Amoxicillin: Indications, Dosing, and Precautions
Primary Indications
Amoxicillin is the first-line antibiotic for most common bacterial infections in both adults and children due to its narrow spectrum, excellent safety profile, and low cost. 1, 2
Respiratory Tract Infections
- Group A Streptococcal Pharyngitis: Amoxicillin 50 mg/kg once daily (maximum 1000 mg) for 10 days in children, or 500 mg twice daily for 10 days in adults 1, 2
- Acute Bacterial Rhinosinusitis: High-dose amoxicillin-clavulanate (90 mg/kg/day of amoxicillin component in children; 4 g/day in adults) is preferred over amoxicillin alone due to β-lactamase-producing organisms 3, 4
- Community-Acquired Pneumonia: Amoxicillin is the preferred first-line agent for mild-to-moderate CAP in children and adults 5
Other Infections
- Acute Otitis Media: Amoxicillin remains first-line therapy 3
- Lyme Disease: 500 mg three times daily in adults; 50 mg/kg/day in 3 divided doses (maximum 500 mg per dose) in children for 10 days 9
- Skin and Soft Tissue Infections: Effective for streptococcal infections 7
- Urinary Tract Infections: Single-dose therapy (3 g in adults, 100 mg/kg in children) can be effective for uncomplicated UTI 10
Specialized Indications
- Endocarditis Prophylaxis: 2 g orally 1 hour before dental/oral procedures in adults; 50 mg/kg in children 11
- Helicobacter pylori Eradication: 1 g twice daily with clarithromycin and lansoprazole for 14 days 7
Dosing Regimens
Adults
Standard dosing ranges from 750-1750 mg/day divided every 8-12 hours 7
- Most common infections: 500 mg three times daily or 875 mg twice daily
- High-dose therapy (for resistant pneumococcal infections): 4 g/day in divided doses 3
- Endocarditis prophylaxis: Single 2 g dose 11, 12
Pediatric Patients
Dosing should be weight-based rather than age-based to ensure appropriate mg/kg dosing 13, 14
- Standard dose: 20-45 mg/kg/day divided every 8-12 hours 7
- High-dose therapy: 80-90 mg/kg/day for resistant organisms 3, 14
- This is particularly important for pneumococcal infections with intermediate penicillin resistance
- Neonates and infants ≤3 months: Maximum 30 mg/kg/day divided every 12 hours 7
Critical dosing pitfall: Larger children frequently receive inadequate mg/kg dosing because clinicians are reluctant to exceed "adult maximum doses" 14. Children weighing >60 kg often receive <40 mg/kg/day when they should receive 80-90 mg/kg/day for appropriate indications 14.
Amoxicillin vs. Amoxicillin-Clavulanate
Use amoxicillin alone whenever possible to minimize adverse effects and preserve the effectiveness of β-lactamase inhibitors 15
When to Use Amoxicillin Alone
- Group A streptococcal pharyngitis 1, 2
- Community-acquired pneumonia (mild-to-moderate) 5
- Lyme disease 9
- Most skin infections caused by streptococci 6
When Amoxicillin-Clavulanate is Preferred
- Acute bacterial rhinosinusitis: Strong recommendation for children, weak recommendation for adults 4
- Acute otitis media with treatment failure on amoxicillin alone 3
- Infections likely caused by β-lactamase-producing organisms (H. influenzae, M. catarrhalis) 3
- Animal/human bites 15
Important consideration: Clavulanate increases gastrointestinal side effects (including Clostridioides difficile infection) and limits the maximum daily amoxicillin dose that can be administered 15. The 14:1 ratio formulation in children minimizes clavulanate exposure while maintaining β-lactamase inhibition 3.
Renal Dosing Adjustments
Reduce dosing in severe renal impairment (GFR <30 mL/min) 7
Key Precautions and Contraindications
Absolute Contraindications
- History of serious hypersensitivity reactions (anaphylaxis, Stevens-Johnson syndrome) to amoxicillin or other β-lactams 7
Warnings
- Anaphylactic reactions: Serious and occasionally fatal reactions have occurred with penicillin therapy 7
- Severe cutaneous adverse reactions (SCAR): Monitor closely and discontinue if rash progresses 7
- Clostridioides difficile-associated diarrhea: Evaluate any patient who develops diarrhea during or after treatment 7
Drug Interactions
- Probenecid: Coadministration not recommended (increases amoxicillin levels) 7
- Oral anticoagulants: May increase prothrombin time prolongation 7
- Allopurinol: Increases risk of rash 7
- Oral contraceptives: Amoxicillin may reduce efficacy 7
Special Populations
- Pregnancy: Safe to use; preferred over doxycycline for Lyme disease and chlamydial infections 9, 16
- Lactation: Compatible with breastfeeding 9
- Penicillin allergy: First-generation cephalosporins (cephalexin, cefadroxil) are alternatives if no immediate-type hypersensitivity 1, 2, 17