Acyclovir
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Acyclovir
Zovirax
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Summary
Common uses
Genital herpes (HSV-1/2): treatment and suppression0, Herpes labialis (oral/topical)0, Herpes zoster (shingles)0, Varicella in immunocompetent adolescents/adults and immunocompromised0, HSV encephalitis (IV)0, Neonatal HSV (IV)0
Pharmacy
Starting dose
Initial genital herpes 400 mg PO TID × 7-10 days; episodic 800 mg TID × 2 days; suppression 400 mg BID; herpes zoster 800 mg 5×/day × 7 days; HSV encephalitis 10 mg/kg IV q8h × 14-21 days
Preparations
200, 400, 800 mg tablets; 200 mg capsules; 200 mg/5 mL suspension; 500, 1000 mg IV vials; 5% cream and ointment (topical)
US FDA Max
Indication-specific; high-dose IV regimens for encephalitis or disseminated disease
Pharmacology
Routes
Oral, IV, topical
Onset
Symptom relief within 24-48 hours of starting episodic treatment
Duration
8 hours per oral dose
Half-life
~3 hours; significantly prolonged in renal impairment[1]
Bioavailability
~20% (oral; valacyclovir prodrug raises this to ~55%)[1]
Pregnancy
Widely used in pregnancy for HSV/VZV indications; reassuring registry data.[citation needed]
Legal status
Rx-only in US
Purported mechanism
Acyclovir is selectively phosphorylated to acyclovir monophosphate by viral thymidine kinase in HSV/VZV-infected cells, then by host kinases to acyclovir triphosphate, a chain-terminating inhibitor of viral DNA polymerase with markedly higher affinity for the viral than host enzyme.0 The viral-kinase-only initial phosphorylation step is the source of selectivity; uninfected cells generate minimal active drug. Dose-adjust by renal function; rare crystalline nephropathy with rapid IV bolus (slow IV infusion mitigates)[1]. Valacyclovir, the L-valyl ester prodrug, provides higher oral bioavailability and a more convenient dosing schedule for outpatient use.
References
- ↑ 1.0 1.1 1.2 FDA Prescribing Information, Zovirax (acyclovir), GlaxoSmithKline, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2015/018828s041,019909s029,020089s022lbl.pdf