What is the appropriate dose of co‑amoxiclav suspension (125 mg/31.25 mg per 5 ml) for a pediatric patient weighing 18 kg?

Co-Amoxiclav Dosing for an 18 kg Pediatric Patient

For an 18 kg child, prescribe 7.5 mL of co-amoxiclav 125/31.25 mg per 5 mL suspension twice daily for 10 days, providing 90 mg/kg/day of the amoxicillin component. 1, 2

Weight-Based High-Dose Regimen (Preferred)

The current standard of care for most pediatric infections is high-dose amoxicillin-clavulanate at 90 mg/kg/day divided into two doses, which for an 18 kg child equals 1,620 mg total daily amoxicillin (810 mg per dose). 1, 2, 3

Practical Dosing Calculation

• Using the 125/31.25 mg per 5 mL suspension: Each 5 mL contains 125 mg amoxicillin, so 810 mg per dose requires approximately 32.4 mL per dose (810 ÷ 125 × 5 = 32.4 mL). 4
• This suspension strength is NOT optimal for high-dose therapy in this weight range—the volume is impractically large. 2, 4

Recommended Alternative Formulation

• Switch to the 200 mg/5 mL or 250 mg/5 mL suspension to deliver the high-dose regimen in a reasonable volume. 1, 2
• Using a 200 mg/5 mL suspension: 810 mg per dose = 20.25 mL twice daily. 1
• Using a 250 mg/5 mL suspension: 810 mg per dose = 16.2 mL twice daily. 1

Age-Based Dosing (Lower Dose—Use Only for Mild Infections Without Risk Factors)

If you must use the 125/31.25 mg per 5 mL suspension and the child has no risk factors for resistant organisms, the age-based guideline dosing is:

• For children 1–6 years: 5 mL of 125/31 suspension three times daily. 5, 3
• This provides only 375 mg/day total amoxicillin (approximately 21 mg/kg/day for an 18 kg child), which is substantially below the recommended 45–90 mg/kg/day for most infections. 1, 3

This low-dose regimen is outdated and should be avoided for any infection requiring antibiotic therapy, as it fails to achieve adequate serum and tissue concentrations to overcome even susceptible organisms and promotes antimicrobial resistance. 1, 3

Indications for High-Dose Therapy (90 mg/kg/day)

Use the high-dose regimen (90 mg/kg/day in two divided doses) if the child has ANY of the following risk factors:

• Age < 2 years 1, 2, 3
• Attendance at daycare 1, 2, 3
• Antibiotic use within the past 30 days 1, 2, 3
• Incomplete Hib vaccination (< 3 doses) 2, 3
• Residence in an area where > 10% of S. pneumoniae are penicillin-resistant 1, 2, 3
• Moderate to severe illness at presentation 1, 2, 3
• Concurrent purulent acute otitis media 2, 3
• Prior treatment failure with amoxicillin alone 2, 3

Infection-Specific Dosing

Community-Acquired Pneumonia

• Children < 5 years: 90 mg/kg/day in two divided doses for 10 days. 1, 2, 3
• Children ≥ 5 years: 90 mg/kg/day in two divided doses (maximum 4 g/day) for 10 days. 1, 2, 3

Acute Otitis Media

• 90 mg/kg/day in two divided doses for 10 days, especially for children < 2 years or with risk factors. 1, 2, 3

Acute Bacterial Rhinosinusitis

• 90 mg/kg/day in two divided doses for 10–14 days as first-line therapy. 2, 3

Skin and Soft-Tissue Infections

• For children < 1 year: 0.266 mL/kg of 125/31 suspension three times daily. 2
• Duration: 7–10 days, extendable to 14 days based on clinical response. 2

Treatment Duration and Monitoring

• Standard duration: 10 days for most pediatric respiratory infections. 1, 2, 3
• Clinical improvement should occur within 48–72 hours of starting therapy. 1, 2, 3
• If no improvement or worsening after 48–72 hours: Re-evaluate diagnosis, consider atypical pathogens (add a macrolide), assess for complications, or switch antibiotics. 1, 2, 3
• Continue therapy for at least 48–72 hours after complete resolution of symptoms to reduce relapse risk. 1

Critical Dosing Pitfalls to Avoid

• Do NOT use age-based dosing when high-dose therapy is indicated—this leads to treatment failure against resistant organisms. 2, 3
• Verify the suspension concentration (125/31 vs. 250/62 mg per 5 mL) before calculating volume to avoid dosing errors. 2, 3
• The 125/31.25 mg per 5 mL suspension is NOT interchangeable with other co-amoxiclav formulations due to differing clavulanate ratios. 4
• Do NOT prescribe antibiotics for viral upper respiratory tract infections—most URTIs are viral and do not benefit from antibiotics. 3

Maximum Dosing Limits

• Maximum single dose: 2,000 mg amoxicillin per administration, regardless of weight. 1, 2, 3
• Maximum daily dose: 4,000 mg amoxicillin per day. 1, 2

Alternatives for Penicillin Allergy

• Non-anaphylactic reactions: Second- or third-generation cephalosporins (cefdinir, cefuroxime, cephalexin). 1, 2, 3
• Type I (IgE-mediated) reactions: Clindamycin (10–20 mg/kg/day in three doses) or azithromycin (12 mg/kg once daily for 5 days), acknowledging inferior efficacy compared to β-lactams. 1, 2, 3

Administration Guidance

• Administer at the start of a meal to minimize gastrointestinal intolerance and enhance clavulanate absorption. 4
• Shake the suspension well before each use. 4
• Refrigerate after reconstitution and use within 10 days. 4