What is the recommended valacyclovir (Valtrex) dosage for treating herpes zoster and herpes simplex, considering impaired renal function?

Valacyclovir Dosing Recommendations

Herpes Zoster (Shingles)

For herpes zoster in immunocompetent adults, administer valacyclovir 1000 mg orally three times daily for 7 days, initiated within 48-72 hours of rash onset for maximum efficacy. 1

• Treatment is most effective when started within 48 hours of rash onset, though benefit may still occur when initiated later 2, 1
• The 7-day regimen is as effective as 14-day treatment, making the shorter course preferable 1
• For immunocompromised patients or persistent/recalcitrant disease, consider valacyclovir 1000 mg every 8 hours for 7 days 3

Renal Dose Adjustments for Herpes Zoster

• CrCl 30-49 mL/min: 1000 mg every 12 hours 1
• CrCl 10-29 mL/min: 1000 mg every 24 hours 1
• CrCl <10 mL/min: 500 mg every 24 hours 1
• Hemodialysis patients: Administer the recommended dose after hemodialysis; approximately one-third of acyclovir is removed during a 4-hour session 1
• Peritoneal dialysis: No supplemental dosing required after CAPD or CAVHD 1

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Herpes Simplex Virus (HSV) Infections

Initial Genital Herpes Episode

For first-episode genital herpes, prescribe valacyclovir 1000 mg orally twice daily for 10 days, starting within 48 hours of symptom onset. 2, 4, 1

• Treatment may be extended beyond 10 days if healing is incomplete 4
• Note that 5-30% of first-episode genital herpes is caused by HSV-1, which has less frequent recurrences than HSV-2 4

Recurrent Genital Herpes Episodes

• Standard episodic treatment: Valacyclovir 500 mg orally twice daily for 3 days 2, 1
• Patients should initiate treatment at the first sign of prodrome or lesions for maximum benefit 2, 1
• Provide medication or prescription in advance to enable immediate self-initiated treatment 2

Suppressive Therapy for Recurrent Genital Herpes

• Immunocompetent patients: Valacyclovir 1000 mg once daily 2, 1
  • Alternative for patients with ≤9 recurrences per year: 500 mg once daily 1
• HIV-infected patients (CD4+ ≥100 cells/mm³): Valacyclovir 500 mg twice daily 4, 1
• Suppressive therapy reduces recurrence frequency by ≥75% but does not eliminate asymptomatic viral shedding 2

Renal Dose Adjustments for Genital Herpes

Recurrent episodes:

• CrCl 30-49 mL/min: No reduction needed 1
• CrCl 10-29 mL/min: 500 mg every 24 hours 1
• CrCl <10 mL/min: 500 mg every 24 hours 1

Suppressive therapy (immunocompetent, 1 g daily regimen):

• CrCl 30-49 mL/min: No reduction needed 1
• CrCl 10-29 mL/min: 500 mg every 24 hours 1
• CrCl <10 mL/min: 500 mg every 24 hours 1

Suppressive therapy (500 mg daily regimen for ≤9 recurrences/year):

• CrCl 30-49 mL/min: No reduction needed 1
• CrCl 10-29 mL/min: 500 mg every 48 hours 1
• CrCl <10 mL/min: 500 mg every 48 hours 1

Cold Sores (Herpes Labialis)

• Adults and adolescents ≥12 years: Valacyclovir 2000 mg twice daily for 1 day (two doses 12 hours apart) 1
• Initiate at the earliest symptom (tingling, itching, or burning) 1

Renal adjustments for cold sores:

• CrCl 30-49 mL/min: No reduction needed 1
• CrCl 10-29 mL/min: 1000 mg every 24 hours 1
• CrCl <10 mL/min: 500 mg every 24 hours 1
• Do not exceed 1 day of treatment 1

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Severe HSV or VZV Disease Requiring Hospitalization

For severe disease with complications (disseminated infection, pneumonitis, hepatitis, CNS involvement), use IV acyclovir 5-10 mg/kg every 8 hours for 5-7 days or until clinical resolution instead of oral valacyclovir. 5, 2, 4

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Critical Clinical Considerations

Immunocompromised Patients

• Higher doses or longer treatment duration may be necessary 3
• Avoid valacyclovir doses of 8 grams per day in immunocompromised patients due to risk of thrombotic thrombocytopenic purpura/hemolytic uremic syndrome 5, 4
• For HIV-infected patients with severe or prolonged episodes, consider acyclovir 400 mg orally 3-5 times daily 5

Treatment Failure and Resistance

• If lesions persist despite appropriate valacyclovir treatment, suspect HSV resistance 4
• All acyclovir-resistant HSV strains are also resistant to valacyclovir 5, 4
• For acyclovir-resistant HSV, use IV foscarnet 40 mg/kg every 8 hours until clinical resolution 5, 4

Pediatric Dosing

• Chickenpox (ages 2 to <18 years): 20 mg/kg three times daily for 5 days (maximum 1000 mg per dose) 1
• Cold sores (≥12 years): Same as adult dosing 1
• Data are not available for pediatric patients with CrCl <50 mL/min/1.73 m² 1

Important Timing Considerations

• Therapy is most effective when initiated within 48 hours of symptom onset for both HSV and VZV 2, 1
• For recurrent HSV, treatment at prodrome provides maximum benefit 2
• Valacyclovir may be given without regard to meals 1