How do I write an order for Zovirax (Acyclovir)?

How to Write an Order for Zovirax (Acyclovir)

The specific order for Zovirax depends on the indication, route of administration, and patient's renal function, with oral dosing ranging from 200-800 mg per dose and IV dosing from 5-12.4 mg/kg every 8 hours, adjusted for creatinine clearance. 1

Oral Dosing by Indication

Herpes Zoster (Shingles)

• Order: Acyclovir 800 mg PO five times daily for 7-10 days 1
• Initiate at earliest sign of rash for maximum benefit 2
• This high-dose regimen (800 mg vs 400 mg) significantly reduces viral shedding, accelerates healing, and decreases acute pain severity 2

Genital Herpes

• Initial episode: Acyclovir 200 mg PO every 4 hours (5 times daily) for 10 days 1
• Recurrent episodes: Acyclovir 200 mg PO every 4 hours (5 times daily) for 5 days 1
• Chronic suppression: Acyclovir 400 mg PO twice daily for up to 12 months 1
• Alternative suppressive regimens include 200 mg three times daily to 200 mg five times daily 1

Chickenpox (Varicella)

• Children ≥2 years: Acyclovir 20 mg/kg PO four times daily (maximum 800 mg/dose) for 5 days 1
• Adults and children >40 kg: Acyclovir 800 mg PO four times daily for 5 days 1
• Initiate within 24 hours of rash onset for efficacy 1

Herpes Simplex Virus (HSV) Infections

• Superficial HSV-1 or HSV-2: Acyclovir 200-400 mg PO three times daily until lesions resolve 3
• For frequent recurrences, consider prophylactic dosing 3

Intravenous Dosing

Standard IV Dosing

• Order: Acyclovir 5-12.4 mg/kg IV every 8 hours 3
• Infuse over at least 30 minutes to prevent crystalluria 3
• Ensure adequate hydration with IV saline or 5% dextrose before and during infusion 3

Systemic HSV or Severe Infections

• Acyclovir 10 mg/kg IV every 8 hours for CNS or disseminated disease 4
• Continue IV therapy until clinical response, then switch to oral therapy to complete 14-21 days total 3
• Consider temporary reduction in immunosuppression for transplant recipients 3

Renal Dose Adjustments

Critical: Always adjust dosing based on creatinine clearance to prevent nephrotoxicity 3, 1

For 200 mg Every 4 Hours Regimen

• CrCl >10 mL/min: 200 mg every 4 hours (5 times daily) 1
• CrCl <10 mL/min: 200 mg every 12 hours 1, 3

For 400 mg Every 12 Hours Regimen

• CrCl >10 mL/min: 400 mg every 12 hours 1
• CrCl 0-10 mL/min: 200 mg every 12 hours 1

For 800 mg Every 4 Hours Regimen

• CrCl >25 mL/min: 800 mg every 4 hours (5 times daily) 1
• CrCl 10-25 mL/min: 800 mg every 8 hours 1
• CrCl <10 mL/min: 800 mg every 12 hours 1

For IV Dosing with Renal Impairment

• CrCl 10-50 mL/min: 5-12.4 mg/kg every 12-24 hours 3
• CrCl <10 mL/min: 2.5-5 mg/kg every 24 hours 3

Hemodialysis Patients

• Administer additional dose after each dialysis session 3, 1
• Hemodialysis removes approximately 60% of plasma acyclovir over 6 hours 1

Critical Safety Considerations

Nephrotoxicity Prevention

• High-dose acyclovir has known nephrotoxic potential and requires close supervision 3
• Crystalluria occurs with bolus IV administration; prevent by ensuring adequate hydration 5
• Monitor serum creatinine within 48 hours before each dose in high-risk patients 3

Common Pitfalls to Avoid

• Never administer IV acyclovir as a bolus—infuse over at least 30 minutes 3
• Do not initiate therapy >24 hours after chickenpox onset; efficacy is not established 1
• Acyclovir does not eradicate latent virus or prevent future recurrences 5, 6
• Re-evaluate suppressive therapy after 12 months to assess ongoing need 1

Drug Interactions

• Monitor closely when used with other nephrotoxic agents (amphotericin B, cidofovir, foscarnet, pentamidine) 3
• Probenecid may decrease renal clearance of acyclovir 3

Special Populations

Immunocompromised Patients

• Consider body surface area dosing: 500 mg/m²/dose IV every 8 hours for children >1 year 4
• May require longer treatment duration and temporary reduction in immunosuppression 3

Pregnancy

• Use when benefits clearly outweigh risks 7
• Intravenous acyclovir has shown benefit in severe HSV complications during pregnancy 6