Aldose Reductase Inhibitors & Diabetic Neuropathy

Aldose Reductase Inhibitors & Diabetic Neuropathy

1. Scope, exam framing, and the one-line answer

• Epalrestat is the RGUHS-examinable face of this topic: it appears as a standalone 10-mark question in Paper III (Jul 2023 and Dec 2023), so this account is deliberately built around the drug, with polyol-pathway biochemistry as its mechanistic scaffold and diabetic peripheral neuropathy (DPN) as its clinical arena.
• The one-line answer: epalrestat is an orally active, reversible, non-competitive, selective inhibitor of aldose reductase (AR, AKR1B1) — the rate-limiting first enzyme of the polyol pathway — used at 50 mg three times daily before meals as a pathogenesis-oriented (disease-modifying) rather than symptom-suppressing treatment for diabetic peripheral neuropathy. (KDT 8e Ch.19, p.303) [PMID 37971280]
• The examinable contrast that gives this topic its shape: every other drug used in painful DPN — pregabalin, gabapentin, duloxetine, amitriptyline, capsaicin — treats the symptom; epalrestat targets the lesion. Symptomatic analgesic monotherapy relieves the pain without touching the underlying neuropathy, has limited efficacy and carries adverse events — the stated "unmet need" that pathogenesis-oriented agents exist to fill. [PMID 38245327]
• A second examinable contrast: the aldose-reductase-inhibitor class is largely a graveyard, and epalrestat is its single clinical survivor. ARIs "when first introduced were proclaimed to be major advances in treating diabetic complications, [but] have never produced the expected results"; problems with efficacy and toxicity "relegated most of this class of agents to historical interest". [PMID 8329799] Epalrestat is described in 2019 as "the only antidiabetic aldose reductase inhibitor approved for use in humans". [PMID 31636082]
• Scope boundaries for this topic: in scope — the polyol/sorbitol pathway, aldose reductase as a target, the ARI class, epalrestat in depth, the ADCT/Hotta evidence, and the place of ARIs alongside glycaemic control and symptomatic agents in DPN. Out of scope — general antidiabetic pharmacology (insulins, sulfonylureas, metformin, DPP-4/SGLT-2/GLP-1 agents), which is a separate topic even though the same textbook chapters cover it.
• Terminology to keep straight from the outset: aldose reductase = AR = ALR2 = AKR1B1, an aldo-keto reductase; AKR1B10 is its closely related paralogue (relevant to epalrestat's oncology repurposing); SORD = sorbitol dehydrogenase, the second enzyme of the same two-step pathway. [PMID 35964660] [PMID 39017606] (Harrison 21e Ch.457, p.3601)
• Nomenclature note for Indian practice: epalrestat is marketed in India as ALRISTA 50 mg tablet; there is no separate Indian generic naming convention for the molecule. (KDT 8e Ch.19, p.303)
• Register of evidence quality up front, because the examiner will probe it: KDT's own verdict is that epalrestat "has caused modest improvement in nerve conduction, neuropathic pain and other symptoms" but that "magnitude of benefit and safety are yet to be defined". (KDT 8e Ch.19, p.303) Bradley is blunter — trials of ARIs "have so far failed to produce convincing clinical improvement or proved toxic, though there were modest changes in nerve conduction and nerve pathology". (Bradley 8e Ch.106, p.1908) These verdicts are reconciled against the ADCT data in §14 and §18 and flagged in the multi-source disagreements appendix.