Acyclovir

Antiviral activity

Purine nucleoside analogue with in vitro and in vivo inhibitory activity against herpes simplex virus (HSV-1,HSV-2), and varicella-zoster virus (VZV). In cell culture, acyclovir's highest antiviral activity is against HSV-1, followed in decreasing order of potency against HSV-2 and VZV.

Pregnancy Risk Factor

Class C

Contraindication/Precaution

Hypersensitivity to acyclovir,  or any component
Use caution with nursing mothers
Use caution if renal dysfunction or if other nephrotoxic agents present
Safety and effectiveness in pediatric patients less than two years of age have not been adequately studied.

Mechanism of Action

Inhibits DNA synthesis and viral replication by competing with deoxyguanosine triphosphate for viral DNA polymerase and being incorporated into viral DNA.

Pharmacodynamics

Metabolism: N/A
Half-life: 2.5-3.3 hours, changes with renal function
Elimination: excreted in urine

Dosage

Children: (max 800 mg/d or 80 mg/kg/day)

>2 years old: 
acute varicella: 10-20 mg/kg PO  5x/day or 10 mg/kg IV q8h
herpes zoster: 10-16 mg/kg PO 5x/day or 10 mg/kg IV q8h

Adults and children >40 kg:

Genital herpes, 1 episode:
200 mg PO 5x/day for 10 days
Genital herpes, recurrent:
200 mg PO 5x/day for 5 days
Genital herpes, suppressive:
400 mg PO bid
Herpes zoster:
800 mg PO 5x/day for 7-10 days
HSV infections:
5-10 mg /kg IV q8h for 7 days
Acute Varicella:
800 mg PO qid for 5 days

Dose VS renal function

Cr. clearance (ml/min):
<10: PO normal dose but q12h, IV 2.5-5 mg/kg q24h 10-25:  PO normal dose but q8h, IV 5-10 mg/kg q24h >25: PO unchanged, IV 5-10 mg/kg q12h

Dialysis
Hemo: adjusted dosing schedule so that an additional dose is administered post dialysis
CAPD: PO  normal dose but q12h, IV 2.5-5 mg/kg q24h