IV Acyclovir Injections: Indications and Dosing
IV acyclovir is indicated for severe, life-threatening HSV infections including encephalitis, disseminated disease, neonatal herpes, severe mucocutaneous disease in immunocompromised patients, and varicella-zoster in immunocompromised hosts—with specific weight-based dosing that must be infused over at least 1 hour to prevent renal toxicity.
Critical Administration Requirements
IV acyclovir must be infused over at least 1 hour—never as a rapid bolus—and should never be given intramuscularly, subcutaneously, or topically 1. Rapid administration causes renal tubular damage and can result in death 1.
Primary Indications and Dosing
HSV Encephalitis
- Adults/Adolescents (≥12 years): 10 mg/kg IV every 8 hours for 10 days 1
- Pediatrics (3 months-12 years): 20 mg/kg IV every 8 hours for 10 days 1
- Neonates (birth-3 months): 10 mg/kg IV every 8 hours for 10 days (some use 15-20 mg/kg, though safety/efficacy unclear) 1
For neonatal CNS disease, repeat CSF HSV DNA PCR at days 19-21 and do not stop acyclovir until negative 2.
Severe/Disseminated HSV Disease
This includes disseminated infection, pneumonitis, hepatitis, or severe disease requiring hospitalization:
- Adults/Adolescents: 5-10 mg/kg IV every 8 hours for 5-7 days until clinical resolution 3, 1
- Immunocompromised patients with severe disease: 5 mg/kg IV every 8 hours may be required 4
Mucocutaneous HSV in Immunocompromised Patients
- Adults/Adolescents: 5 mg/kg IV every 8 hours for 7 days 1
- Pediatrics (<12 years): 10 mg/kg IV every 8 hours for 7 days 1
- Moderate-to-severe gingivostomatitis: 5-10 mg/kg IV three times daily, then switch to oral when lesions regress 2
Varicella-Zoster in Immunocompromised Patients
- Adults/Adolescents: 10 mg/kg IV every 8 hours for 7 days 1
- Pediatrics (<12 years): 20 mg/kg IV every 8 hours for 7 days 1
HSV-2 Meningitis
For first episode: 10 mg/kg IV every 8 hours until resolution of fever/headache, then switch to valacyclovir 1g TID to complete 14 days 5. This is distinct from encephalitis, which requires full 14-21 day IV course 5.
Dosing Adjustments
Renal Impairment
Adjust dosing interval based on creatinine clearance 1:
- CrCl >50: Every 8 hours (standard)
- CrCl 25-50: Every 12 hours
- CrCl 10-25: Every 24 hours
- CrCl 0-10: 50% dose every 24 hours
- Hemodialysis: Administer additional dose after each dialysis 1
Obesity
Dose obese patients using ideal body weight, not actual body weight 1. Recent evidence suggests adjusted body weight for obese patients may optimize outcomes while preventing toxicity 6.
Maximum Dose
Do not exceed 20 mg/kg every 8 hours for any patient 1.
Critical Safety Considerations
Nephrotoxicity
- Renal failure (sometimes fatal) has occurred with acyclovir 1
- Ensure adequate hydration during infusion
- Monitor renal function, especially with concomitant nephrotoxic drugs
- Supra-therapeutic dosing significantly increases acute kidney injury risk (adjusted OR 12.9) 6
Other Serious Adverse Events
- TTP/HUS has resulted in death in immunocompromised patients 1
- Extravasation injuries can occur—use proper IV technique 7
- Transient creatinine elevation is common 8
When NOT to Use IV Acyclovir
Oral acyclovir is preferred for:
- First episode genital herpes in immunocompetent patients 3
- Recurrent genital herpes 3
- Mild mucocutaneous disease 2
- Herpes zoster in immunocompetent patients (oral equally effective as IV) 9
Acyclovir Resistance
Suspect resistance if lesions persist despite treatment, particularly in immunocompromised patients 4. All acyclovir-resistant strains are also resistant to valacyclovir and most to famciclovir 4. Switch to foscarnet 40 mg/kg IV every 8 hours until clinical resolution 4. Topical cidofovir 1% daily for 5 days is an alternative 4.
Preparation and Administration
- Reconstitute 500 mg vial with 10 mL sterile water (1000 mg with 20 mL) to achieve 50 mg/mL 1
- Further dilute to ≤7 mg/mL in appropriate IV solution 1
- Do NOT use bacteriostatic water containing benzyl alcohol or parabens 1
- Use reconstituted solution within 12 hours; diluted solution within 24 hours 1
Special Populations
Pregnancy
While safety not fully established, IV acyclovir is indicated for life-threatening maternal HSV (disseminated infection, encephalitis, pneumonitis, hepatitis) 4. Registry data show no increased birth defects 4.
HIV/Immunocompromised
May require higher doses (e.g., 400 mg PO 3-5 times daily for oral therapy) and longer duration 4. For severe cases, 5 mg/kg IV every 8 hours 4.