C. diff Risk


Oral Bioavailability


Approximate Cost

IV$45/d PO$5/d



Renally cleared, requires dosage adjustment with changes in renal function. Consult a pharmacist for renal dosing.

General Information

Common Usage

  • Therapy for herpes virus infections (HSV and VZV) including encephalitis

  • Prophylaxis of herpes virus infections if recurrent disease or immunocompromised

Drug Monitoring

  • Follow creatinine, urea, urine output as appropriate, liver enzymes and CBC.

  • BUN/Creatinine and fluid balance must be monitored daily in patients receiving high dose acyclovir. Ensure adequate hydration during and for at least 2 hours following administration. Manufacturer suggests 1 litre of fluid/24 hours/gram of acyclovir and recommends a minimum urine output of 500 mL/24 hours/gram of acyclovir.

Adverse Effects

  • Nausea

  • Vomiting

  • Diarrhea

  • Headache

  • Phlebitis (IV)

  • Liver or renal dysfunction

  • Crystal nephropathy (keep patient well hydrated)

Major Interactions

  •  May diminish efficacy of zoster or varicella vaccine

Additional Information

  •  For oral indications, Valacyclovir is the pro-drug and is more bioavailable with more convenient dosing.


Antimicrobial class: Antiviral, nucleoside analogue

Route of Elimination: Primarily kidney with 60-90% of drug excreted unchanged in the urine

Average serum half life: Neonates: 4 hours
Children 1-12 years: 2-3 hours