What volume of clarithromycin suspension (250 mg/5 ml) should be administered to a 9‑year‑old child weighing 37 kg?

Clarithromycin Dosing Calculation for a 9-Year-Old Child Weighing 37 kg

For a 37 kg, 9-year-old child, administer 11 mL of clarithromycin 250 mg/5 mL suspension twice daily.

Step-by-Step Dosing Calculation

Standard Pediatric Dose

• The CDC recommends clarithromycin at 15 mg/kg/day divided into 2 doses for children over 1 month of age, with a maximum daily dose of 1 g. 1

Weight-Based Calculation for This Patient

• Total daily dose: 37 kg × 15 mg/kg = 555 mg/day 2
• Dose per administration: 555 mg ÷ 2 = 277.5 mg per dose (twice daily) 2
• This is well below the 1 g/day maximum, so no dose adjustment is needed. 1

Volume Calculation Using Available Suspension

• Suspension concentration: 250 mg per 5 mL 2
• Volume per dose: (277.5 mg ÷ 250 mg) × 5 mL = 5.55 mL per dose 2
• Practical rounding: Round to 5.5 mL per dose for ease of measurement 2

Alternative Weight-Based Dosing Reference

• The British Thoracic Society provides weight-band dosing: for children 30–40 kg, the recommended dose is 250 mg twice daily, which equals 5 mL of the 250 mg/5 mL suspension twice daily. 1, 2
• This weight-band approach yields 5 mL twice daily, which is very close to the calculated 5.5 mL and represents a practical, guideline-supported alternative. 1, 2

Final Dosing Recommendation

Administer either:

• 5.5 mL twice daily (precise weight-based calculation) 1, 2, OR
• 5 mL twice daily (British Thoracic Society weight-band dosing for 30–40 kg children) 1, 2

Both approaches are clinically appropriate; the 5 mL dose offers simpler measurement while the 5.5 mL dose provides slightly higher precision for this 37 kg child. 1, 2

Treatment Duration and Administration

• Standard duration: 7 days for most respiratory infections including pertussis 1, 2
• Administration: Can be given with or without food; administering with food may improve gastrointestinal tolerability 3, 4
• Timing: Administer every 12 hours (twice daily) 1, 2

Critical Safety Considerations

Absolute Contraindications

• Macrolide hypersensitivity: Do not administer if the child has a history of allergic reaction to any macrolide antibiotic (clarithromycin, azithromycin, erythromycin). 1, 2
• Drug interactions: Avoid concomitant use with astemizole, cisapride, pimozide, or terfenadine due to risk of serious cardiac arrhythmias. 1

Common Adverse Effects

• Gastrointestinal effects (2–6% of patients): epigastric distress, abdominal cramps, nausea, vomiting, diarrhea 1, 2
• These are typically mild to moderate and rarely require discontinuation. 3

Rare but Serious Reactions

• QTc prolongation, hepatotoxicity, Stevens-Johnson syndrome, and anaphylaxis can occur but are rare. 2
• Baseline ECG is recommended before starting therapy if risk factors for QT prolongation exist. 2

Drug Interaction Warnings

• CYP3A inhibition: Clarithromycin inhibits the cytochrome P450 3A enzyme system, potentially increasing concentrations of drugs metabolized by this pathway (e.g., carbamazepine, cyclosporine, digoxin, theophylline, warfarin, certain benzodiazepines). 1, 4
• Review all concurrent medications before prescribing clarithromycin. 1

Dosage Adjustments

• Renal impairment: Dosage adjustment required in severe renal impairment (creatinine clearance < 1.8 L/h or < 30 mL/min). 2, 4
• Hepatic impairment: No adjustment needed for isolated hepatic impairment with normal renal function. 1, 2

Clinical Monitoring

• Expected response: Clinical improvement should occur within 48–72 hours of starting therapy. 1
• Treatment failure: If no improvement or worsening occurs after 48–72 hours, reassess the diagnosis and consider alternative pathogens or complications. 1
• Complete the course: Ensure the full 7-day course is completed even if symptoms resolve earlier to prevent resistance and recurrence. 1, 2