What is the proper use and dosage of Amoxicillin (amoxicillin)?

Amoxicillin: Proper Use and Dosage

Amoxicillin is a broad-spectrum penicillin antibiotic used primarily for respiratory, ear, skin, and urinary tract infections, with standard adult dosing of 500 mg every 8 hours or 875 mg every 12 hours for most infections, and pediatric dosing of 25-45 mg/kg/day divided into 2-3 doses depending on severity. 1

Adult Dosing

Standard Infections

• Mild to moderate infections (ear/nose/throat, skin, genitourinary): 500 mg every 12 hours or 250 mg every 8 hours 1
• Severe infections or lower respiratory tract infections: 875 mg every 12 hours or 500 mg every 8 hours 1
• Treatment should continue for minimum 48-72 hours beyond symptom resolution 1

Specific Indications

• Acute bacterial sinusitis: 500 mg three times daily for 5-7 days 2
• Erysipeloid: 500 mg four times daily for 7-10 days 2
• H. pylori eradication (triple therapy): 1 gram twice daily with clarithromycin 500 mg and lansoprazole 30 mg for 14 days 1
• H. pylori eradication (dual therapy): 1 gram three times daily with lansoprazole 30 mg for 14 days 1

Pediatric Dosing (≥3 Months and <40 kg)

Age-Based Dosing

• Mild to moderate infections: 25 mg/kg/day divided every 12 hours OR 20 mg/kg/day divided every 8 hours 1
• Severe infections or lower respiratory tract: 45 mg/kg/day divided every 12 hours OR 40 mg/kg/day divided every 8 hours 1

Specific Pediatric Conditions

• Community-acquired pneumonia (children <3 years): 80-100 mg/kg/day in 3 divided doses for 10 days 2
• Acute otitis media: 80-90 mg/kg/day in 2 divided doses for high-risk patients (daycare attendance, recent antibiotic use, age <2 years) 2
• Infants <12 weeks: Maximum 30 mg/kg/day divided every 12 hours due to immature renal function 1

Important Clinical Considerations

When to Use Amoxicillin-Clavulanate Instead

Amoxicillin-clavulanate should be used instead of amoxicillin alone in the following situations:

• Recent antibiotic use within 30 days 2, 3
• Concurrent purulent conjunctivitis 2
• Coverage needed for β-lactamase-producing organisms (H. influenzae, M. catarrhalis) 2
• Treatment failure with amoxicillin after 48-72 hours 2
• Incomplete H. influenzae type b vaccination (<3 injections) 2

Renal Dosing 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
• Hemodialysis: 500 mg or 250 mg every 24 hours, with additional dose during and after dialysis 1
• Do NOT use 875 mg dose if GFR <30 mL/min 1

Duration of Therapy

• Most infections: 5-10 days, with minimum 48-72 hours beyond symptom resolution 1
• Streptococcus pyogenes infections: Minimum 10 days to prevent acute rheumatic fever 1
• Uncomplicated pneumonia: 5 days may be as effective as 10 days in children 4
• Sinusitis: 5-7 days is as effective as 10 days 3

Administration Guidelines

• Take at the start of meals to minimize gastrointestinal intolerance 1
• Oral suspension must be shaken well before use 1
• Reconstituted suspension expires after 14 days; refrigeration preferred but not required 1

Common Pitfalls to Avoid

• Avoid monotherapy for acne - should only be used as adjunctive treatment 2
• Do not use standard doses when high-dose therapy is indicated - leads to treatment failure with resistant organisms 5
• Ensure adequate duration for S. pyogenes - incomplete courses risk rheumatic fever 1
• Amoxicillin is destroyed by β-lactamases, so it is ineffective against β-lactamase-producing organisms without clavulanate 6

Contraindications and Precautions

• Absolute contraindication: Known hypersensitivity to penicillins, including anaphylaxis or Stevens-Johnson syndrome 2
• Cross-reactivity with cephalosporins is lower than historically reported (previously overestimated at 10%) 2
• Pregnancy category B - generally safe during pregnancy 2
• Compatible with breastfeeding with minimal risk to infant 2