Is acyclovir 750mg thrice daily an appropriate dose for a 75kg adult?

Acyclovir 750mg Three Times Daily is NOT an Appropriate Dose for a 75kg Adult

The correct dose of intravenous acyclovir for a 75kg adult is 750mg (10 mg/kg) three times daily for most viral encephalitis indications, making this dosing regimen appropriate. 1

Standard Dosing for Viral Encephalitis

HSV and VZV Encephalitis

• For HSV encephalitis, the standard dose is 10 mg/kg three times daily intravenously, which equals 750mg per dose for a 75kg patient 1
• For VZV encephalitis, guidelines recommend 10-15 mg/kg three times daily, with 10 mg/kg being the most commonly used dose due to renal safety concerns 1
• The higher dose of 15 mg/kg (1,125mg per dose for 75kg patient) is suggested only if renal function is normal and requires frequent renal function monitoring 1

Critical Safety Considerations

Renal Function Monitoring

• Acyclovir must be renally dosed and carefully monitored in patients with limited kidney function to prevent serious neurological side effects 2
• The most important adverse effect is crystalluria and elevated serum creatinine related to bolus intravenous administration 3
• Dosage adjustment is required in patients with renal failure, as the drug is excreted primarily by glomerular filtration and tubular secretion 3, 4

Nephrotoxicity Prevention

• Acyclovir has potential to cause obstructive nephropathy, particularly with rapid bolus administration 4
• Ensure adequate hydration and avoid rapid bolus infusion to minimize crystalluria risk 3
• Monitor serum creatinine frequently during therapy, especially in elderly patients or those with baseline renal impairment 2

Administration Guidelines

Infusion Considerations

• Acyclovir should be administered as a slow intravenous infusion, not as a rapid bolus 3
• The drug distributes into most body tissues, including vesicular fluid and the central nervous system 5
• Peak plasma concentrations occur 1.5 to 2.5 hours after administration with oral dosing, but IV administration provides more reliable levels 5

Duration of Therapy

• For VZV encephalitis, treatment duration is typically up to 14 days, especially if started within a few days of symptom onset 1
• Immunocompromised patients with VZV encephalitis may require prolonged courses of intravenous acyclovir 1

Common Pitfalls to Avoid

Dosing Errors in Special Populations

• In patients over 65 years, renal function declines with age and dosing must be adjusted accordingly 2
• Failure to adjust for renal function in patients on hemodialysis can lead to serious neurological sequelae including confusion and ataxia 2
• For patients with creatinine clearance <50 mL/min, dose reduction is mandatory 3

Monitoring Neurological Status

• Be alert for altered mental status, confusion, or ataxia as signs of acyclovir toxicity, particularly in patients with renal impairment 2
• These neurological symptoms can develop progressively over days and require prompt recognition and dialysis if severe 2

Weight-Based Dosing Verification

• Always calculate the exact mg/kg dose rather than using fixed dosing 1
• For a 75kg patient: 10 mg/kg × 75kg = 750mg per dose, three times daily 1
• Verify that the total daily dose (2,250mg for this patient) is appropriate for the indication and renal function 1