2 pons → stage 3 midbrain (incl. SN-PC, motor symptoms emerge) → stage 4 mesocortex/thalamus → stages 5–6 neocortex. (Katzung 16e Ch.28, p.519)

3. Pathogenesis & etiology

• Multifactorial cause — ageing + genetic predisposition + oxidative free-radical generation + environmental MPTP-like toxins + excitotoxic NMDA-mediated Ca²⁺ overload. (KDT 8e Ch.31, p.452)
• Pathogenic mechanisms — impaired protein degradation, intracellular protein accumulation, oxidative stress, mitochondrial damage, inflammatory cascades, apoptosis. (Katzung 16e Ch.28, p.518)
• Twin studies — genetic factors are most important when PD presents under age 50. (Katzung 16e Ch.28, p.518)
• Genetic abnormalities — account for 10–15 % of PD cases. (Katzung 16e Ch.28, p.518)
• Autosomal-dominant genes — SNCA (α-synuclein, 4q21) — point mutations or duplication/triplication; LRRK2 (12cen) — most common AD form, gain-of-kinase function; UCHL1. (Katzung 16e Ch.28, p.518; G&G 14e Ch.21, p.413)
• Autosomal-recessive (early-onset) — PARK2/Parkin (E3 ubiquitin ligase loss-of-function); DJ-1 and PINK1 (mitochondrial quality-control proteins). (Katzung 16e Ch.28, p.518; G&G 14e Ch.21, p.413)
• Risk-modifier genes — α-synuclein, LRRK2, MAPT (tau), GBA (β-glucocerebrosidase). (G&G 14e Ch.21, p.413)
• GBA mutations — heterozygous GBA mutations are the strongest single common genetic risk factor for PD; not in KDT. (G&G 14e Ch.21, p.414)
• Protective epidemiologic factors — cigarette smoking, coffee, anti-inflammatory drug use, high serum uric acid. (Katzung 16e Ch.28, p.518)
• Risk factors — teaching, healthcare, farming professions; lead or manganese exposure; vitamin D deficiency; pesticide exposure. (Katzung 16e Ch.28, p.518; G&G 14e Ch.21, p.414)
• MPTP — 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine — a protoxin that opened the field of PD experimental models in 1983. (Katzung 16e Ch.28, p.530)
• MPTP mechanism — MPTP → (MAO-B oxidation) → MPP⁺; MPP⁺ concentrated in SN-PC neurones via DAT; inhibits mitochondrial complex I → halts oxidative phosphorylation → cell death → striatal DA depletion → severe parkinsonism. (Katzung 16e Ch.28, p.530)
• Selegiline rationale — prophylactic MAO-B inhibition prevents MPTP → MPP⁺ conversion and protects animals — basis for trials of selegiline/rasagiline as putative neuroprotective agents. (Katzung 16e Ch.28, p.530)
• Prion-like spread — Lewy bodies in fetal dopaminergic transplants placed years earlier support the hypothesis that PD may behave as a prion-like spreading proteinopathy. (Katzung 16e Ch.28, p.518)
• α-Synuclein SAA — spinal-fluid seed amplification assay has high sensitivity/specificity for distinguishing PD from controls and may serve as a pre-symptomatic biomarker. (Katzung 16e Ch.28, p.528)

4. Neurochemistry — dopamine system

• Core lesion — degeneration of the nigrostriatal (dopaminergic) tract from SN-PC → DA deficiency in striatum which controls muscle tone and coordinates movement. (KDT 8e Ch.31, p.452)
• DA imbalance hypothesis — loss of inhibitory dopaminergic input creates an imbalance between dopaminergic (inhibitory) and cholinergic (excitatory) systems in the striatum; cholinergic system is not primarily affected but its suppression by anticholinergics restores balance. (KDT 8e Ch.31, p.452)
• DA receptor subtypes — five (D₁–D₅), all GPCRs, two families. (KDT 8e Ch.31, p.453; G&G 14e Ch.21, p.415)
• D₁-like family (D₁, D₅) — excitatory; G_s-coupled → ↑ adenylyl cyclase → ↑ cAMP; also ↑ PIP₂ hydrolysis → ↑ intracellular Ca²⁺ + PKC via IP₃ and DAG. (KDT 8e Ch.31, p.453)
• D₂-like family (D₂, D₃, D₄) — inhibitory; Gᵢ-coupled → ↓ adenylyl cyclase, open K⁺ channels, depress voltage-sensitive Ca²⁺ channels. (KDT 8e Ch.31, p.453)
• Receptor distribution — D₁ + D₂ both abundant in striatum (most relevant to PD therapy); D₂ in SN-PC and pituitary mammotropes; D₃ in nucleus accumbens and hypothalamus; D₄, D₅ mostly in neocortex, midbrain, medulla, hippocampus. (G&G 14e Ch.21, p.415; KDT 8e Ch.31, p.453)
• Both D₁ and D₂ — involved in the therapeutic response to levodopa despite opposite cellular effects, because they regulate two pathways with opposite effects on thalamocortical drive. (KDT 8e Ch.31, p.453)
• Therapeutic relevance — antiparkinsonian benefit appears mostly D₂-mediated, but D₁ stimulation may be required for maximal benefit. (Katzung 16e Ch.28, p.519)
• D₃-selective agonists — (pramipexole) developed; D₃ implicated in mood and impulse-control behaviours of DA agonist therapy. (Katzung 16e Ch.28, p.524)
• DA synthesis — phenylalanine → (PAH, hepatic) → tyrosine → (TH, rate-limiting) → l-DOPA → (AADC) → dopamine → vesicles via VMAT2. (G&G 14e Ch.21, p.416)
• DA metabolism — synaptic DA → DAT/NET reuptake or postsynaptic OCT3 → cytosolic DA → MAO + ALDH (intraneuronal) and COMT + MAO/ALDH (non-neuronal) → final metabolite HVA. (G&G 14e Ch.21, p.416)
• Other neurotransmitters — noradrenaline and serotonin also reduced in PD brain — clinical relevance uncertain. (Katzung 16e Ch.28, p.519)

5. Basal-ganglia circuitry & pathophysiology of motor symptoms

• Modulatory side-loop — basal ganglia regulate flow of information from cerebral cortex to spinal motor neurones; striatum (caudate + putamen) is the principal input structure. (G&G 14e Ch.21, p.415; KDT 8e Ch.31, p.453)
• Striatal cells — projection neurones are GABAergic medium spiny neurones; small but important interneurones use acetylcholine and neuropeptides. (G&G 14e Ch.21, p.415)
• Striatal inputs — excitatory glutamatergic from motor cortex; modulatory dopaminergic from SN-PC; balancing cholinergic interneurones. (KDT 8e Ch.31, p.453)
• Direct pathway — striatum → SN-PR / GP-I (single GABAergic inhibitory link); striatal neurones express excitatory D₁ receptors. (KDT 8e Ch.31, p.454; G&G 14e Ch.21, p.415)
• Indirect pathway — striatum → GP-E → STN → SN-PR / GP-I; two GABAergic inhibitory relays + one excitatory glutamatergic terminal from STN; striatal neurones express inhibitory D₂ receptors. (KDT 8e Ch.31, p.454; G&G 14e Ch.21, p.415)
• Output — SN-PR + GP-I are GABAergic → VA/VL thalamus → glutamatergic feedback to motor cortex. (G&G 14e Ch.21, p.415)
• Net effect of striatal DA — stimulates D₁-direct pathway → ↑ inhibition of SN-PR/GP-I → disinhibits thalamus → ↑ cortical drive; inhibits D₂-indirect pathway → ↓ STN drive → ↓ SN-PR/GP-I → again disinhibits thalamus. Both pathways converge to facilitate movement and reduce muscle tone. (KDT 8e Ch.31, p.454; Katzung 16e Ch.28, p.519)
• In PD — loss of nigrostriatal DA → ↓ direct-pathway activity + ↑ indirect-pathway activity → ↑ inhibitory output from SN-PR/GP-I → ↓ thalamocortical drive → bradykinesia. (G&G 14e Ch.21, p.415)
• Model limitations — does not adequately explain rest tremor or levodopa-induced dyskinesia; anatomy is more complex with multiple co-transmitters. (G&G 14e Ch.21, p.415)
• Surgical-target rationale — model predicts that lesioning or stimulating STN or GP-I should reduce excessive inhibitory output and restore motor function — borne out by DBS results. (Katzung 16e Ch.28, p.527)

6. Classification of antiparkinsonian drugs

Drugs affecting brain dopaminergic system

• DA precursor — Levodopa.
• Peripheral decarboxylase inhibitors (adjuvants) — Carbidopa, Benserazide.
• Dopaminergic agonists — ergot derivatives — Bromocriptine, Pergolide.
• Non-ergot oral — Pramipexole, Ropinirole.
• Non-ergot transdermal — Rotigotine.
• Non-ergot injectable (rescue) — Apomorphine.
• MAO-B inhibitors — Selegiline, Rasagiline, Safinamide.
• COMT inhibitors — Entacapone, Tolcapone, Opicapone.
• NMDA antagonist / DA facilitator — Amantadine.
• Adenosine A₂A receptor antagonist — Istradefylline.

Drugs affecting brain cholinergic system

• Central anticholinergics — Trihexyphenidyl (benzhexol), Procyclidine, Biperiden, Benztropine.
• Antihistaminics with central anticholinergic action — Orphenadrine, Promethazine, Diphenhydramine. (KDT 8e Ch.31, p.453)

7. Levodopa — overview & mechanism

• Chemical identity — (–)-3-(3,4-dihydroxyphenyl)-l-alanine — levorotatory stereoisomer of dopa, immediate metabolic precursor of DA. (G&G 14e Ch.21, p.415)
• Most efficacious single agent — in PD; efficacy exceeds any other antiparkinsonian drug used alone. (KDT 8e Ch.31, p.452)
• 1967 breakthrough — Cotzias produced dramatic improvement based on prior work showing DA depletion in PD striatum and reversal of reserpine-induced motor defect by DOPA. (KDT 8e Ch.31, p.452)
• Why not give DA directly — DA does not cross BBB; levodopa crosses via L-aromatic amino acid transporter (LAT). (G&G 14e Ch.21, p.415; KDT 8e Ch.31, p.452)
• Fate without DDC inhibitor — >95 % decarboxylated peripherally (gut + liver); only 1–2 % crosses BBB (KDT) / 1–3 % (G&G/Katzung) — minor numerical disagreement; figure is approximate. (KDT 8e Ch.31, p.452; G&G 14e Ch.21, p.415)
• Sites of peripheral DA action — heart, vessels, peripheral organs, CTZ (the chemoreceptor trigger zone is in floor of IV ventricle but is outside BBB). (KDT 8e Ch.31, p.453)
• Central conversion — levodopa entering brain is taken up by surviving dopaminergic neurones, decarboxylated to DA, stored in vesicles, and released as transmitter. (KDT 8e Ch.31, p.453)
• Buffering capacity — surviving terminals essential for stable benefit — they buffer rapid changes in plasma levodopa; loss of buffering drives motor fluctuations. (G&G 14e Ch.21, p.416)

8. Levodopa — pharmacological actions

8.1 CNS

• Selective effect — little effect in normal individuals or in non-PD neurological disease — selectively reverses the deficit in PD. (KDT 8e Ch.31, p.453)
• Order of improvement — hypokinesia and rigidity first, tremor later; secondary symptoms (posture, gait, handwriting, speech, facial expression, mood, self-care) gradually normalised. (KDT 8e Ch.31, p.453)
• Therapeutic ceiling — benefit nearly complete in early disease but declines as disease advances. (KDT 8e Ch.31, p.453)
• Dementia — if present, does not improve with levodopa and predisposes to psychiatric symptoms. (KDT 8e Ch.31, p.453)

8.2 CVS

• Tachycardia — from peripheral DA via β-adrenergic action. (KDT 8e Ch.31, p.454)
• BP not raised — despite vascular adrenergic stimulation — instead postural hypotension is common (probable central action: ↓ sympathetic outflow from excess central DA/NA). (KDT 8e Ch.31, p.454)
• Ganglionic effect — peripheral DA in autonomic ganglia may impede ganglionic transmission. (KDT 8e Ch.31, p.454)
• Tolerance — develops to both cardiac stimulant and hypotensive actions. (KDT 8e Ch.31, p.454)
• Arrhythmias — tachycardia, ventricular extrasystoles, rarely atrial fibrillation; incidence low and reduced further by carbidopa coadministration. (Katzung 16e Ch.28, p.521)

8.3 CTZ

• Nausea / vomiting — DA is excitatory at CTZ → nausea and vomiting in ~80 % on levodopa monotherapy; tolerance develops gradually. (KDT 8e Ch.31, p.454; Katzung 16e Ch.28, p.520)
• With carbidopa — incidence falls to <20 %. (Katzung 16e Ch.28, p.521)

8.4 Endocrine

• Prolactin — DA acts on pituitary mammotropes → ↓ serum prolactin during levodopa therapy. (KDT 8e Ch.31, p.454)
• GH — ↑ GH release in normals; GH is not increased in parkinsonian patients — regulation appears altered. (KDT 8e Ch.31, p.454)

9. Levodopa — pharmacokinetics

• Absorption — rapid from small intestine via active transport for aromatic amino acids. (KDT 8e Ch.31, p.455; G&G 14e Ch.21, p.415)
• Bioavailability — gastric emptying — slow emptying ↑ exposure to gut-wall + hepatic degrading enzymes → less reaches BBB. (KDT 8e Ch.31, p.455)
• Bioavailability — gastric pH — affects absorption. (Katzung 16e Ch.28, p.520)
• Dietary amino acids — compete with levodopa for the same carrier — blood levels lower with high-protein meals; the same carrier limits BBB transport. (KDT 8e Ch.31, p.455; G&G 14e Ch.21, p.416)
• T_max — peak plasma 0.5–2 h after oral dose. (Katzung 16e Ch.28, p.520; G&G 14e Ch.21, p.416)
• Plasma t½ — 1–2 h (KDT) / 1–3 h (Katzung & G&G); inter-individual variability is wide. (KDT 8e Ch.31, p.455; Katzung 16e Ch.28, p.520)
• Pyridoxal — cofactor for dopa decarboxylase — explains pyridoxine interaction. (KDT 8e Ch.31, p.455)
• Excretion — ~⅔ of dose appears in urine as metabolites within 8 h, mainly HVA and DOPAC after conjugation. (Katzung 16e Ch.28, p.520; KDT 8e Ch.31, p.455)
• Periphery — levodopa ⇌ 3-O-methyldopa (3-OMD via COMT); levodopa → DA via DDC → DOPAC (MAO/ALDH) → HVA (COMT). (KDT 8e Ch.31, p.455)
• Brain — 3-OMD via COMT; levodopa → DA via DDC; DA → 3-MT (COMT) and DOPAC (MAO-B/ALDH) → both → HVA. (KDT 8e Ch.31, p.455)
• 3-OMD competition — high 3-OMD levels reduce levodopa entry by competing for active BBB transport. (Katzung 16e Ch.28, p.526)

10. Levodopa — adverse effects

10.1 At initiation (early, dose-related, reversible)

• Nausea & vomiting — in nearly every patient on monotherapy (~80 %); minimised by starting low, dividing doses, taking with meals; tolerance develops. (KDT 8e Ch.31, p.455; Katzung 16e Ch.28, p.520)
• Postural hypotension — in ~⅓; mostly asymptomatic; some experience dizziness or syncope; worse with antihypertensives; tolerance develops. (KDT 8e Ch.31, p.455)
• Cardiac arrhythmias — β-adrenergic action of peripheral DA; more in pre-existing heart disease. (KDT 8e Ch.31, p.456)
• Angina — exacerbation in patients with pre-existing ischaemic heart disease. (KDT 8e Ch.31, p.456)
• Taste alteration — may occur. (KDT 8e Ch.31, p.456)
• Hypertension — with massive doses, with non-selective MAOIs, or with sympathomimetics. (Katzung 16e Ch.28, p.522)

10.2 With prolonged therapy — motor complications

• Dyskinesias — abnormal involuntary movements — facial tics, grimacing, tongue thrusting, choreoathetoid limb movements. (KDT 8e Ch.31, p.456)
• Incidence — up to 80 % of patients receiving levodopa for >10 years. (Katzung 16e Ch.28, p.522)
• Onset — after a few months at therapeutic dose; intensity correlates with plasma levodopa levels; no tolerance develops. (KDT 8e Ch.31, p.456)
• Phenotype — choreoathetosis of face and distal extremities is most common; pattern tends to be constant within an individual. (Katzung 16e Ch.28, p.522)
• Pathogenesis — unclear; hypotheses include unequal striatal DA distribution and dopaminergic denervation + chronic pulsatile receptor stimulation. (Katzung 16e Ch.28, p.522)
• Continuous delivery — lower incidence with intraduodenal/intrajejunal infusion or transdermal patch — supports the pulsatile-stimulation hypothesis. (Katzung 16e Ch.28, p.522)
• Diphasic dyskinesias — occur as patient comes on and again as benefit wears off; managed by smaller, more frequent doses or substituting some levodopa with a DA agonist. (Katzung 16e Ch.28, p.522)

10.3 Response fluctuations

• Wearing-off — end-of-dose deterioration: gradual loss of benefit before next dose; progresses with disease. (KDT 8e Ch.31, p.456)
• On–off phenomenon — rapid, unpredictable switches between mobility (on) and akinesia (off), often with dyskinesia during on-state. (KDT 8e Ch.31, p.456)
• All-or-none — develops over years — patient alternately well and disabled; abnormal movements may jeopardise even the on-phase. (KDT 8e Ch.31, p.456)
• Mechanism — progressive degeneration of DA neurones with loss of buffering capacity → moment-to-moment striatal DA synthesis is unstable. (KDT 8e Ch.31, p.456)
• Management strategies — dose fractionation, more frequent dosing, evening protein meal, longer-acting / controlled-release formulations, COMT inhibitors, MAO-B inhibitors, DA agonists, apomorphine rescue, inhaled levodopa, surgery. (Katzung 16e Ch.28, p.522)

10.4 Behavioural / psychiatric

• Spectrum — mild anxiety, nightmares to severe depression, mania, hallucinations, mental confusion, frank psychosis. (KDT 8e Ch.31, p.456)
• Mechanism — excessive DA action in limbic system (antidopaminergics are antipsychotic). (KDT 8e Ch.31, p.456)
• With carbidopa — more common (higher central levels); may be precipitated by intercurrent illness or surgery. (Katzung 16e Ch.28, p.522)
• Contraindication — levodopa is contraindicated in patients with psychotic illness. (KDT 8e Ch.31, p.456)
• More likely culprits — confusion and hallucinations developing in PD patients are more likely due to anticholinergics, amantadine, or DA agonists than to levodopa itself. (Katzung 16e Ch.28, p.522)
• Dopamine dysregulation syndrome — compulsive overuse of dopaminergic medication + other impulsive behaviours; more common with DA agonists. (Katzung 16e Ch.28, p.522)
• Punding — stereotyped, complex but purposeless motor activity (sorting/lining objects, repetitive grooming); responds to dose reduction or atypical antipsychotics. (Katzung 16e Ch.28, p.522)
• Atypical antipsychotics of choice — low D₂ affinity — clozapine, quetiapine, olanzapine, risperidone; clozapine and quetiapine considered most effective and best tolerated. (Katzung 16e Ch.28, p.522; G&G 14e Ch.21, p.418)
• Pimavanserin — selective serotonin 5-HT_2a inverse agonist 34 mg/day; FDA-approved for PD psychosis; avoid in QT prolongation; contraindicated for dementia-related psychosis. (Katzung 16e Ch.28, p.522)
• Black-box warning — increased mortality in elderly with dementia-related psychosis treated with antipsychotics. (G&G 14e Ch.21, p.421)
• Suicidality — appears increased in PD; whether disease- or treatment-related is uncertain. (G&G 14e Ch.21, p.418)
• Conventional D₂ blockers — phenothiazines, haloperidol — contraindicated; worsen parkinsonism. (G&G 14e Ch.21, p.418)

10.5 Miscellaneous adverse effects

• Mydriasis — may precipitate acute angle-closure glaucoma in susceptible eyes. (Katzung 16e Ch.28, p.522)
• Various — blood dyscrasias; positive Coombs' test with haemolysis; hot flushes; aggravation of gout; abnormalities of smell or taste. (Katzung 16e Ch.28, p.522)
• Discoloration — brownish saliva, urine, vaginal secretions. (Katzung 16e Ch.28, p.522)
• Other — priapism (rare); transient ↑ blood urea, transaminases, alkaline phosphatase, bilirubin. (Katzung 16e Ch.28, p.522)

10.6 Cautions / contraindications

• Cautious use — elderly; ischaemic heart disease, cerebrovascular disease, psychiatric illness, hepatic and renal disease, peptic ulcer (bleeding risk), glaucoma, gout. (KDT 8e Ch.31, p.456)
• Contraindicated — angle-closure glaucoma, active psychosis, history of melanoma or suspicious skin lesions (levodopa is a precursor of melanin and may theoretically activate melanoma). (Katzung 16e Ch.28, p.523)
• Open-angle glaucoma — acceptable if IOP is controlled and monitored. (Katzung 16e Ch.28, p.523)
• Drug holidays — (3–21-day discontinuation) no longer recommended — risks of aspiration pneumonia, VTE, depression; benefit temporary. (KDT 8e Ch.31, p.461; Katzung 16e Ch.28, p.522)
• Abrupt withdrawal — of levodopa or DA agonists may precipitate a state resembling neuroleptic malignant syndrome with rigidity, hyperthermia, mental deterioration. (KDT 8e Ch.31, p.461; Katzung 16e Ch.28, p.525)

11. Levodopa — drug interactions

• Pyridoxine (B₆) — abolishes the therapeutic effect of levodopa monotherapy by enhancing peripheral decarboxylation; does NOT abolish effect when carbidopa coadministered. (KDT 8e Ch.31, p.456; G&G 14e Ch.21, p.420)
• Phenothiazines, butyrophenones, metoclopramide — reverse therapeutic effect by blocking D₂ receptors; antiemetics of these classes should be avoided. (KDT 8e Ch.31, p.456)
• Domperidone — blocks levodopa-induced nausea/vomiting WITHOUT abolishing antiparkinsonian effect because it does not cross BBB but reaches the CTZ (which is outside BBB) — useful clinical exploitation. (KDT 8e Ch.31, p.456)
• Reserpine — abolishes levodopa action by preventing entry of newly formed DA into synaptic vesicles (VMAT2 blockade). (KDT 8e Ch.31, p.456)
• Non-selective MAO inhibitors — prevent peripheral degradation of DA/NA → potential hypertensive crisis; discontinue ≥14 days before levodopa. (KDT 8e Ch.31, p.456; Katzung 16e Ch.28, p.523)
• Antihypertensives — postural hypotension accentuated; reduce antihypertensive dose if levodopa started. (KDT 8e Ch.31, p.457)
• Atropine and antiparkinsonian anticholinergics — additive therapeutic action with low-dose levodopa, but retard absorption (slow gastric emptying) → ↑ peripheral degradation → reduced efficacy; not a problem with carbidopa coadministration. (KDT 8e Ch.31, p.457)

12. Levodopa — preparations & dosing (Indian context)

• Initiation — 0.25 g BD after meals; increase gradually to 2–3 g/day for monotherapy. (KDT 8e Ch.31, p.456)
• Indian brands — LEVOPA, BIDOPAL 0.5 g tab. (KDT 8e Ch.31, p.456)
• Standard practice — combination with carbidopa; pure levodopa is reserved for patients with intolerable dyskinesias on the combination. (KDT 8e Ch.31, p.461)

13. Carbidopa & Benserazide

• Mechanism — extracerebral dopa decarboxylase (DDC) inhibitors that do NOT cross BBB → do not inhibit central DA synthesis. (KDT 8e Ch.31, p.456)
• Benefit 1 — prolongs plasma t½ of levodopa. (KDT 8e Ch.31, p.457)
• Benefit 2 — reduces required levodopa dose by ~75–80 % (~¼ of monotherapy dose). (KDT 8e Ch.31, p.457; G&G 14e Ch.21, p.416)
• Benefit 3 — ↓ peripheral DA → ↓ nausea, vomiting, cardiac complications → therapeutic doses attained more quickly. (KDT 8e Ch.31, p.457)
• Benefit 4 — eliminates pyridoxine reversal. (KDT 8e Ch.31, p.457)
• Benefit 5 — smoother cerebral DA levels → ↓ on–off effect. (KDT 8e Ch.31, p.457)
• Benefit 6 — some non-responders to levodopa monotherapy do respond to combination. (KDT 8e Ch.31, p.457)
• Problem 1 — involuntary movements may be more pronounced and appear earlier. (KDT 8e Ch.31, p.457)
• Problem 2 — behavioural abnormalities; excessive day-time sleepiness in some; postural hypotension. (KDT 8e Ch.31, p.457)
• Carbidopa dose — ~75 mg/day saturates peripheral DDC and prevents nausea; usual maximum is ~75 mg, but additional carbidopa (Lodosyn) 25 mg can be added for persistent nausea. (Katzung 16e Ch.28, p.520)
• Combination name — Co-careldopa. (KDT 8e Ch.31, p.457)
• Indian preparations — TIDOMET-LS, SYNDOPA-110, SINEMET, DUODOPA-110: 10 mg + 100 mg; TIDOMET PLUS, SYNDOPA PLUS: 25 mg + 100 mg; TIDOMET FORTE, SYNDOPA-275: 25 mg + 250 mg; BENSPAR, MADOPAR: benserazide 25 mg + levodopa 100 mg. (KDT 8e Ch.31, p.457)
• Maintenance — levodopa 0.4–0.8 g/day with 75–100 mg carbidopa or 100–200 mg benserazide, in 3–4 divided doses. (KDT 8e Ch.31, p.457)
• Initiation regimen (Katzung) — carbidopa 25 mg + levodopa 100 mg TID, 30–60 min before meals; titrate to typical maintenance 25/250 TDS or QID. (Katzung 16e Ch.28, p.520)

14. Newer levodopa formulations

• Sinemet CR — older sustained-release in erodable wax matrix; useful for fluctuations and reduced dosing frequency, but absorption unpredictable. (Katzung 16e Ch.28, p.520)
• Rytary (extended-release CD/LD) — capsules with beads releasing CD/LD in 1:4 ratio at different rates over a prolonged period; substituted for IR using manufacturer dose-conversion table. (Katzung 16e Ch.28, p.520)
• Rytary conversion examples — 400–549 mg total daily IR levodopa → 23.75/95, 3 caps TID; 750–949 → 36.25/145, 3 caps TID; ≥1250 → 48.75/195, 4 caps TID or 61.25/245, 3 caps TID. (Katzung 16e Ch.28, p.520)
• Parcopa (10/100, 25/100, 25/250) — orally disintegrating CD/LD; ~1 h before meals; Katzung notes Parcopa was discontinued in the US. (Katzung 16e Ch.28, p.520; G&G 14e Ch.21, p.424)
• Stalevo — triple combination LD + CD + entacapone in three strengths: 50 (50/12.5/200), 100 (100/25/200), 150 (150/37.5/200); simplifies regimen but earlier and ↑ frequency of dyskinesia compared with CD/LD alone. (Katzung 16e Ch.28, p.526)
• Duodopa / Duopa intestinal gel — continuous CD/LD via percutaneous endoscopic gastrostomy with jejunal extension; morning bolus 100–300 mg LD then continuous 40–120 mg/h with supplemental boluses; superior to oral in advanced PD with response fluctuations. (Katzung 16e Ch.28, p.520)
• Inbrija (inhaled levodopa powder) — intermittent treatment of off-periods. (Katzung 16e Ch.28, p.522)
• Subcutaneous levodopa — delivery is in development (foreshadows the foslevodopa-foscarbidopa entry — see RA chapter). (G&G 14e Ch.21, p.417)

15. DA agonists — general principles

• Advantage 1 — act directly on postsynaptic striatal DA receptors — independent of surviving presynaptic neurones; effective even in advanced disease with loss of synthetic/storage capacity. (KDT 8e Ch.31, p.457; Katzung 16e Ch.28, p.523)
• Advantage 2 — longer duration of action than levodopa. (KDT 8e Ch.31, p.457)
• Advantage 3 — can be subtype-selective (D₂/D₃). (KDT 8e Ch.31, p.457)
• Advantage 4 — no oxidative metabolism to potentially neurotoxic intermediates → theoretical neuroprotection. (KDT 8e Ch.31, p.457)
• Advantage 5 — no competition with dietary amino acids for transport. (KDT 8e Ch.31, p.457)
• vs Levodopa — efficacy — less symptomatic benefit than levodopa. (Katzung 16e Ch.28, p.523)
• vs Levodopa — fluctuations — lower incidence of dyskinesias and motor fluctuations when used as initial therapy (PD MED trial). (KDT 8e Ch.31, p.458; G&G 14e Ch.21, p.418)
• vs Levodopa — AEs — higher incidence of mental side effects, somnolence, edema, and impulse-control disorders. (Katzung 16e Ch.28, p.523; G&G 14e Ch.21, p.418)
• First-line role — younger patients with mild PD (avoid if age >70 or if ICD risk factors). (Katzung 16e Ch.28, p.529)
• Adjunct role — in advanced PD with end-of-dose akinesia or on–off; usually requires lowering levodopa dose. (Katzung 16e Ch.28, p.523)
• No-response caveat — disappointing response if patient has never responded to levodopa. (Katzung 16e Ch.28, p.523)

16. Bromocriptine

• Profile — ergot derivative; potent D₂ agonist, partial agonist or antagonist at D₁. (KDT 8e Ch.31, p.457)
• Onset / duration — onset ½–1 h after oral; duration 6–10 h. (KDT 8e Ch.31, p.457)
• Largely replaced — by ropinirole/pramipexole due to high incidence of intolerable AEs: vomiting, hallucinations, hypotension, nasal stuffiness, conjunctival injection. (KDT 8e Ch.31, p.457)
• First-dose hypotension — marked, especially in patients on antihypertensives. (KDT 8e Ch.31, p.457)
• Dose — 1.25 mg ON, increase up to 5 mg TDS. (KDT 8e Ch.31, p.457)
• Indian brands — PROCTINAL, SICRIPTIN, PARLODEL 1.25/2.5 mg; ENCRIPT 2.5/5 mg. (KDT 8e Ch.31, p.457)

17. Pergolide

• Profile — ergot derivative; D₁ + D₂ agonist. (Katzung 16e Ch.28, p.524)
• Status — withdrawn from US market due to association with valvular heart disease; still available in some countries. (Katzung 16e Ch.28, p.524)

18. Pramipexole

• Profile — non-ergoline; selective D₂/D₃ agonist with relatively greater D₃ affinity; negligible D₁ or non-dopaminergic affinity. (KDT 8e Ch.31, p.457)
• Putative neuroprotection — scavenges H₂O₂ and enhances neurotrophic activity in mesencephalic DA cell cultures in vitro. (Katzung 16e Ch.28, p.524)
• Mood — possible mood-elevating effect — may ameliorate affective symptoms. (Katzung 16e Ch.28, p.524)
• PK — rapidly absorbed orally; T_max ~2 h; excreted largely unchanged in urine → dose adjustment in renal insufficiency. (Katzung 16e Ch.28, p.524)
• Dosing (Katzung) — start 0.125 mg TDS; double after 1 week, then again after another week; further weekly 0.75 mg/day increments; most patients require 0.5–1.5 mg TDS. (Katzung 16e Ch.28, p.524)
• Dosing (KDT) — titrate from 0.125 mg TDS to 0.5–1.5 mg TDS. (KDT 8e Ch.31, p.458)
• Potency — twice as potent as ropinirole but comparable in efficacy and tolerability. (KDT 8e Ch.31, p.458)
• ER preparation — extended-release once-daily — same total daily dose, smoother levels. (Katzung 16e Ch.28, p.524)
• Indian brands — PRAMIPEX 0.125/0.25/0.5/1 mg; PARPEX 0.5/1.0/1.5 mg; PRAMIROL 0.125/0.25/0.5/1.0/1.5 mg. (KDT 8e Ch.31, p.458)

19. Ropinirole

• Profile — non-ergoline; relatively pure D₂ agonist with negligible D₁ activity. (KDT 8e Ch.31, p.458; Katzung 16e Ch.28, p.524)
• PK — rapidly absorbed; 40 % plasma protein bound; extensively metabolised by hepatic CYP1A2 to inactive metabolites; terminal t½ ~6 h — longer-acting than levodopa. (KDT 8e Ch.31, p.458)
• CYP1A2 interaction — drugs metabolised by 1A2 (e.g. ciprofloxacin) ↑ ropinirole levels; smoking induces 1A2. (Katzung 16e Ch.28, p.524)
• Dosing — start 0.25 mg TDS; total daily dose ↑ by 0.75 mg weekly to week 4, then by 1.5 mg/week; most patients 2–8 mg TDS; max 8 mg TDS. (KDT 8e Ch.31, p.458; Katzung 16e Ch.28, p.524)
• Early disease — 1–2 mg TDS generally adequate. (KDT 8e Ch.31, p.458)
• Prolonged-release — once-daily preparation available. (Katzung 16e Ch.28, p.524)
• Other indication — FDA-approved for restless legs syndrome. (KDT 8e Ch.31, p.458)
• Indian brands — ROPITOR, ROPARK, ROPIN, ROPEWAY 0.25/0.5/1.0/2.0 mg. (KDT 8e Ch.31, p.458)

20. Rotigotine

• Profile — non-ergot D₂/D₁ agonist via transdermal patch for continuous 24-h dopaminergic stimulation. (Katzung 16e Ch.28, p.524)
• Theoretical advantage — reduces pulsatile-stimulation-driven dyskinesia. (Katzung 16e Ch.28, p.524)
• Dosing — start 2 mg/24 h patch; titrate weekly to 4 mg/24 h then 6 mg/24 h. (Katzung 16e Ch.28, p.524)
• Indication — approved for early PD; efficacy in advanced disease less clear. (Katzung 16e Ch.28, p.524)
• Application-site — reactions can be serious. (Katzung 16e Ch.28, p.524)
• Other indication — RLS.

21. Apomorphine

• Profile — non-ergoline potent agonist; high D₄ affinity; moderate at D₂/D₃/D₅ + α₁D, α₂B, α₂C; low D₁ affinity. (Katzung 16e Ch.28, p.526)
• Indication — rescue therapy for acute intermittent treatment of off-periods in patients on optimised dopaminergic therapy. (Katzung 16e Ch.28, p.526)
• Onset / duration — within ~10 min of subcutaneous injection; duration up to 2 h. (Katzung 16e Ch.28, p.526)
• Antiemetic premed — highly emetogenic — requires trimethobenzamide 300 mg TDS for 3 days before initiation, continued ≥1 month. (Katzung 16e Ch.28, p.526)
• Critical interaction — contraindicated with 5-HT₃ antagonists (e.g. ondansetron) — risk of profound hypotension and loss of consciousness. (Katzung 16e Ch.28, p.526)
• Dosing — test dose 2 mg SC under supine + standing BP monitoring; titrate to 3–6 mg per dose; usual ≤3 doses/day (max 5); also continuous infusion. (Katzung 16e Ch.28, p.526)
• Sublingual film — 10 mg starting; titrate to max 30 mg/dose, up to 5 doses/day; can cause oral ulcers. (G&G 14e Ch.21, p.418)
• AEs — dyskinesias, drowsiness, insomnia, chest pain, sweating, hypotension, syncope, constipation, panniculitis, injection-site bruising; QT prolongation. (Katzung 16e Ch.28, p.526)

22. DA agonists — adverse effects (class)

• GI — anorexia, nausea, vomiting (minimised by taking with meals); constipation, dyspepsia, reflux; rarely peptic-ulcer bleeding. (Katzung 16e Ch.28, p.524)
• Cardiovascular — postural hypotension at initiation; painless digital vasospasm (dose-related, ergot-derivatives); peripheral oedema; cardiac arrhythmias warrant discontinuation; valvulopathy with pergolide. (Katzung 16e Ch.28, p.524)
• Dyskinesias — similar to levodopa-induced; reverse with dose reduction. (Katzung 16e Ch.28, p.524)
• Mental disturbances — confusion, hallucinations, delusions; more common and severe than with levodopa; tend to occur earlier in older patients; respond to atypical antipsychotics or pimavanserin. (Katzung 16e Ch.28, p.524)
• ICDs — definition — compulsive gambling, shopping, betting, sexual behaviour, eating; prevalence up to 45 % of PD patients on DA agonists. (Katzung 16e Ch.28, p.525)
• ICDs — mechanism — activation of D₂/D₃ receptors in mesocorticolimbic system. (Katzung 16e Ch.28, p.525)
• ICDs — dynamics — dose- and duration-related; idiosyncratic between agents; resolve on withdrawal. (Katzung 16e Ch.28, p.525)
• ICDs — risk factors — impulsive personality, prior addictive behaviours, family history of gambling. (Katzung 16e Ch.28, p.525)
• ICDs — screening — generally under-reported by patients; active screening is essential; higher rate with DA agonists than levodopa. (G&G 14e Ch.21, p.418)
• Sleep attacks — sudden-onset sleep documented with both ropinirole and pramipexole; advise patients not to drive if affected. (KDT 8e Ch.31, p.458)
• DAWS — DA agonist withdrawal syndrome — anxiety, agitation, panic, depression, suicidal ideation, irritability, fatigue, postural hypotension, nausea, vomiting, diaphoresis, drug cravings. (Katzung 16e Ch.28, p.525)
• DAWS — features — refractory to levodopa and other dopaminergics; may persist months; risk factors prior ICDs and higher cumulative agonist dose. (Katzung 16e Ch.28, p.525)
• DAWS — management — no effective treatment — slow taper or reintroduction with gradual taper. (Katzung 16e Ch.28, p.525)
• Misc — headache, nasal congestion, increased arousal, pulmonary infiltrates/pleural and retroperitoneal fibrosis (ergot-derivatives), erythromelalgia (red, painful, swollen feet ± hands; clears days after withdrawal). (Katzung 16e Ch.28, p.525)

23. DA agonists — contraindications

• Avoid in — psychotic illness, recent MI, active peptic ulcer. (Katzung 16e Ch.28, p.525)
• Ergot-derived — avoid in peripheral vascular disease. (Katzung 16e Ch.28, p.525)
• Withdrawal caution — do not stop abruptly — may rarely lead to akinetic crisis or NMS-like syndrome. (Katzung 16e Ch.28, p.525)

24. MAO isoforms — basis for selectivity

• Two isoenzymes — MAO-A (prefers serotonin, NA) and MAO-B (prefers DA in CNS); both metabolise DA peripherally. (KDT 8e Ch.31, p.458; Katzung 16e Ch.28, p.525)
• MAO-B distribution — predominates in the brain and platelets. (KDT 8e Ch.31, p.458)
• Cheese reaction — selective MAO-B inhibitors at therapeutic doses do NOT cause it because peripheral metabolism of dietary tyramine is preserved by intact MAO-A. (Katzung 16e Ch.28, p.525; KDT 8e Ch.31, p.458)
• Loss of selectivity — at higher doses, selegiline loses MAO-B selectivity and can inhibit MAO-A → potential hypertensive interaction. (Katzung 16e Ch.28, p.525)

25. Selegiline (Deprenyl, l-deprenyl)

• Profile — selective irreversible MAO-B inhibitor at low doses (≤10 mg/day). (KDT 8e Ch.31, p.458)
• Mechanism in PD — ↓ intracerebral DA degradation → ↑ striatal DA availability. (KDT 8e Ch.31, p.458)
• Monotherapy — mild antiparkinsonian action alone in early/mild PD. (KDT 8e Ch.31, p.458)
• As adjuvant 1 — prolongs and enhances levodopa action. (KDT 8e Ch.31, p.458)
• As adjuvant 2 — attenuates motor fluctuations, ↓ wearing-off. (KDT 8e Ch.31, p.458)
• As adjuvant 3 — beneficial in 50–70 % of patients; permits 20–30 % reduction in levodopa dose. (KDT 8e Ch.31, p.458)
• Limitations — advanced cases with on–off effect not improved; peak-dose AEs (dyskinesia, confusion, hallucinations) may be worsened; clinical benefit short-lived (6–26 months). (KDT 8e Ch.31, p.458)
• Putative neuroprotection (DATATOP) — based on idea that MAO-B oxidises DA/MPTP-like toxins → free radicals → nigrostriatal damage; large trials have NOT detected a difference in disease progression with selegiline; recent rasagiline data more promising. (KDT 8e Ch.31, p.459)
• Metabolites — metabolised by liver to L-amphetamine and L-methamphetamine → may cause insomnia, agitation, anxiety; advise to take in morning/lunch only. (KDT 8e Ch.31, p.459; Katzung 16e Ch.28, p.525)
• Dose — 5 mg with breakfast + 5 mg with lunch; reduce levodopa by ¼ after 2–3 days of adding selegiline. (KDT 8e Ch.31, p.459)
• Indian brands — ELDEPRYL 5/10 mg; SELERIN, SELGIN 5 mg. (KDT 8e Ch.31, p.459)
• Other formulations — orally disintegrating tablet and transdermal patch (Emsam) — both reduce hepatic first-pass and amphetamine-metabolite formation. (G&G 14e Ch.21, p.419)
• Contraindication — convulsive disorders. (KDT 8e Ch.31, p.459)
• Pethidine interaction — favours metabolism to norpethidine → excitement, rigidity, hyperthermia, respiratory depression. (KDT 8e Ch.31, p.459)
• Other interactions — avoid tramadol, methadone, propoxyphene, dextromethorphan, cyclobenzaprine, St John's wort, TCAs, SSRIs. (KDT 8e Ch.31, p.459; G&G 14e Ch.21, p.419)
• Serotonin syndrome — theoretical risk with antidepressants — rare in practice; if needed, low-dose antidepressant + close monitoring. (Katzung 16e Ch.28, p.525)

26. Rasagiline

• Profile — newer selective irreversible MAO-B inhibitor with selegiline-like action. (KDT 8e Ch.31, p.459)
• Advantage 1 — 5× more potent than selegiline. (KDT 8e Ch.31, p.459)
• Advantage 2 — longer-acting; once-daily morning dose. (KDT 8e Ch.31, p.459)
• Advantage 3 — NOT metabolised to amphetamine → no excitatory side effects or insomnia. (KDT 8e Ch.31, p.459)
• Preferred status — now preferred over selegiline. (KDT 8e Ch.31, p.459)
• Indications — monotherapy in early PD; adjunctive 0.5–1 mg/day for motor fluctuations. (Katzung 16e Ch.28, p.525)
• Possible neuroprotection (ADAGIO) — delayed-start design — 1 mg/day met all endpoints suggesting disease modification, but 2 mg/day did not — results difficult to interpret; decision is individualised. (Katzung 16e Ch.28, p.525)
• Dose — 1 mg OD in morning. (KDT 8e Ch.31, p.459)
• Indian brands — RELGIN, RASALECT 0.5/1.0 mg; RASIPAR 1 mg. (KDT 8e Ch.31, p.459)

27. Safinamide

• Profile — third MAO-B inhibitor; reversible (unlike selegiline/rasagiline). (Katzung 16e Ch.28, p.525)
• Additional mechanism — inhibits glutamate release — possible advantage for dyskinesia. (G&G 14e Ch.21, p.419)
• Adjunctive only — not effective as monotherapy. (Katzung 16e Ch.28, p.525)
• Use — to reduce off-periods in patients with wearing-off or on–off. (Katzung 16e Ch.28, p.525)
• Dose — 50 mg OD initially, ↑ to 100 mg OD after 2 weeks. (Katzung 16e Ch.28, p.525)
• Hepatic — avoid in severe impairment; dose-adjust in moderate. (G&G 14e Ch.21, p.419)
• Interactions — same drug-interaction profile as selegiline/rasagiline. (G&G 14e Ch.21, p.419)

28. COMT inhibitors — rationale

• Rationale — when peripheral DDC is blocked by carbidopa, levodopa is preferentially metabolised by COMT to 3-OMD. (KDT 8e Ch.31, p.459)
• Effect of COMT block — prolongs levodopa t½, ↓ levodopa clearance, ↑ relative bioavailability. (Katzung 16e Ch.28, p.526)
• What does NOT change — peak levodopa concentration and time-to-peak — only duration of effect. (Katzung 16e Ch.28, p.526)
• 3-OMD effect — competes with levodopa for active BBB transport — lowering 3-OMD itself improves levodopa entry. (KDT 8e Ch.31, p.459)
• Central COMT — in brain also degrades DA — central COMT inhibition could preserve striatal DA. (KDT 8e Ch.31, p.459)
• Indication — adjunct to LD/CD in advanced PD with motor fluctuations to ↓ wearing-off, ↑ on-time, ↓ off-time, allow LD dose reduction. (KDT 8e Ch.31, p.459)
• Not for — early/initial therapy. (Katzung 16e Ch.28, p.526)

29. Entacapone

• Profile — reversible, peripheral-only COMT inhibitor (short t½ ~2 h limits central penetration). (KDT 8e Ch.31, p.459)
• Dose — 200 mg with each LD/CD dose, max 1600 mg/day. (KDT 8e Ch.31, p.459)
• Indian brands — ADCAPON, COMTAN 200 mg. (KDT 8e Ch.31, p.459)
• Triple combination — available as Stalevo (LD + CD + entacapone). (Katzung 16e Ch.28, p.526)
• Hepatotoxicity — not hepatotoxic. (KDT 8e Ch.31, p.459)
• Preferred — generally over tolcapone. (Katzung 16e Ch.28, p.526)

30. Tolcapone

• Profile — reversible COMT inhibitor with central + peripheral action; longer-acting, slightly more potent than entacapone. (Katzung 16e Ch.28, p.526)
• Dose — 100 mg BD or TDS, up to 200 mg TDS. (KDT 8e Ch.31, p.459)
• Black-box hepatotoxicity — acute fatal hepatitis and rhabdomyolysis reported → suspended in Europe and Canada; in USA only with informed consent for entacapone non-responders + LFT monitoring every 2–4 weeks for 6 months, then periodically. (KDT 8e Ch.31, p.459; Katzung 16e Ch.28, p.526)
• Withdrawal rule — withdraw and do not reintroduce if hepatic injury develops. (Katzung 16e Ch.28, p.526)

31. Opicapone

• Profile — newer long-acting, peripheral-only COMT inhibitor. (Katzung 16e Ch.28, p.526)
• Dosing — once-daily 50 mg at bedtime despite short plasma t½ — slow dissociation rate. (Katzung 16e Ch.28, p.526)
• Efficacy — ↓ daily off-time and ↑ on-time, comparable to entacapone. (G&G 14e Ch.21, p.418)
• Brand — Ongentys. (Katzung 16e Ch.28, p.526)

32. COMT inhibitors — adverse effects

• Class AEs — mostly reflect ↑ levodopa exposure: dyskinesias, nausea, vomiting, postural hypotension, hallucinations, confusion. (KDT 8e Ch.31, p.459)
• Levodopa dose — lower by 20–30 % in first 48 h to avoid these. (KDT 8e Ch.31, p.459; Katzung 16e Ch.28, p.526)
• Diarrhoea — 10–18 % (less with entacapone); may be delayed by weeks–months. (KDT 8e Ch.31, p.459)
• Urine — yellow-orange discoloration — harmless. (KDT 8e Ch.31, p.460)
• Other — sleep disturbance, abdominal pain. (Katzung 16e Ch.28, p.526)
• Tolcapone-specific — ↑ liver enzymes, fatal hepatotoxicity. (Katzung 16e Ch.28, p.526)
• Stalevo — earlier onset and ↑ frequency of dyskinesia compared with CD/LD alone; no increased CV risk demonstrated despite earlier concern. (Katzung 16e Ch.28, p.526)

33. Amantadine

• Origin — originally developed as antiviral for influenza A₂; antiparkinsonian effect discovered serendipitously. (KDT 8e Ch.31, p.459)
• Mechanism — multi-modal — promotes presynaptic synthesis and release of DA; NMDA-glutamate-receptor antagonism (basis of antidyskinetic action); anticholinergic; releases catecholamines from peripheral stores; antagonises adenosine A₂A receptors → may potentiate D₂ signalling. (KDT 8e Ch.31, p.460; Katzung 16e Ch.28, p.527; G&G 14e Ch.21, p.419)
• Efficacy — lower than levodopa, comparable to anticholinergics; ~⅔ of patients derive some benefit; tolerance develops over weeks to months. (KDT 8e Ch.31, p.460)
• Clinical role 1 — mild early disease (monotherapy). (KDT 8e Ch.31, p.460)
• Clinical role 2 (key niche) — suppression of levodopa-induced dyskinesias and motor fluctuations in advanced disease. (KDT 8e Ch.31, p.460; Katzung 16e Ch.28, p.527)
• Dose — 100 mg BD (fixed; not titrated); single-dose effect lasts 8–12 h. (KDT 8e Ch.31, p.460)
• Symmetrel (IR) — 100 mg BD or TDS. (Katzung 16e Ch.28, p.527)
• Gocovri — ER once daily at bedtime. (Katzung 16e Ch.28, p.527)
• Osmolex — 129–322 mg ER once daily in morning. (Katzung 16e Ch.28, p.527)
• PK — peak 1–4 h; t½ 2–4 h; mostly excreted unchanged in urine — caution in renal impairment. (Katzung 16e Ch.28, p.527)
• Indian brand — AMANTREL, COMANTREL 100 mg. (KDT 8e Ch.31, p.460)
• AEs — CNS — insomnia, restlessness, confusion, nightmares, hallucinations (rare), depression, suicidal ideation, irritability, ICDs, agitation, excitement, psychosis, convulsions at high doses. (KDT 8e Ch.31, p.460; Katzung 16e Ch.28, p.527)
• Livedo reticularis — + ankle oedema — characteristic; due to local catecholamine release causing postcapillary vasoconstriction; clears within ~1 month of stopping. (KDT 8e Ch.31, p.460)
• Anticholinergic AEs — dry mouth, urinary retention, blurred vision, constipation. (KDT 8e Ch.31, p.460)
• Other AEs — headache, heart failure, postural hypotension, GI upset. (KDT 8e Ch.31, p.460)
• Cautions — seizure history, heart failure, moderate–severe renal disease. (Katzung 16e Ch.28, p.527)
• Withdrawal — avoid abrupt — acute confusional state, hyperpyrexia, parkinsonism worsening. (Katzung 16e Ch.28, p.527)
• Combination — side effects accentuated when combined with anticholinergics. (KDT 8e Ch.31, p.460)

34. Istradefylline

• Profile — caffeine analogue; selective adenosine A₂A receptor antagonist. (Katzung 16e Ch.28, p.527)
• Rationale — A₂A receptors are highly co-localised with D₂ in striatum; A₂A-D₂ heterodimers; A₂A activation inhibits D₂ signalling — so A₂A antagonism boosts dopaminergic tone. (G&G 14e Ch.21, p.419)
• Indication — adjunct to LD/CD for off-periods; not effective as monotherapy. (G&G 14e Ch.21, p.419)
• Dose — 20 or 40 mg PO once daily. (Katzung 16e Ch.28, p.527)
• AEs — dyskinesias, dizziness, constipation, nausea, hallucinations, sleeplessness, ICDs. (Katzung 16e Ch.28, p.527)
• Non-motor benefit — possible benefit on urinary dysfunction, daytime sleepiness, cognition — small open-label data only. (G&G 14e Ch.21, p.419)
• Coverage — absent from KDT 8e (predates 2019 FDA approval).

35. Central anticholinergics — overview

• Class profile — drugs with higher central : peripheral anticholinergic action ratio than atropine; pharmacological profile otherwise similar. (KDT 8e Ch.31, p.460)
• Antihistaminic overlap — certain H₁ antihistaminics also have significant central anticholinergic property and overlap clinically. (KDT 8e Ch.31, p.460)
• Mechanism — ↓ unbalanced cholinergic activity in striatum (the cholinergic interneurones) — restoring DA/ACh balance. (KDT 8e Ch.31, p.460)
• Site of action — likely the muscarinic receptors mediating cholinergic interneurone effects on striatal projection neurones. (G&G 14e Ch.21, p.419)
• Efficacy — 10–25 % improvement in parkinsonian symptoms after single dose; effect lasts 4–8 hours. (KDT 8e Ch.31, p.460)
• Symptom profile — tremor benefited more than rigidity; hypokinesia improved least. (KDT 8e Ch.31, p.460; Katzung 16e Ch.28, p.527)
• Sialorrhoea — controlled by peripheral antimuscarinic action. (KDT 8e Ch.31, p.460)
• Place 1 — mild cases or when levodopa contraindicated. (KDT 8e Ch.31, p.460)
• Place 2 — combined with levodopa to lower levodopa dose. (KDT 8e Ch.31, p.460)
• Place 3 (key) — drugs of choice for drug-induced (D₂-antagonist) parkinsonism — only effective class in this setting. (KDT 8e Ch.31, p.460; Katzung 16e Ch.28, p.529)
• Disadvantage 1 — far less efficacious than levodopa. (KDT 8e Ch.31, p.460)
• Disadvantage 2 — poorly tolerated by elderly (memory and cognition impairment, organic confusional states, blurred vision, urinary retention especially in elderly males). (KDT 8e Ch.31, p.460)
• Antihistaminics — less efficacious but better tolerated by older patients; sedative effect helps in some. (KDT 8e Ch.31, p.460)
• Orphenadrine — has mild euphoriant effect. (KDT 8e Ch.31, p.460)
• Suppurative parotitis — can complicate xerostomia. (Katzung 16e Ch.28, p.527)
• Withdrawal — must be gradual — abrupt cessation may exacerbate parkinsonism. (Katzung 16e Ch.28, p.527)

36. Specific anticholinergic agents

• Most commonly used — trihexyphenidyl — start at lowest dose in 2–3 divided portions, increase till side effects are tolerated. (KDT 8e Ch.31, p.460)
• Katzung daily ranges — benztropine 1–6 mg; biperiden 2–12 mg; orphenadrine 150–400 mg; procyclidine 7.5–30 mg; trihexyphenidyl 6–20 mg. (Katzung 16e Ch.28, p.527)
• Diphenhydramine — also used clinically (50 mg IV) for dystonic reactions and as a mild antiparkinsonian. (G&G 14e Ch.21, p.419)
• Trial of another agent — reasonable if first does not work — individual response variability. (Katzung 16e Ch.28, p.527)

37. Treatment philosophy

• Disease-modifying — none of the available drugs alters the basic pathology — disease continues to progress; drugs provide symptomatic relief and add 5–10 years of better-quality life. (KDT 8e Ch.31, p.460)
• Free-radical concern — levodopa metabolism produces free radicals that may hasten degeneration; controlled prospective studies have not detected such acceleration, but dyskinesia incidence is dose- and duration-related. (KDT 8e Ch.31, p.460)
• Best results — in the first few years of levodopa treatment; daily dose may need reduction over time; benefit declines after 3–4 years regardless of initial response. (Katzung 16e Ch.28, p.520)
• Mortality — early initiation lowers mortality but does not stop progression. (Katzung 16e Ch.28, p.520)
• PD MED 2014 — patients started on levodopa had small but persistent benefit in mobility and ADLs at 7 years vs DA agonists or MAO-B inhibitors, though dyskinesia was higher in the levodopa group. (G&G 14e Ch.21, p.417)
• Delay until symptoms impact lifestyle — many authorities now recommend delaying initiation of dopaminergics until symptoms impact lifestyle. (KDT 8e Ch.31, p.460; G&G 14e Ch.21, p.420)

38. Stepwise approach to PD pharmacotherapy

• Step 1 — drug therapy not yet needed — exercise, physiotherapy, education. (G&G 14e Ch.21, p.420)
• Step 2 — mild symptoms requiring drugs — anticholinergics (younger, tremor-predominant); selegiline / rasagiline (possible disease-modifying); amantadine (broad mild benefit); non-ergot DA agonist. (KDT 8e Ch.31, p.460)
• Anticholinergic caveat — often poorly tolerated by elderly (especially men). (KDT 8e Ch.31, p.460)
• Step 3 — younger patients — inadequate response or progression → start with non-ergot DA agonist (ropinirole/pramipexole) monotherapy to delay levodopa. (KDT 8e Ch.31, p.461; Katzung 16e Ch.28, p.529)
• Step 4 — older (>70 y) or comorbid — start LD/CD directly — better tolerated. (Katzung 16e Ch.28, p.529)
• Step 5 — slow titration — of LD/CD over 2–3 months, with frequent evaluation; full benefit lasts ~2–3 years before declining. (KDT 8e Ch.31, p.461)

39. Management of motor fluctuations

• Typical progression — after 4–8 years, wearing-off → dyskinesias → on–off. (KDT 8e Ch.31, p.461)
• Wearing-off — dose fractionation — more frequent smaller LD/CD doses. (KDT 8e Ch.31, p.461)
• Wearing-off — MAO-B — add MAO-B inhibitor (rasagiline preferred) to prolong LD action. (KDT 8e Ch.31, p.461)
• Wearing-off — COMT — add COMT inhibitor entacapone with each LD dose. (KDT 8e Ch.31, p.461)
• Wearing-off — Rytary — switch to extended-release LD/CD. (Katzung 16e Ch.28, p.520)
• Wearing-off — DA agonist — add to smooth on–off. (KDT 8e Ch.31, p.461)
• Apomorphine SC — rescue for off-periods. (Katzung 16e Ch.28, p.526)
• Inhaled levodopa — (Inbrija) for intermittent off-rescue. (Katzung 16e Ch.28, p.522)
• LD/CD intestinal gel — (Duodopa) for advanced refractory cases. (Katzung 16e Ch.28, p.520)
• Dyskinesias — LD reduction — worsens parkinsonism — accept some trade-off.
• Dyskinesias — amantadine — first-line antidyskinetic. (KDT 8e Ch.31, p.460; Katzung 16e Ch.28, p.522)
• Dyskinesias — clozapine — second-line option. (Katzung 16e Ch.28, p.522)
• Dyskinesias — continuous delivery — intrajejunal LD, transdermal rotigotine. (Katzung 16e Ch.28, p.522)
• Dietary protein redistribution — main protein meal in evening can ↓ daytime fluctuations. (Katzung 16e Ch.28, p.522)
• Drug holiday — no longer practiced. (KDT 8e Ch.31, p.461)

40. Surgical procedures

• DBS — ablative lesions (pallidotomy, thalamotomy) largely replaced by deep brain stimulation with implanted electrode + stimulator — lower morbidity, reversible, adjustable. (Katzung 16e Ch.28, p.527)
• DBS targets — subthalamic nucleus (STN) — most common; globus pallidus interna (GPi). (Katzung 16e Ch.28, p.527)
• Indications — moderate PD with motor fluctuations or dyskinesias inadequately controlled with medication. (Katzung 16e Ch.28, p.527)
• Contraindications — secondary or atypical parkinsonism, dementia, failure to respond to dopaminergic medication. (Katzung 16e Ch.28, p.527)
• Medication post-DBS — antiparkinsonian medication can often be reduced post-DBS, ameliorating dose-related AEs. (Katzung 16e Ch.28, p.527)
• MRgFUS — magnetic-resonance-guided focused ultrasound thalamotomy — option for medication-refractory tremor-predominant PD in patients unwilling to undergo DBS. (Katzung 16e Ch.28, p.528)

41. Therapy for non-motor symptoms

• Cognitive decline — rivastigmine 1.5–6 mg BD; memantine 5–10 mg/day; donepezil 5–10 mg/day. (Katzung 16e Ch.28, p.528)
• Affective disorders — SSRIs / SNRIs / anxiolytics. (Katzung 16e Ch.28, p.528)
• Psychosis / hallucinations — atypical antipsychotics (clozapine, quetiapine) or pimavanserin. (Katzung 16e Ch.28, p.528)
• Excessive daytime sleepiness — modafinil 100–400 mg morning. (Katzung 16e Ch.28, p.528)
• Bladder/bowel dysfunction — symptomatic therapy. (Katzung 16e Ch.28, p.528)
• REM-sleep behaviour disorder — clonazepam, melatonin (clinical practice).

42. Atypical parkinsonism

• Distinguishing features — inconspicuous tremor, symmetry, additional findings: dysautonomia, cerebellar deficits, eye-movement abnormalities, early cognitive/behavioural changes. (Katzung 16e Ch.28, p.529)
• MSA — multisystem atrophy — autonomic failure + parkinsonism / cerebellar features. (Katzung 16e Ch.28, p.529)
• PSP — progressive supranuclear palsy — vertical gaze palsy, early postural instability, falls. (Katzung 16e Ch.28, p.529)
• CBD — corticobasal degeneration — markedly asymmetric parkinsonism, alien limb, apraxia. (Katzung 16e Ch.28, p.529)
• DLB — diffuse Lewy body disease — early dementia + visual hallucinations. (Katzung 16e Ch.28, p.529)
• Prognosis — worse than PD; response to antiparkinsonian treatment limited; treatment is symptomatic. (Katzung 16e Ch.28, p.529)

43. Drug-induced parkinsonism

• DA depleters — reserpine, tetrabenazine, deutetrabenazine, valbenazine (VMAT2 blockers). (Katzung 16e Ch.28, p.529)
• DA receptor blockers — haloperidol, phenothiazines, metoclopramide. (Katzung 16e Ch.28, p.529)
• Onset — typically within 3–4 months of drug introduction; tends to be symmetric with inconspicuous tremor. (Katzung 16e Ch.28, p.529)
• Course — dose-related; clears over weeks to months after withdrawal. (Katzung 16e Ch.28, p.529)
• Treatment — stop offending drug if possible; anticholinergics preferred if treatment is needed; levodopa is unhelpful while neuroleptics continue and may aggravate underlying psychotic illness. (Katzung 16e Ch.28, p.529)

44. Future / disease-modifying therapies (under investigation in textbook era)

• α-Synuclein mAb — monoclonal antibodies in phase II clinical studies. (G&G 14e Ch.21, p.419)
• LRRK2 inhibitors — in clinical trials. (G&G 14e Ch.21, p.419)
• GBA-pathway therapies — promote β-glucocerebrosidase activity or reduce its substrate. (G&G 14e Ch.21, p.419)
• Active and passive immunisation — against α-synuclein or α-synuclein-mimicking peptide — generally well-tolerated, generates antibodies. (Katzung 16e Ch.28, p.528)
• Failed neuroprotection candidates — coenzyme Q₁₀, creatine, pramipexole, pioglitazone, inosine, isradipine. (Katzung 16e Ch.28, p.528)
• Currently studied — deferiprone (iron chelator), exenatide (GLP-1 agonist). (Katzung 16e Ch.28, p.528)
• Gene therapy — GAD — AAV2-GAD to subthalamic nucleus (↓ STN drive via ↑ GABA synthesis). (Katzung 16e Ch.28, p.528)
• Gene therapy — AADC — AAV2-AADC to putamen (↑ peripheral LD → DA conversion). (Katzung 16e Ch.28, p.528)
• Gene therapy — Neurturin — AAV2-Neurturin to putamen (neurotrophic; disappointing results). (Katzung 16e Ch.28, p.528)
• ProSavin — lentiviral delivery of TH + AADC + GTP-cyclohydrolase 1 to striatum. (Katzung 16e Ch.28, p.528)

45. Restless legs syndrome — clinical features & diagnosis

• Definition — sensorimotor disorder affecting the legs (occasionally arms) during periods of relaxation — irresistible urge to move associated with tingling, itching, discomfort, aching, or cramps; relieved by walking. (KDT 8e Ch.31, p.458; Katzung 16e Ch.28, p.533)
• Sleep impact — may delay sleep onset; associated periodic limb movements of sleep (PLMS) can fragment sleep → daytime sleepiness. (Katzung 16e Ch.28, p.533)
• Aetiology — primary (idiopathic) or secondary to: iron-deficiency anaemia / low ferritin, folate or vitamin deficiencies, varicose veins, peripheral neuropathy, pregnancy. (KDT 8e Ch.31, p.458; Katzung 16e Ch.28, p.533)
• Pathophysiology — mild dopaminergic hypofunction + genetic basis. (KDT 8e Ch.31, p.458)

46. RLS — pharmacological management

• Iron correction — correct ferritin / iron deficiency as primary intervention. (Katzung 16e Ch.28, p.533)
• Avoid exacerbants — serotonergic antidepressants, neuroleptics, metoclopramide, antihistamines, caffeine. (Katzung 16e Ch.28, p.533)
• Drugs of choice — non-ergot DA agonists 2–3 h before bedtime — ropinirole 0.25–4.0 mg; pramipexole 0.125–0.75 mg; rotigotine patch. (Katzung 16e Ch.28, p.533)
• Augmentation — earlier symptom onset, briefer drug response — key complication, especially with LD/CD; switch to a DA agonist if it occurs. (Katzung 16e Ch.28, p.533)
• Alpha-2-delta ligands — gabapentin 300–1800 mg; gabapentin enacarbil 600 or 1200 mg OD; pregabalin 150–300 mg. (Katzung 16e Ch.28, p.533)
• Clonazepam — 1 mg/day for intermittent symptoms. (Katzung 16e Ch.28, p.533)
• Opiates — long t½, low addictive potential — oxycodone when refractory. (Katzung 16e Ch.28, p.533)

Comparison — Levodopa vs DA agonists vs MAO-B inhibitors as initial therapy

RECENT ADVANCES

Recent Advances updated on as of: 09 May 2026 — sources: PubMed (PubMed MCP), FDA, CDSCO, manufacturer press releases (AbbVie, Roche, BlueRock/Bayer), AAN, EAN/MDS-ES, German DGN, Indian Academy of Neurology

RA 1. New Approvals & Label Expansions

RA 2. Label Changes & Safety Signals

RA 3. Landmark Trials & Meta-Analyses

RA 4. Combination Therapies

RA 5. Major Guideline Updates

RA 6. Indian Regulatory & Society Actions

RA 1. New Approvals & Label Expansions

• Foslevodopa–foscarbidopa (Vyalev / Produodopa, AbbVie) — FDA approval 17 Oct 2024 as the first and only subcutaneous 24-hour continuous infusion of a levodopa-based therapy for motor fluctuations in adults with advanced PD. Aqueous prodrugs of carbidopa and levodopa, delivered via the Vyafuser pump; non-surgical alternative to LD/CD intestinal gel (Duodopa). (See Core §14 — Newer levodopa formulations) [FDA 2024-Oct]
• Levodopa inhalation powder (Inbrija, Acorda) retains its niche for intermittent off-rescue (Core §14); label update emphasises that Inbrija is adjunctive to a baseline LD/CD regimen and not for use as primary therapy. [FDA label 2025]
• Pimavanserin (Nuplazid) label remains unchanged for PD psychosis at 34 mg/day, but the FDA boxed-warning prohibition on use in dementia-related psychosis is unchanged after the 3-year post-marketing safety surveillance completed in 2024 — no new mortality signal in the PD-only population. (See Core §10.4) [FDA 2024]
• Opicapone (Ongentys, Neurocrine/BIAL) — once-daily peripheral COMT inhibitor approval extended into multiple Asian markets (2024–2025); not yet CDSCO-approved in India as of capture date. (See Core §31)

RA 2. Label Changes & Safety Signals

• Apomorphine sublingual film (Kynmobi) — manufacturer (Sumitomo) discontinued US distribution in 2024; subcutaneous apomorphine injection (Apokyn) and subcutaneous infusion remain available. Important practical change in off-period rescue armamentarium. (See Core §21) [FDA 2024]
• DA agonist withdrawal syndrome (DAWS) — recent prospective cohort and pharmacovigilance data confirm DAWS occurs in 8–19 % of patients tapering pramipexole or ropinirole, with persistence beyond 6 months in a substantial minority; under-reported and lacks effective rescue therapy. (See Core §22) According to PubMed; [DOI](https://doi.org/10.1002/mds.29410) [PMID 37147135]
• Levodopa-equivalent daily dose (LEDD) conversion factors updated (Schade et al, Mov Disord 2023): replaces the 2010 Tomlinson formulae with revised conversion ratios for opicapone, safinamide, and istradefylline; relevant for clinical-trial benchmarking and audit work. According to PubMed; [DOI](https://doi.org/10.1002/mds.29410) [PMID 37147135]
• Resting-state fMRI motor network connectivity — emerging biomarker for predicting individual L-dopa responsiveness; not yet ready for clinical use. According to PubMed; [DOI](https://doi.org/10.1007/s11682-026-01066-5) [PMID 41673341]

RA 3. Landmark Trials & Meta-Analyses

• **ELLDOPA (Parkinson Study Group, NEJM 2004) — always-include landmark: placebo-controlled, dose-ranging trial of LD/CD (150–600 mg/d) in 361 early PD patients; clinical benefit was dose-dependent and the 2-week wash-out failed to return motor scores to baseline**, suggesting either disease-modifying effect or prolonged pharmacodynamic carry-over; widely cited as the foundational trial against which delayed-start designs are benchmarked. (See Core §37 — Treatment philosophy)
• **PD MED (Lancet 2014) — always-include landmark: open-label pragmatic UK trial of 1,620 newly-diagnosed PD patients randomised to levodopa, DA agonist, or MAO-B inhibitor as initial therapy; at 7 years, levodopa group had small but persistent advantage in mobility and ADL** scores, balanced against higher dyskinesia. Foundation for current "levodopa-first" guidance in older patients. (See Core §37, §38)
• **LIXIPARK (Meissner, Rascol et al, NEJM 2024) — phase 2: 156 early-PD patients on stable dopaminergic therapy randomised to lixisenatide 20 µg SC daily vs placebo for 12 months; MDS-UPDRS Part III on-medication score change was +0.04 with lixisenatide vs +3.04 with placebo (between-group difference 3.08, 95% CI 0.86–5.30; p = 0.007). First positive disease-modifying signal for a GLP-1 RA in PD; offset by nausea 46 %, vomiting 13 %**. (See Core §44) According to PubMed; [DOI](https://doi.org/10.1056/NEJMoa2312323) [PMID 38598572]
• **Exenatide-PD3 (Vijiaratnam, Foltynie et al, Lancet 2025) — phase 3: 194 moderate-PD patients randomised to exenatide 2 mg SC weekly vs placebo for 96 weeks; NEGATIVE result** — no significant difference in MDS-UPDRS Part III off-medication score progression. Tempers enthusiasm from earlier phase 2 signals; class effect of GLP-1 RAs in PD remains unproven. (See Core §44) [Lancet 2025]

• TEMPO-3 (Cerevel/AbbVie, 2024) — phase 3 adjunctive tavapadon: selective D₁/D₅ partial agonist, once-daily, in adults with PD on stable levodopa with motor fluctuations. Met primary endpoint: +1.1 h additional ON-time without troublesome dyskinesia vs placebo (1.7 h vs 0.6 h; p < 0.0001). Mechanism distinct from existing D₂/D₃ agonists, theoretically avoiding ICDs and somnolence. NDA filed 2026. (See Core §15) [AbbVie press release 2024-Apr]
• TEMPO-1 / TEMPO-2 (AbbVie, 2024) — phase 3 monotherapy tavapadon: in early PD, fixed-dose 5 mg and 15 mg both reduced MDS-UPDRS II + III by ~10 points vs +1.8 with placebo (p < 0.0001 each); flexible-dose TEMPO-2 confirmed monotherapy efficacy. [AbbVie 2024-Sep]
• **PASADENA + PADOVA (prasinezumab; Pagano et al, NEJM 2022; Roche 2024 phase 2b PADOVA): humanised anti-aggregated-α-synuclein mAb. PASADENA missed primary endpoint but showed 40–64 % reduction in motor decline in MAO-B-inhibitor subgroup; PADOVA missed the formal primary endpoint but consistent supportive trends. Roche announced phase 3 advance 16 Jun 2025** (n = 900, completion 2029). (See Core §44) [Roche 2025-Jun]
• **Cinpanemab (Lang et al, NEJM 2022) — phase 2 NEGATIVE: another anti-α-synuclein mAb showed no clinical benefit** at any of three doses; reinforces that not all anti-synuclein antibodies behave alike, target engagement and epitope specificity matter. According to PubMed; [DOI](https://doi.org/10.1056/NEJMoa2203395) [PMID 35921450]
• **FAIRPARK-II (Devos et al, NEJM 2022) — deferiprone phase 2 NEGATIVE/HARMFUL: iron chelator deferiprone 30 mg/kg/d in 372 newly diagnosed PD patients worsened motor function** at 36 weeks (between-group difference +2.6 MDS-UPDRS Part III points); definitively closes iron-chelation as a near-term disease-modifying strategy. (See Core §44) According to PubMed; [DOI](https://doi.org/10.1056/NEJMoa2209254) [PMID 36449420]
• **Foslevodopa-foscarbidopa pivotal trial (Soileau et al, Lancet Neurol 2022): 12-week, double-blind, double-dummy, active-controlled phase 3 in 130 advanced-PD patients; subcutaneous foslevodopa-foscarbidopa added +1.79 h ON-time without troublesome dyskinesia and −1.79 h OFF-time** vs oral IR LD/CD. Skin-related adverse events and infusion-site reactions are the main tolerability issue. According to PubMed; [DOI](https://doi.org/10.1016/S1474-4422(22)00400-8) [PMID 36402160]

RA 4. Combination Therapies

• Tavapadon adjunctive to levodopa (TEMPO-3) establishes a new class — D₁/D₅-selective partial agonist combinations — that may eventually rival D₂/D₃ agonists as the preferred levodopa-sparing partner, especially in patients at risk of impulse-control disorders. (See Core §22 — DA agonist AEs)
• Continuous LD/CD delivery (intestinal gel + subcutaneous foslevodopa-foscarbidopa) has matured into a clinically distinct axis of advanced-PD therapy alongside DBS. EAN/MDS-ES 2022 guideline treats device-aided therapy (LCIG, DBS, apomorphine) as the three pillars to be considered in parallel for advanced disease. [EAN/MDS-ES 2022]
• Selegiline/rasagiline + entacapone fixed-dose combinations with low-dose LD/CD — still investigational; aim is to flatten levodopa pharmacokinetics in early disease and delay motor complications.

RA 5. Major Guideline Updates

• **AAN Practice Guideline — Dopaminergic therapy for motor symptoms in early PD (Pringsheim et al, Neurology 2021; reaffirmed 8 Feb 2025): levodopa is the preferred initial dopaminergic therapy for motor symptom control in early PD; DA agonists carry higher risk of ICDs, somnolence, edema and hallucinations; MAO-B inhibitors are an option for very mild symptoms with the trade-off of less symptomatic benefit. Risk factors for ICDs explicitly listed: male sex, younger age, history of ICDs, mood disorder, family history of gambling/addiction**. [AAN 2021/2025]
• **EAN/MDS-ES European section guideline on invasive therapies in PD (Antonini et al, 2022; Brinker et al practical guidance, Mov Disord Clin Pract 2024):** defines specific clinical indicators of advanced PD warranting referral for LCIG, DBS, or apomorphine; emphasises early identification rather than reserving these for end-stage disease. (See Core §40) [EAN/MDS-ES 2022; Brinker 2024]
• **German Society of Neurology (DGN) — Definition and diagnosis of Parkinson's disease (Hopfner, Höglinger, Trenkwalder, J Neurol Nov 2024): incorporates MDS clinical diagnostic criteria + α-synuclein seed amplification assay** as ancillary biomarker; sets new diagnostic threshold framework. (See Core §3)
• **International cognitive disorders in PD best-practice guidelines (Goldman et al, Age Ageing 2026):** standardises diagnosis and management of mild cognitive impairment in PD and PD-dementia; rivastigmine remains first-line cholinesterase inhibitor; pimavanserin preferred over quetiapine for psychosis in cognitively impaired patients. According to PubMed; [DOI](https://doi.org/10.1093/ageing/afag063) [PMID 41870152]
• **Spanish expert consensus on DA agonist therapy in PD (Mir et al, Neurologia 2023):** practical algorithm for choosing among pramipexole, ropinirole, rotigotine, and apomorphine across early, advanced, and special-population scenarios; emphasises rotigotine patch where swallowing is problematic and apomorphine pump in fluctuating advanced disease. According to PubMed; [DOI](https://doi.org/10.1016/j.nrleng.2023.04.008) [PMID 37419211]
• **MDS-UPDRS Part III meaningful motor progression threshold (Holden et al, J Parkinsons Dis 2025): clinically meaningful threshold estimated at ~3.25 points** OFF-medication; standardises trial endpoint interpretation. According to PubMed; [DOI](https://doi.org/10.1177/1877718X241302337) [PMID 39973477]

RA 6. Indian Regulatory & Society Actions

• Foslevodopa-foscarbidopa (Vyalev / Produodopa) — not yet CDSCO-approved in India as of capture date; AbbVie has stated regulatory submission is in progress for the Indian market (manufacturer communication 2024). The 2024 Indian movement-disorders community has tracked the EU/US approval closely. [AbbVie 2024]
• Apomorphine pump (Apokyn / Apomine) — continues as the only continuous-infusion device-aided therapy widely available in India since the Nanavati launch 2019–20; remains the operational alternative to overseas LCIG/Vyalev for advanced-PD patients in Indian practice.
• Pimavanserin appears in the CDSCO 2024 new-drug approvals list under "Parkinson's disease psychosis" indication; no Indian-manufactured branded form widely available yet — currently imported as Nuplazid. [CDSCO 2024]
• Annals of Indian Academy of Neurology 2023 Supplement (Suppl 1, Vol 26) dedicated issue on PD: multi-modal rehabilitation review, deep brain stimulation outcomes from Indian centres, atypical parkinsonism series — useful Indian-context reference material for thesis citation work.
• ICMR-NCDIR PD epidemiology data (latest 2024 release) estimates Indian PD prevalence at ~70–100 per 100,000, with a younger mean age at onset (~58 years) than Western cohorts — a recurring point in Indian theses. [ICMR 2024]