C. diff Risk


Oral Bioavailability


Approximate Cost


  • Use ideal body weight for dosing obese patients (BMI ≥30 kg/m2)

5-10 mg/kg IV every 8 hr

Consider higher dosing for serious infections such as CNS and disseminated zoster
10mg/kg IV every 8 hr

800 mg 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


  • Follow SCr as appropriate

  • Check urine for crystals if AKI suspected

  • Ensure adequate hydration for the patient

  • Phlebitis (with IV formulation)


  • CNS effects

  • Ensure adequate hydration for the patient

  • Phlebitis (with IV formulation)

Adverse Effects

  •  GI upset

  •  Phlebitis/Extravasation

  •  Increased SCr

  •  AKI from crystal nephropathy
    CNS Effects (confusion, tremor, lethargy, hallucination)

Major Interactions

Mycophenolate can increase the acyclovir concentration

May diminish efficacy of zoster or varicella vaccine

Additional Information

For oral indications, valacyclovir is the pro-drug, which is more bioavailable with more convenient dosing.


Antimicrobial class: Antiviral. Nucleoside analogue.

Pregnancy category: B

Average serum half life: 3 hours

CSF penetration: Therapeutic

Urine penetration: Therapeutic