C. diff Risk


Oral Bioavailability


Approximate Cost

IV$45/d PO$5/d



Serious Infections
(e.g. CNS and Disseminated Zoster)
10mg/kg IV q8h

800mg PO 5 times per day

Prophylaxis dosing varies by indication

General Information

Common Usage

Therapy for herpesviral infections (HSV and VZV) including encephalitis

Prophylaxis of herpesviral infections if recurrent disease or immunocompromised

Drug Monitoring

If IV acyclovir, follow SCr daily; pre-hydration helpful

Check urine for crystals if suspect AKI

Adverse Effects

GI upset, phlebitis, malaise

Increased SCr, AKI from crystal nephropathy (can check urine for acyclovir crystals)

Major Interactions

Concomitant nephrotoxins

Acyclovir may increase serum concentration of clozapine, mycophenolate, zidovudine, tenofovir

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

Pregnancy category: B

Average serum half life: 3.0

Urine penetration: Therapeutic

CSF penetration: Therapeutic