What is the recommended dosage and treatment duration of Aciclovir (antiviral medication) for herpes simplex virus infections and varicella zoster?

Aciclovir Dosage and Treatment Regimens for Herpes Simplex and Varicella Zoster Infections

For herpes simplex virus infections, oral aciclovir should be dosed at 200 mg 5 times daily for 7-10 days for initial episodes, while varicella zoster (shingles) requires 800 mg 5 times daily for 7-10 days. 1, 2

Herpes Simplex Virus (HSV) Infections

Initial Genital Herpes Episodes

• First clinical episode: 200 mg orally 5 times daily (every 4 hours) for 7-10 days or until clinical resolution 2, 1
• First episode of herpes proctitis: 400 mg orally 5 times daily for 10 days or until clinical resolution 2

Recurrent Genital Herpes

• Treatment is most effective when initiated within 24-48 hours of symptom onset 2
• Options include:
  • 200 mg orally 5 times daily for 5 days
  • 400 mg orally 3 times daily for 5 days
  • 800 mg orally 2 times daily for 5 days 2, 1

Suppressive Therapy for Recurrent HSV

• Indicated for patients with ≥6 recurrences per year 2
• Recommended regimen: 400 mg orally twice daily for up to 12 months 1
• Alternative regimen: 200 mg orally 3-5 times daily 2, 1
• After 1 year of therapy, reassess frequency and severity of infections 1

Varicella Zoster Virus (VZV) Infections

Herpes Zoster (Shingles)

• Standard regimen: 800 mg orally 5 times daily (every 4 hours) for 7-10 days 1, 2
• Treatment should be initiated within 72 hours of rash onset for optimal efficacy 2
• High-dose IV aciclovir remains the treatment of choice for VZV infections in immunocompromised hosts 2

Chickenpox (Varicella)

• Children (2 years and older): 20 mg/kg per dose orally 4 times daily (maximum 80 mg/kg/day) for 5 days 1
• Adults and children >40 kg: 800 mg orally 4 times daily for 5 days 1
• Treatment should be initiated at the earliest sign or symptom 1

Special Populations

Immunocompromised Patients

• Severe HSV disease: Intravenous aciclovir 5-10 mg/kg body weight every 8 hours for 5-7 days or until clinical resolution 2
• VZV infections: High-dose IV aciclovir is recommended 2
• HIV-infected patients with herpes zoster: Aciclovir 10 mg/kg IV 3 times daily for 10-14 days, followed by oral valacyclovir 2

Patients with Renal Impairment

Dosage adjustment required based on creatinine clearance 1:

• For 200 mg normal dose:
  • CrCl >10 mL/min: 200 mg every 4 hours
  • CrCl 0-10 mL/min: 200 mg every 12 hours
• For 800 mg normal dose:
  • CrCl >25 mL/min: 800 mg every 4 hours
  • CrCl 10-25 mL/min: 800 mg every 8 hours
  • CrCl 0-10 mL/min: 800 mg every 12 hours

Clinical Pearls and Caveats

• Aciclovir should be administered within 24 hours of symptom onset for HSV and within 72 hours for VZV for maximum efficacy 2
• Aciclovir does not eradicate latent virus or prevent subsequent recurrences 2, 3
• Oral bioavailability of aciclovir is relatively low (10-20%), requiring frequent dosing 1
• For patients unable to tolerate the frequent dosing of aciclovir, valacyclovir may be considered as it provides better bioavailability 4, 5
• Adequate hydration should be maintained during treatment to prevent crystalluria, especially with high-dose therapy 3
• Topical aciclovir is substantially less effective than oral therapy for genital herpes and is not recommended 2

Remember that early initiation of therapy is crucial for optimal clinical outcomes in both HSV and VZV infections, with treatment efficacy diminishing significantly when started beyond the recommended timeframes.