COVID-19 Pharmacotherapy

COVID-19 Pharmacotherapy

1. Definition, virology & rationale for pharmacotherapy

• COVID-19 (CO-rona VI-rus D-isease) is the clinical syndrome caused by SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2), named by the WHO in February 2020; the outbreak began in late 2019 in Wuhan, China, and became a worldwide pandemic (G&G 14e Ch.62, p.1223).
• SARS-CoV-2 belongs to the β-coronavirus genus, the same family that contains SARS-CoV (2003) and MERS-CoV (Middle East respiratory syndrome coronavirus); it is an enveloped, positive-sense single-stranded RNA (+ssRNA) virus with a large (~30 kb) genome (G&G 14e Ch.62, p.1223).
• As a +ssRNA virus, its genomic RNA serves directly as mRNA; it is translated into a polyprotein that is proteolytically cleaved by viral proteases into non-structural proteins, including the RNA-dependent RNA polymerase (RdRp, nsp12) that directs synthesis of new viral RNA — most RNA viruses complete replication in the host-cell cytoplasm (G&G 14e Ch.62, p.1211).
• Key structural proteins: spike (S) glycoprotein (mediates ACE2-receptor binding + host-cell entry; the target of neutralising antibodies and vaccines), envelope (E), membrane (M), nucleocapsid (N) (G&G 14e Ch.62, p.1223).
• Two pharmacologically distinct therapeutic windows define the entire treatment strategy:
  • Early viral-replication phase (first ~5–7 days, mild/non-severe disease) → antivirals that block replication have maximal benefit; "to be effective, therapy has to be started in the incubation period... or pre-emptive," because in acute viral infections replication peaks as symptoms appear (KDT 8e Ch.59, p.849).
  • Late host-inflammatory (hyperinflammatory) phase (after ~7 days, severe/critical disease, often hypoxaemic) → the pathology is driven by a dysregulated immune response ("cytokine storm"), so anti-inflammatory immunomodulators (corticosteroids, IL-6 blockers, JAK inhibitors), not antivirals, drive mortality benefit [WHO living guideline] [NIH].
• This biphasic model is the single most important MD-level concept: the right drug at the wrong stage is useless or harmful (e.g. dexamethasone helps the hypoxaemic patient but worsens survival in the non-oxygen-requiring patient) [PMID 32678530 — RECOVERY].
• General antiviral-pharmacology principle underpinning all SARS-CoV-2 antivirals: viruses are obligate intracellular parasites that hijack host machinery, so selective toxicity requires targeting virus-specific steps — cell penetration/uncoating, the viral polymerase, or virus-specific proteases (KDT 8e Ch.59, p.849; G&G 14e Ch.62, p.1211).