Antimicrobials
Valacyclovir

Valacyclovir

None
Excellent

Spectrum of Activity

Dosing

General Information

For genital herpes, treatment should begin as soon as possible after the first signs and symptoms (within 72 hours of onset of first diagnosis or within 24 hours of onset of recurrent episodes).

Treatment of herpes zoster (shingles) in immunocompetent patients.

Treatment of first-episode and recurrent genital herpes in immunocompetent patients.

Suppression of recurrent genital herpes and reduction of transmission of genital herpes in immunocompetent patients.

Suppression of genital herpes in patients with HIV.

Treatment of herpes labialis (cold sores).

Treatment of chickenpox in immunocompetent children.

Laboratory

  • BMP
  • CBC

Clinical

  • As a prodrug of acyclovir, valacyclovir may also cause acute kidney injury (Ref)
  • Similar to acyclovir, this may result most often from renal disease (obstructive nephropathy) but may also be due to interstitial nephritis or renal tubular necrosis
  • Kidney injury is reversible in most cases after dosage reduction or discontinuation
  • Typically occurred within 5 days of initiation
  • N/V
  • Rash
  • Abdominal pain
  • CNS manifestations: tremor, agitation, confusion, hallucinations

Substrate of OCT1; Inhibits CYP1A2 (weak)

Clozapine: may increase clozapine concentrations

Foscarnet: may enhance nephrotoxic effect of acyclovir and valacylovir (avoid)

Mycophenolate: may increase mycophenolate concentrations

Tizanidine: may increase tizanidine concentrations

Varicella Virus Vaccine: Acyclovir/valacyclovir may diminish the therapeutic effect of Varicella Virus Vaccine

  • When possible, avoid use of acyclovir or valacyclovir within the 24 hours prior to administration of the varicella vaccine, and avoid use of these antiviral agents for 14 days after vaccination

Zoster Vaccine (Live/Attenuated): Acyclovir/valacyclovir may diminish the therapeutic effect of Zoster Vaccine

Pro-drug of acyclovir with improved absorption and more convenient dosing compared to oral acyclovir.

Antimicrobial class: Antiviral - Synthetic Guanine Analog

Pregnancy category: B

Absorption: Rapid.

Distribution: Acyclovir is widely distributed throughout the body including brain, kidney, lungs, liver, spleen, muscle, uterus, vagina, and CSF.

Protein binding: Valacyclovir: 13.5% to 17.9%; Acyclovir: 9% to 33%.

Metabolism: Hepatic; valacyclovir is rapidly and nearly completely converted to acyclovir and L-valine by first-pass effect; acyclovir is hepatically metabolized to a very small extent by aldehyde oxidase and by alcohol and aldehyde dehydrogenase (inactive metabolites).

Bioavailability: Tablet: 54.5% ± 9.1%.

Half-life elimination: Acyclovir: normal renal function: average 3 hours; valacyclovir: ~30 minutes; End-stage renal disease: 14 to 20 hours; During hemodialysis: 4 hours.

Time to peak: 1.5 hours.

Excretion: Urine, primarily as acyclovir (89%)