Pharm 101: Aciclovir


Antiviral agent

  • Guanosine derivative with activity against HSV-1 and HSV-2, and VZV (10x less potent)
  • In vitro activity against EBV, CMV and HHV-6 is present but weaker
  • Inhibits viral DNA synthesis
    • Selectively activated in virus cells by virus-specific thymidine kinase (three phosphorylation steps for activation)
    • Irreversibly binds to viral DNA polymerase
    • Incorporation into viral DNA with termination
  • Absorption unaffected by food
  • Low bioavailability 15-20%
  • Widely distributed
  • CSF concentrations 20-50% of serum values
  • Half-life 2-3 hours in normal renal function (5x daily dosing oral)
  • Renal clearance, mostly excreted unchanged in urine
Clinical uses
  • HSV encephalitis
  • Serious HSV or VZV infections
  • Immunocompromised patients with VZV
  • Topical administration for primary HSV infection (genital herpes)
Adverse effects
  • GI upset: nausea, vomiting, diarrhoea
  • Headache
  • IV infusion is associated with reversible renal toxicity or neurological effects (tremor, delirium, seizures)
  • Concurrent administration of nephrotoxic agents may enhanced potential for nephrotoxicity

Pharmacology 101

Top 200 drugs

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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