What is the recommended dosage and liquid formulation of amoxicillin (amoxicillin) for a patient weighing 91 pounds?

Amoxicillin Dosing for a 91-Pound Patient

For a patient weighing 91 pounds (41.4 kg), the recommended amoxicillin dosage depends on the infection type and severity, but for most common infections, use 45 mg/kg/day divided into two doses (approximately 930 mg twice daily) for mild-to-moderate infections, or 80-90 mg/kg/day divided into two doses (approximately 1650-1860 mg twice daily) for severe infections or when resistant organisms are suspected. 1

Weight Conversion and Dosing Calculations

• 91 pounds = 41.4 kg 1

Standard Dosing by Infection Severity

Mild to Moderate Infections

• Standard dose: 25 mg/kg/day divided every 12 hours (approximately 520 mg twice daily) 1
• Alternative: 20 mg/kg/day divided every 8 hours (approximately 275 mg three times daily) 1
• This applies to ear/nose/throat infections, skin/skin structure infections, and genitourinary tract infections in patients without risk factors for resistant organisms 1

Moderate to Severe Infections

• High dose: 45 mg/kg/day divided every 12 hours (approximately 930 mg twice daily) 1
• Alternative: 40 mg/kg/day divided every 8 hours (approximately 550 mg three times daily) 1
• This applies to lower respiratory tract infections and severe infections of other sites 1

High-Risk or Resistant Organism Situations

• Very high dose: 80-90 mg/kg/day divided every 12 hours (approximately 1650-1860 mg twice daily) 2
• Use this dosing for patients with recent antibiotic exposure (within 30 days), daycare attendance, age <2 years, or in communities with high rates of resistant *Streptococcus pneumoniae* (>10%) 2
• For acute bacterial sinusitis in high-risk patients, amoxicillin-clavulanate at 90 mg/kg/day of the amoxicillin component is recommended 2

Liquid Formulation Selection

Available Oral Suspension Strengths

• 125 mg/5 mL suspension 1
• 250 mg/5 mL suspension 1

Practical Dosing Examples

For standard dosing (45 mg/kg/day = 930 mg twice daily):

• Using 250 mg/5 mL suspension: Give 18.6 mL (approximately 19 mL) twice daily 1

For high-dose therapy (90 mg/kg/day = 1860 mg twice daily):

• Using 250 mg/5 mL suspension: Give 37.2 mL (approximately 37 mL) twice daily 1
• This volume may be impractical; consider tablets if the patient can swallow them 1

Important Clinical Considerations

Duration of Therapy

• Minimum treatment duration: 48-72 hours beyond symptom resolution 1
• For Streptococcus pyogenes infections: Minimum 10 days to prevent acute rheumatic fever 1
• For acute bacterial sinusitis: 10-14 days 2

Administration Instructions

• Take at the start of meals to minimize gastrointestinal intolerance 1
• Shake oral suspension well before each use 1
• Refrigeration is preferable but not required 1
• Discard unused suspension after 14 days 1

Common Pitfalls to Avoid

• Do not underdose in high-risk patients: Recent antibiotic use, daycare exposure, and age <2 years are critical risk factors requiring higher doses 2
• Do not use 875 mg tablets in renal impairment: If GFR <30 mL/min, this dose is contraindicated 1
• Do not assume standard dosing is adequate for resistant organisms: In areas with >10% penicillin-resistant S. pneumoniae, high-dose therapy should be initiated 2
• Twice-daily dosing improves compliance compared to three-times-daily regimens without compromising efficacy 3

When to Consider Amoxicillin-Clavulanate Instead

• Recent antibiotic use within 4-6 weeks 2
• Moderate to severe illness 2
• Age younger than 2 years 2
• Suspected β-lactamase-producing organisms (H. influenzae, M. catarrhalis) 2
• Use amoxicillin-clavulanate 90/6.4 mg/kg/day (of amoxicillin component) in two divided doses for these situations 2