What is the recommended dosage of valacyclovir (Valtrex) for treating herpes simplex virus or varicella-zoster virus flare-ups?

Valacyclovir Dosing for Viral Flare-Ups

For herpes simplex virus (HSV) recurrent episodes, valacyclovir 500 mg twice daily for 5 days is the recommended treatment, initiated at the first sign of prodrome or lesions. 1

HSV Genital Herpes Recurrent Episodes

Episodic Treatment Options:

• Valacyclovir 500 mg orally twice daily for 5 days (preferred for convenience) 1
• Alternative: Valacyclovir 1000 mg once daily for 5 days 2
• Treatment must be initiated at the first sign of prodrome or genital lesions for maximum efficacy 1
• Patients should be provided with medication or a prescription in advance to enable immediate treatment initiation 1

Suppressive Therapy (for frequent recurrences ≥6 per year):

• Valacyclovir 1000 mg once daily for patients with normal immune function 1, 2
• Alternative: Valacyclovir 500 mg once daily for patients with ≤9 recurrences per year 1, 2
• Suppressive therapy reduces recurrence frequency by ≥75% 1
• Safety and efficacy documented for valacyclovir for 1 year of continuous use 1

HSV in Immunocompromised Patients

HIV-infected patients with CD4+ ≥100 cells/mm³:

• Valacyclovir 500 mg twice daily for suppressive therapy 2
• Higher doses may be necessary due to more severe and frequent recurrences 3
• Critical warning: Avoid valacyclovir doses of 8 grams per day in immunocompromised patients due to risk of thrombotic thrombocytopenic purpura/hemolytic uremic syndrome 3, 4

Treatment-resistant HSV:

• If lesions persist despite appropriate valacyclovir treatment, suspect acyclovir resistance 3
• All acyclovir-resistant HSV strains are also resistant to valacyclovir 3
• For confirmed resistance: IV foscarnet 40 mg/kg every 8 hours until clinical resolution 3

Herpes Zoster (Shingles) Flare-Ups

Standard Treatment:

• Valacyclovir 1000 mg orally three times daily for 7 days 2
• Therapy must be initiated within 48 hours of rash onset for maximum effectiveness 2
• Treatment is most effective when started at the earliest sign or symptom 2

Severe or Persistent Disease:

• For persistent or recalcitrant disease in immunocompetent patients: Valacyclovir 1000 mg every 8 hours for 7 days 5, 6
• For immunocompromised patients: Higher doses or longer treatment duration may be necessary, with infectious disease consultation recommended 5, 6

Severe Disease Requiring Hospitalization

For any severe HSV or VZV infection with complications:

• IV acyclovir 5-10 mg/kg every 8 hours for 5-7 days or until clinical resolution 1, 6
• Indications include disseminated infection, pneumonitis, hepatitis, or CNS complications (meningitis, encephalitis) 1
• Immunosuppressive therapy should be discontinued in severe varicella infection or disseminated HSV/VZV 1

Renal Impairment Dosing Adjustments

Critical dosing modifications required:

• Creatinine clearance 30-49 mL/min: No reduction for recurrent genital herpes (500 mg every 12 hours); for herpes zoster, reduce to 1000 mg every 12 hours 2
• Creatinine clearance 10-29 mL/min: Genital herpes 500 mg every 24 hours; herpes zoster 1000 mg every 24 hours 2
• Creatinine clearance <10 mL/min: Genital herpes 500 mg every 24 hours; herpes zoster 500 mg every 24 hours 2
• Hemodialysis patients: Administer recommended dose after hemodialysis session 2

Important Clinical Considerations

Treatment timing is critical:

• Therapy is most effective when initiated within 48 hours of symptom onset for both HSV and VZV 1, 2
• For recurrent HSV, treatment at prodrome (tingling, itching, burning) provides maximum benefit 1

Transmission risk:

• Suppressive therapy reduces but does not eliminate asymptomatic viral shedding 1, 3
• Patients should be counseled that transmission can occur even during asymptomatic periods 1

HSV-1 vs HSV-2 distinction:

• 5-30% of first-episode genital herpes cases are caused by HSV-1 1, 3
• HSV-1 genital infections have much less frequent clinical recurrences than HSV-2, which has important prognostic implications 1, 3