Dosing and uses of Valtrex (valacyclovir)
Adult dosage forms and strengths
tablet
- 500mg
- 1g
Herpes Labialis
2 g PO q12hr for 1 day
Herpes Zoster
1 g PO q8hr for 7 days (no data on efficacy if started 72 hours after rash)
Genital Herpes
Initial episode: 1 g PO q12hr for 10 days
Recurrent episodes: 500 mg PO q12hr for 3 days (no data on efficacy if started >24 hours after lesion onset)
Suppressive therapy (immunocompetent patients): 1 g/day PO
Suppressive therapy (immunocompetent patients with ≤9 recurrences annually): 500 mg/day PO; transmission reduction for source partner, 500 mg/day PO
Suppressive therapy (HIV-infected patients): 500 mg PO q12hr
Dosing Modifications
Herpes labialis
- CrCl 30-49 mL/min: 1 g PO q12hr for 1 day
- CrCl 10-29 mL/min: 500 mg PO q12hr for 1 day
- CrCl <10 mL/min: 500 mg PO once
Herpes zoster
- CrCl 30-49 mL/min: 1 g PO q12hr
- CrCl 10-29 mL/min: 1 g/day PO
- CrCl <10 mL/min: 500 mg/day PO
Genital herpes (initial episode)
- CrCl 10-29 mL/min: 1 g/day PO
- CrCl <10 mL/min: 500 mg/day PO qDay
Genital herpes (recurrent episodes)
- CrCl ≤29 mL/min: 500 mg/day PO
Genital herpes (suppressive therapy, immunocompetent patients)
- CrCl ≤29 mL/min: 500 mg/day PO
Genital herpes (suppressive therapy, immunocompetent patients with ≥9 recurrences annually)
- CrCl ≤29 mL/min: 500 mg PO q48hr
Genital herpes (suppressive therapy, HIV-infected patients)
- CrCl ≤29 mL/min: 500 mg/day PO
Pediatric dosage forms and strengths
tablet
- 500mg
- 1g
Chickenpox
<2 years: Safety and efficacy not established
>2 years: 20 mg/kg PO q8hr for 5 days; not to exceed 1 g PO q8hr
Herpes Labialis
<12 years: Safety and efficacy not established
>12 years: 2 g PO q12hr for 1 day
Geriatric dosage forms and strengths
Monitor renal function; dosage may have to be adjusted, depending on renal status
Valtrex (valacyclovir) adverse (side) effects
>10%
Headache (14-35%)
Neutropenia (<18%)
Elevated aspartate transaminase (AST) (2-16%)
Nasopharyngitis (<16%)
Nausea (6-15%)
Elevated alanine transaminase (ALT) (<14%)
Abdominal pain (2-11%)
1-10%
Dysmenorrhea (1-8%)
Depression (<7%)
Arthralgia (<1-6%)
Vomiting (<1-6%)
Dizziness (2-4%)
Rash (≤8%)
Rhinorrhea (<2%)
Thrombocytopenia (<3%)
Leukopenia (≤1%)
<1%
Agitation
Aggression
Alopecia
Confusion
Erythema multiforme
Hypertension
Tachycardia
Tremor
Visual disturbances
Warnings
Contraindications
Hypersensitivity to valacyclovir or acyclovir
Cautions
Thrombotic thrombocytopenic purpura (TTP)/hemolytic uremic syndrome (HUS) reported in patients with advanced HIV disease and in allogenic bone marrow transplant and renal transplant recipients
Acute renal failure (ARF) may occur, especially in elderly patients or those with underlying renal impairment receiving higher than recommended doses; use with caution in patients with renal impairment, the elderly, and/or patients receiving nephrotoxic drugs
Treatment should begin with the earliest symptom (tingling, burning, itching) in cold sores; for genital herpes, it should begin at the first signs and symptoms (within 72 hours of onset of first diagnosis or 24 hours of onset of recurrent episodes); for herpes zoster, it should begin within 72 hours of onset of rash; for chicken pox, it should begin with the earliest sign or symptom
Central nervous system (CNS) effects may occur (eg, agitation, hallucinations, confusion, encephalopathy); risk of CNS adverse effects is higher in elderly patients
Adequately hydrate patient; decreased precipitation in renal tubules may occur
Pregnancy and lactation
Pregnancy category: B
Lactation: Drug excreted in breast milk; use with caution
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of Valtrex (valacyclovir)
Mechanism of action
Converted to acyclovir by intestinal and hepatic metabolism
Competes with deoxyguanosine triphosphate for viral DNA polymerase to inhibit DNA synthesis and viral replication
Absorption
Rapidly absorbed
Bioavailability: ~55% (after conversion to acyclovir)
Distribution
Acyclovir (active drug) is widely distributed throughout the body, including brain, kidney, muscle, uterus, lungs, liver, spleen, vagina, and cerebrospoinal fluid (CSF)
Protein bound: 13.5-17.9%
Metabolism
Metabolized by liver; valacyclovir is rapidly and nearly completely converted to acyclovir and L-valine via first-pass effect; acyclovir is hepatically metabolized to a very small extent by aldehyde oxidase and by alcohol and aldehyde dehydrogenase (inactive metabolites)
Elimination
Half-life (normal renal function, adults): Acyclovir, 2.5-3.3 hr; valacyclovir, ~30 min
Half-life (end-stage renal disease): Acyclovir, 14-20 hr
Excretion: Urine (89%), feces (minimal)
