Class: Viral DNA Polymerase Inhibitor
Dosage Forms. Tablet: 500 mg, 1000 mg
Common FDA Label Indication, Dosing, and Titration.
1. Genital herpes simplex: Initial episode, 1 g po bid × 7-10 d
2. Genital herpes simplex: Suppressive therapy, 1 g po daily
3. Herpes zoster, shingles: 1 g tid × 7-10 d
4. Varicella: Peds 2 y and older, 20 mg/kg po tid × 5 d
Off-Label Uses.
1. Genital herpes simplex—HIV infection: (initial or recurrent) 1 g bid × 5-14 d
MOA. Valacyclovir is a prodrug of acyclovir. Acyclovir is an acyclic nucleoside analogue of deoxyguanosine that is selectively phosphorylated by the virus-encoded thymidine kinase to its monophosphate form. Cellular enzymes then convert the monophosphate to the active antiviral acyclovir triphosphate, which inhibits viral DNA synthesis by incorporation into viral DNA, resulting in chain termination. Acyclovir has potent activity against herpes simplex virus (HSV) I and II and varicella-zoster virus (VZV).
Drug Characteristics: Valacyclovir
Medication Safety Issues: Valacyclovir
Drug Interactions: Valacyclovir
Adverse Reactions: Valacyclovir
Efficacy Monitoring Parameters. Resolution of clinical signs of infection (lesions) within 2-3 d.
Toxicity Monitoring Parameters. Seek medical attention if decreased urination, unusual bruising or bleeding, blistering skin rash, or shortness of breath Monitor CBC, LFTs, SCr.
Key Patient Counseling Points. Symptoms should improve within 2-3 d; if they worsen, seek follow-up with healthcare practitioner. If using for prophylaxis, this medication should reduce the number of breakouts.
Clinical Pearls. Not indicated for children <2 y of age. Use caution with concurrent nephrotoxins. Not for use in adults with chicken pox (varicella). Drug of choice for herpes zoster infection. Improved oral bioavailability over acyclovir, allowing BID dosing of valacyclovir (compared to 5 times per day dosing of acyclovir).