What is the recommended dosing of acyclovir (antiviral medication) for viral pneumonia?

Acyclovir Dosing for Viral Pneumonia

Acyclovir is indicated specifically for varicella-zoster virus (VZV) and herpes simplex virus (HSV) pneumonia, not for typical viral pneumonias caused by influenza, RSV, or other common respiratory viruses.

Recommended Dosing Regimens

VZV Pneumonia (Varicella/Chickenpox Pneumonia)

• Intravenous acyclovir 10 mg/kg every 8 hours (three times daily) is the standard dose 1
• Higher doses of 15 mg/kg every 8 hours may be considered if renal function is normal, though most clinicians use the 10 mg/kg dose due to renal safety concerns 1
• Treatment duration: typically 7-14 days, depending on clinical response 1
• Early initiation is critical - therapy should be started as soon as varicella pneumonia is suspected, as delay worsens outcomes 2

HSV Pneumonia

• Parenteral acyclovir is recommended at standard antiviral doses 1
• The dosing parallels HSV encephalitis treatment: 10 mg/kg intravenously every 8 hours 1
• Treatment duration: 14-21 days 1

Critical Clinical Considerations

Renal Function Monitoring

• Dose adjustment is mandatory in renal impairment - acyclovir is eliminated primarily by the kidneys via glomerular filtration and tubular secretion 3
• Monitor renal function frequently, especially at higher doses (15 mg/kg) 1
• The most important adverse effect is crystalluria and elevated serum creatinine related to bolus intravenous administration 3
• Administer as slow infusion over 1 hour, never as bolus, to prevent crystalluria 3

Patient Populations Requiring Special Attention

Immunocompromised Patients:

• May require prolonged courses of intravenous acyclovir 1
• Higher doses (up to 43.2 mg/kg/day by continuous infusion) have been studied in immunocompromised patients with herpesvirus infections 4
• Standard dosing remains 10 mg/kg every 8 hours, but treatment duration may need extension 1

Pediatric Patients:

• Body weight and estimated creatinine clearance significantly affect acyclovir pharmacokinetics 5
• Children with low body weight (≤10 kg) and high creatinine clearance (≥5.5 liters/h/m²) may require higher doses than standard weight-based dosing 5

Important Limitations and Pitfalls

Acyclovir is NOT Effective For:

• Influenza pneumonia - use oseltamivir, zanamivir, or amantadine/rimantadine instead 1
• RSV pneumonia - no established antiviral therapy for adults 1
• Parainfluenza, adenovirus, metapneumovirus, or SARS - no effective antiviral agents 1
• Cytomegalovirus (CMV) pneumonia - requires ganciclovir or foscarnet, not acyclovir 1

Bacterial Superinfection

• Superinfection with bacteria is common in adults with viral pneumonia 6
• If bacterial superinfection is suspected (particularly with influenza), empiric antibacterial therapy targeting S. pneumoniae, S. aureus, and H. influenzae should be added 1
• Consider amoxicillin-clavulanate, cefpodoxime, cefuroxime, or a respiratory fluoroquinolone 1

Administration Technique

• Administer by slow intravenous infusion over at least 1 hour 3
• Ensure adequate hydration to prevent crystalluria 3
• Monitor for infusion site inflammation 3

Key Point on Viral Identification

The provided guidelines focus primarily on encephalitis rather than pneumonia 1. However, the principles for VZV and HSV treatment with acyclovir remain consistent across organ systems, with parenteral acyclovir 10 mg/kg every 8 hours being the cornerstone of therapy 1, 2.