What volume of a 200 mg/5 mL acyclovir oral suspension should be given to a 16‑kg child with normal renal function for the standard pediatric dose of 20 mg/kg every 8 hours?

Acyclovir Oral Suspension Volume Calculation for a 16-kg Child

For a 16-kg child with normal renal function receiving the standard pediatric dose of 20 mg/kg every 8 hours, administer 8 mL of the 200 mg/5 mL acyclovir oral suspension per dose.

Dose Calculation

• Required dose per administration: 20 mg/kg × 16 kg = 320 mg 1
• Suspension concentration: 200 mg per 5 mL = 40 mg/mL 1
• Volume calculation: 320 mg ÷ 40 mg/mL = 8 mL per dose 1

Dosing Schedule and Duration

• Frequency: Administer every 8 hours (three times daily) 1, 2
• Duration: Continue for 7–10 days or until no new lesions appear for 48 hours, depending on the specific indication 1, 3
• Timing of initiation: Start therapy within 72 hours of symptom onset for maximal clinical benefit 1, 3

Administration Instructions

• Shake the oral suspension well before each dose to ensure uniform drug concentration 1
• May be administered with or without food; giving with meals may improve gastrointestinal tolerability 4, 3
• The commercially available suspension provides a final concentration of 6 mg/mL when reconstituted according to package instructions; however, your preparation is 200 mg/5 mL (40 mg/mL), which is a different concentration 4

Critical Monitoring Parameters

• Hydration: Ensure adequate fluid intake throughout treatment to prevent acyclovir crystalluria and renal toxicity 2, 3
• Clinical response: Expect improvement within 48–72 hours of initiating therapy 2
• Renal function: This dose assumes normal renal function; dose reduction is required if creatinine clearance is impaired 4, 1

Common Pitfalls to Avoid

• Do not underdose: Always calculate based on actual body weight (20 mg/kg), not a fixed adult dose 1
• Do not exceed maximum single dose: The maximum single oral dose is 800 mg; this 16-kg child's 320-mg dose is well within safe limits 1
• Do not use topical formulations: Topical acyclovir is substantially less effective than oral therapy for systemic infections and should be avoided 2, 3
• Do not discontinue early: Continue the full course even if symptoms improve; stop only when all lesions have fully resolved or the prescribed duration is complete 3

Escalation to Intravenous Therapy

• Switch to intravenous acyclovir 10 mg/kg every 8 hours if the child develops severe disease, disseminated infection, or complications requiring hospitalization 1, 2, 3
• For children with severe immunosuppression (CDC category 3), IV therapy is preferred from the outset 1, 2