What is the recommended dosage and frequency of Valtrex (valacyclovir) for a patient with a viral infection, such as herpes simplex or herpes zoster, considering factors like severity of symptoms, medical history, and impaired renal function?

Valtrex (Valacyclovir) Dosage and Frequency

The recommended dosage of Valtrex varies significantly by indication: for herpes zoster (shingles), use 1 gram three times daily for 7 days; for recurrent genital herpes, use 500 mg twice daily for 3 days; and for cold sores, use 2 grams twice daily for 1 day only. 1

Herpes Zoster (Shingles) Dosing

Standard Regimen for Immunocompetent Patients

• Valacyclovir 1 gram orally three times daily for 7 days is the FDA-approved dosage for herpes zoster 1
• Therapy must be initiated within 72 hours of rash onset for optimal efficacy in reducing acute pain, accelerating lesion healing, and preventing postherpetic neuralgia 2
• Continue treatment until all lesions have completely scabbed, not just for an arbitrary 7-day period—this is the key clinical endpoint 2

Alternative Dosing Considerations

• Valacyclovir 1.5 grams twice daily for 7 days has been shown to be as safe and effective as the three-times-daily regimen, with the advantage of improved compliance 3
• The twice-daily regimen may be particularly useful when adherence is a concern 3

Immunocompromised Patients

• Switch to intravenous acyclovir 10 mg/kg every 8 hours for disseminated or invasive herpes zoster, severely immunocompromised patients, CNS complications, or complicated ocular disease 2
• Continue IV therapy for a minimum of 7-10 days and until clinical resolution (all lesions scabbed) 2
• Consider temporary reduction in immunosuppressive medications in cases of disseminated disease 2

Genital Herpes Dosing

Initial Episode

• Valacyclovir 1 gram twice daily for 10 days for first-episode genital herpes 1
• Most effective when started within 48 hours of symptom onset 1
• May extend treatment if healing is incomplete after 10 days 4

Recurrent Episodes

• Valacyclovir 500 mg twice daily for 3 days for recurrent genital herpes 1
• Initiate treatment at the first sign or symptom of an episode 1
• Patients should keep medication on hand to enable immediate self-initiation at prodrome onset 5

Suppressive Therapy

• Valacyclovir 1 gram once daily for patients with normal immune function 1
• Alternative dose: 500 mg once daily for patients with 9 or fewer recurrences per year 1
• For HIV-infected patients with CD4+ count ≥100 cells/mm³: 500 mg twice daily 1
• Suppressive therapy reduces recurrence frequency by ≥75% and is safe for extended use 5

Cold Sores (Herpes Labialis) Dosing

• Valacyclovir 2 grams twice daily for 1 day only (two doses taken 12 hours apart) 1
• Therapy must be initiated at the earliest symptom (tingling, itching, or burning) 1
• This single-day regimen is specifically designed for cold sores and should not be confused with longer courses for other indications 1

Renal Impairment Dosing Adjustments

Dose adjustments are mandatory for patients with impaired renal function to prevent acute renal failure 2

Herpes Zoster Adjustments

• CrCl 30-49 mL/min: 1 gram every 12 hours 1
• CrCl 10-29 mL/min: 1 gram every 24 hours 1
• CrCl <10 mL/min: 500 mg every 24 hours 1

Genital Herpes (Recurrent) Adjustments

• CrCl 10-29 mL/min: 500 mg every 24 hours 1
• CrCl <10 mL/min: 500 mg every 24 hours 1

Hemodialysis Patients

• Administer the recommended dose after hemodialysis 1
• Approximately one-third of acyclovir is removed during a 4-hour hemodialysis session 1

Critical Timing Considerations

• Treatment is most effective when initiated within 48-72 hours of symptom onset for all indications 2, 1
• For herpes zoster, the 72-hour window is the maximum timeframe for optimal efficacy 2
• For cold sores and recurrent genital herpes, earlier initiation during prodrome provides maximum benefit 5, 1

Important Clinical Pitfalls and Caveats

Avoid These Common Errors

• Never use topical acyclovir or valacyclovir—it is substantially less effective than systemic therapy and is not recommended 2, 5
• Do not use short-course genital herpes regimens for herpes zoster—VZV requires longer treatment duration 2
• Do not stop treatment at exactly 7 days if lesions are still forming or have not completely scabbed—continue until all lesions have crusted 2

High-Dose Toxicity Warning

• Avoid valacyclovir doses of 8 grams per day in immunocompromised patients due to risk of thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS) 4, 6
• This complication has been reported with prolonged high-dose therapy, particularly in patients with advanced HIV disease 6

Monitoring Requirements

• Monitor renal function closely during therapy, especially with IV acyclovir 2
• Assess for TTP/HUS in immunocompromised patients receiving high-dose therapy 2
• If lesions fail to resolve within 7-10 days, suspect acyclovir resistance and obtain viral culture with susceptibility testing 2

Treatment Failure and Resistance

• If lesions persist despite appropriate valacyclovir treatment, consider HSV or VZV resistance 4
• All acyclovir-resistant strains are also resistant to valacyclovir 2, 4
• For confirmed acyclovir-resistant infections: IV foscarnet 40 mg/kg every 8 hours until clinical resolution 2, 4

Administration Guidelines

• Valtrex may be given without regard to meals 1
• For pediatric patients requiring liquid formulation, an oral suspension (25 mg/mL or 50 mg/mL) can be prepared extemporaneously from 500-mg tablets 1
• The prepared suspension must be stored refrigerated (2-8°C) and discarded after 28 days 1