What is the recommended dose of co-amoxiclav (amoxicillin/clavulanic acid) for a 9-year-old child weighing 35 kg with a suspected bacterial infection and no known allergies to penicillin?

Co-Amoxiclav Dosing for a 9-Year-Old Child (35 kg)

For a 9-year-old child weighing 35 kg with a suspected bacterial infection, the recommended dose of co-amoxiclav is 90 mg/kg/day of the amoxicillin component divided into 2 doses (1575 mg twice daily), which translates to approximately 16 mL of the 600 mg/5 mL suspension twice daily, for a duration of 7-10 days depending on the specific infection. 1, 2

Weight-Based Calculation

• For this 35 kg child, the high-dose regimen provides: 35 kg × 90 mg/kg/day = 3150 mg/day total, or 1575 mg per dose twice daily 1, 2
• This dose should not exceed the maximum daily limit of 4000 mg/day of amoxicillin, which this child is well below 1, 3
• The high-dose formulation maintains a 14:1 ratio of amoxicillin to clavulanate (90 mg/kg amoxicillin with 6.4 mg/kg clavulanate), which minimizes gastrointestinal side effects while maintaining efficacy 2, 4

Rationale for High-Dose Regimen

The 90 mg/kg/day dosing is strongly preferred over lower doses (45 mg/kg/day) for most bacterial infections in children because it provides adequate coverage against penicillin-resistant Streptococcus pneumoniae and β-lactamase-producing organisms like Haemophilus influenzae and Moraxella catarrhalis. 1, 2

• High-dose therapy achieves tissue concentrations that exceed the minimum inhibitory concentration for intermediately resistant S. pneumoniae and many highly resistant serotypes 2
• The 90 mg/kg/day regimen eradicated penicillin-resistant S. pneumoniae with MICs of 2-4 mg/L in clinical trials, with clinical response rates of 76-95% 2, 5
• Using standard lower doses when high-dose therapy is indicated leads to treatment failure with resistant organisms 2

Indication-Specific Considerations

For Community-Acquired Pneumonia:

• Use 90 mg/kg/day in 2 doses for 10 days 1, 2, 3
• This applies to both children under and over 5 years of age 3
• Clinical improvement should occur within 48-72 hours; if no improvement by 72 hours, reassess the diagnosis and consider atypical pathogens 1, 2

For Acute Otitis Media or Sinusitis:

• Use 90 mg/kg/day in 2 doses for 10 days 2
• High-dose regimen is particularly indicated if the child has recent antibiotic exposure (within 30 days), daycare attendance, or age <2 years 2

For Group A Streptococcal Infections:

• A dose of 50-75 mg/kg/day in 2 doses for 10 days is adequate, not exceeding 1000 mg per dose 1, 3
• The full 10-day course is essential to prevent rheumatic fever 3

Practical Dosing Algorithm

For age-based dosing (when weight is unavailable):

• Children 7-12 years: 5 mL of 250/62 suspension three times daily for standard infections 2
• However, weight-based dosing is strongly preferred and more accurate than age-based dosing 1

For this specific 35 kg child:

• Using the high-dose 600 mg/5 mL suspension: approximately 16 mL twice daily 1, 2
• Alternatively, using 250/62 suspension: approximately 32 mL twice daily (though this is a large volume and the higher concentration suspension is preferred) 2

Treatment Duration and Monitoring

• Standard duration is 7-10 days for most respiratory and soft tissue infections 2
• Pneumonia specifically requires 10 days of treatment 1, 2, 3
• Children should demonstrate clinical improvement within 48-72 hours of starting therapy 1, 2
• If no improvement or worsening occurs after 72 hours, reevaluation is necessary, including consideration of atypical pathogens, complications, or alternative diagnoses 1, 2

Critical Pitfalls to Avoid

Underdosing is a common and dangerous error:

• Using 40-45 mg/kg/day when 90 mg/kg/day is indicated fails to achieve adequate tissue concentrations and promotes antimicrobial resistance 1, 3
• Subtherapeutic doses cannot overcome even susceptible organisms and increase the risk of treatment failure 2

Verify suspension concentration before dispensing:

• The 125/31,250/62, and 600 mg/5 mL formulations require different volumes for the same dose 2
• Confusion between formulations is a common source of dosing errors 2

Consider renal function:

• In children with renal insufficiency, prolonging the dosing interval according to creatinine clearance is essential to avoid accumulation 2

Adverse Effects

• The most common adverse effects are gastrointestinal disturbances, including diarrhea (25% vs 15% placebo), nausea, and vomiting 1, 2
• The 14:1 ratio high-dose formulation causes less diarrhea than other amoxicillin-clavulanate preparations while maintaining efficacy 2
• Rash, urticaria, and hypersensitivity reactions may occur 1
• Serious but rare adverse effects include anaphylaxis, Stevens-Johnson syndrome, and toxic epidermal necrolysis 3

Evidence Quality Note

Recent high-quality randomized controlled trials (CAP-IT trial, 2021) demonstrated that lower doses (35-50 mg/kg/day) were noninferior to higher doses (70-90 mg/kg/day) for community-acquired pneumonia in children discharged from emergency departments 6, 7. However, these findings apply specifically to children with uncomplicated CAP who have already received initial treatment and are being discharged. For initial empiric therapy, particularly when resistant organisms are suspected or the child has risk factors (age <2 years, daycare attendance, recent antibiotics), the high-dose regimen remains the standard of care per multiple guideline organizations 1, 2, 3.