What is the typical dosage of amoxicillin (amoxicillin) for adults and pediatric patients?

Amoxicillin Dosing for Adults and Pediatric Patients

For pediatric patients with respiratory infections, amoxicillin should be dosed at 45 mg/kg/day divided every 12 hours for mild-to-moderate infections, or 90 mg/kg/day divided every 12 hours for severe infections or areas with high pneumococcal resistance, with a maximum daily dose of 4000 mg. 1, 2 For adults with sinusitis, the standard dose is 500 mg twice daily for uncomplicated cases. 3

Pediatric Dosing

Standard Respiratory Infections

• Mild-to-moderate infections: 45 mg/kg/day divided every 12 hours 3, 1, 2
• Severe infections or high resistance areas: 90 mg/kg/day divided every 12 hours 3, 1, 2
• Maximum daily dose: 4000 mg (4 g) per day regardless of weight 1, 4

Group A Streptococcal Infections (Including Scarlet Fever)

• Dose: 50-75 mg/kg/day divided into 2 doses for 10 days 1, 4
• Maximum per dose: 1000 mg 1, 4
• Patients become non-contagious after 24 hours of therapy 1, 4

Age-Specific Considerations

• Neonates and infants ≤3 months: Maximum 30 mg/kg/day divided every 12 hours 5
• Children <40 kg: Weight-based dosing as above 1
• Children ≥40 kg: Use adult dosing 1

Treatment Duration

• Most respiratory infections: 7-10 days 1, 4
• Pneumonia specifically: 10 days 1, 2, 4
• Group A Streptococcal infections: 10 days mandatory to prevent rheumatic fever 1, 4

Adult Dosing

Sinusitis and Upper Respiratory Infections

• Standard dose: 500 mg twice daily 3
• Alternative: 875 mg twice daily for more severe infections 6
• Duration: 10-14 days, or continue for 7 days after symptom resolution 3

Treatment Failure Protocol

• If no improvement after 3-5 days, switch to high-dose amoxicillin-clavulanate (875 mg/125 mg twice daily) or cefuroxime 3
• Resistance is common: 25-50% of S. pneumoniae show penicillin resistance, and nearly 50% of H. influenzae produce β-lactamase 3

Helicobacter pylori (Adults Only)

• Triple therapy: 1000 mg amoxicillin + 500 mg clarithromycin + 30 mg lansoprazole, all twice daily for 14 days 5
• Dual therapy: 1000 mg amoxicillin + 30 mg lansoprazole, all three times daily for 14 days 5

Amoxicillin-Clavulanate (Augmentin) Dosing

Pediatric High-Dose Formulation

• Dose: 90 mg/kg/day of amoxicillin component with 6.4 mg/kg/day clavulanate, divided every 12 hours 3, 4
• Maximum: Not to exceed 2000 mg amoxicillin every 12 hours 3
• This formulation provides better coverage for penicillin-resistant S. pneumoniae (MIC ≤2 mg/L) 7

Standard Pediatric Formulation

• Dose: 45 mg/kg/day of amoxicillin component divided every 12 hours or 40 mg/kg/day divided every 8 hours 3, 4

Adult Formulation

• Standard: 500-875 mg amoxicillin with 125 mg clavulanate twice daily 3, 6
• Twice-daily dosing (875/125 mg) is as effective as three-times-daily dosing (500/125 mg) with similar adverse event profiles 6

Renal Impairment Adjustments

• GFR 10-30 mL/min: 500 mg or 250 mg every 12 hours 1
• GFR <10 mL/min: 500 mg or 250 mg every 24 hours 1

Critical Monitoring Parameters

Expected Clinical Response

• Clinical improvement should occur within 48-72 hours of starting treatment 1, 2, 4
• If no improvement by 72 hours, reassess diagnosis and consider alternative antibiotics 1, 2

Adverse Effects

• Most common: Diarrhea, nausea, vomiting, and rash (>1% incidence) 5
• Severe diarrhea: Occurs in approximately 7% of patients regardless of dose 8
• Twice-daily dosing reduces diarrhea frequency compared to three-times-daily regimens 7

Important Clinical Pitfalls

Dosing Errors to Avoid

• Never underdose in high-resistance areas: Use 90 mg/kg/day for severe infections or known resistance 1, 2
• Complete the full course: Even if symptoms improve, finish the prescribed duration to prevent relapse and resistance 3, 1
• Twice-daily dosing improves adherence: The 45-90 mg/kg/day divided every 12 hours is preferred over more frequent dosing 1, 9

When Amoxicillin Alone Is Insufficient

• If β-lactamase-producing H. influenzae or M. catarrhalis is suspected, use amoxicillin-clavulanate instead 3
• If MRSA is suspected or confirmed, amoxicillin will not be effective and alternative antibiotics must be used 1, 2
• In regions with high antibiotic resistance, consider starting with high-dose amoxicillin-clavulanate rather than amoxicillin alone 3

Prescription Clarity

• Every prescription should specify: total daily dose in mg/kg/day, number of divided doses, duration of therapy, and indication 1
• For a 13.6 kg child with pneumonia: prescribe "amoxicillin 250 mg/5 mL suspension, give 6.1 mL twice daily for 10 days" (45 mg/kg/day) 4