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Antimicrobials

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Acyclovir and Valacyclovir

Guidelines for use

Prescribing for IV acyclovir is restricted to Infectious Diseases

Please click on the titles below to read more:

1. Clinical Uses

  • Herpes simplex virus (HSV) infections
  • Varicella zoster virus (VZV) infections, including varicella and herpes zoster

2. Precautions

  • Acyclovir-resistant HSV: consult Infectious Diseases (prescribing of ganciclovir and foscarnet is restricted)
  • Dosage reductions are required in moderate to severe renal insufficiency
  • Pregnancy: not expected to increase risk of major congenital malformations
  • Breastfeeding: considered safe during breastfeeding. Amounts found in breast milk are lower than the neonatal acyclovir dosage.

3. Adverse Effects

  • Renal failure (crystalline nephropathy) can develop, usually with IV but may occur with PO therapy. Risk factors include: dehydration; pre-existing renal impairment; rapid bolus injection of high doses.
  • CNS toxicity (malaise, lethargy, confusion, delirium) usually in presence of drug accumulation that results in high serum levels, often due to failure to reduce dose in renal insufficiency
  • Nausea and vomiting
  • Phlebitis at site of IV infusion

4. Dosage in Obesity

  • Dosing based on ideal body weight, calculated as follows:
    1. Determine the patient’s actual body weight in kilograms
    2. Determine the patient’s ideal body weight (IBW):
      • IBW (male) = 50.0 kg + 2.3 kg (each inch > 5 feet)
      • IBW (female) = 45.5 kg + 2.3 kg (each inch > 5 feet)
      • 1 inch = 2.5 cm
    3. If patient’s weight is ≥ 30% above their IBW, then patient is obese and ideal body weight should be used for dosing

5. Dosage in Normal Renal Function

Type of Infection and
Immune Status of Patient		 Dosage Recommendations (normal renal function)
IV Acyclovir ORAL Valacyclovir
HSV mucocutaneous infection in
immunocompetent patient		 5 mg/kg q8h 1 g q12h
HSV mucocutaneous infection in
immunocompromised patient		 5 mg/kg q8h 1 g q12h
HSV encephalitis 10 – 15 mg/kg q8h Not applicable
VZV infection regardless
of immune status		 10 – 15 mg/kg q8h 1 g q8h

6. Dosage in Renal Insufficiency

Creatinine Clearance
(mL/min)		 Dosage Recommendations
IV Acyclovir ORAL Valacyclovir
30 to 49 Usual dose q12h Max 2 g per day
(1 g q12h)
10 to 29 Usual dose q24h Max 1.5 g per day
(500 mg q8h)
< 10 (ESRD; PD) 50% of usual dose q24h* Max 1 g q24h*
Hemodialysis (HD)

50% of usual dose q24h*

On dialysis days, give daily dose towards the end of HD. On other days, give dose at same time of day.

Max 1 g q24h*

On dialysis days, give daily dose after HD

Continuous Renal
Replacement Therapy (CRRT)

 Usual dose q12h Use IV acyclovir

*Monitor for CNS toxicity

7. Administration

  • Intermittent Infusion: To reduce the risk of crystalline nephropathy infuse 500mL normal saline prior to acyclovir infusion
  • Please refer to IV drug monograph on pharmacy intranet page for additional administration information.