What is the proper use and dosage of Amoxicillin (Amoxicillin) for treating bacterial infections?

Amoxicillin Treatment Guidelines for Bacterial Infections

Indications and First-Line Use

Amoxicillin is the first-line antibiotic for most common bacterial infections in both adults and children, including upper respiratory tract infections, skin infections, genitourinary infections, and community-acquired pneumonia. 1

FDA-Approved Indications

• Upper respiratory tract infections (ear, nose, throat) 1
• Lower respiratory tract infections 1
• Skin and skin structure infections 1
• Genitourinary tract infections 1
• H. pylori infection and duodenal ulcer disease (adults only) 1

Adult Dosing Recommendations

Standard Infections

For mild to moderate infections in adults, use 500 mg every 12 hours or 250 mg every 8 hours. 1

For severe infections or lower respiratory tract infections, use 875 mg every 12 hours or 500 mg every 8 hours. 1

Specific Infection Types

Acute Bacterial Rhinosinusitis

• Mild disease without recent antibiotic use (past 4-6 weeks): Amoxicillin 1.5-4 g/day 2
• For patients at risk for drug-resistant S. pneumoniae (recent antibiotic use, daycare exposure, immunodeficiency): High-dose amoxicillin/clavulanate 4 g/250 mg per day 2
• Switch therapy if no improvement after 72 hours 2

H. pylori Infection

• Triple therapy: 1 gram amoxicillin twice daily (every 12 hours) with 500 mg clarithromycin and 30 mg lansoprazole for 14 days 1
• Dual therapy (for clarithromycin allergy/resistance): 1 gram amoxicillin three times daily (every 8 hours) with 30 mg lansoprazole for 14 days 1

Pediatric Dosing Recommendations

Children ≥3 Months and <40 kg

For mild to moderate ear/nose/throat, skin, or genitourinary infections: 25 mg/kg/day divided every 12 hours or 20 mg/kg/day divided every 8 hours 1

For severe infections or any lower respiratory tract infection: 45 mg/kg/day divided every 12 hours or 40 mg/kg/day divided every 8 hours 1

Infants <3 Months (12 Weeks)

Maximum dose is 30 mg/kg/day divided every 12 hours due to immature renal function 1

Specific Pediatric Conditions

Community-Acquired Pneumonia

• Children <3 years: High-dose amoxicillin 90 mg/kg/day in three divided doses (maximum 4000 mg/day) 2
• Children ≥3 years with suspected pneumococcal pneumonia: 90 mg/kg/day 2
• Children ≥3 years with suspected atypical pneumonia (Mycoplasma, Chlamydia): Use macrolide instead 2
• Treatment duration: 10 days for pneumococcal pneumonia 2

Acute Bacterial Sinusitis

• Children ≥2 years with mild-moderate disease and no recent antibiotics: Standard-dose amoxicillin 45 mg/kg/day in 2 divided doses 2
• Children <2 years, in daycare, or with recent antibiotic use: High-dose amoxicillin 80-90 mg/kg/day in 2 divided doses (maximum 2 g/dose) 2
• Alternative for severe disease or treatment failure: High-dose amoxicillin/clavulanate 90 mg/kg/day (of amoxicillin component) with 6.4 mg/kg/day clavulanate 2

Acute Bronchiolitis

• Antibiotics generally not indicated 2
• Consider amoxicillin/clavulanate only if fever ≥38.5°C persists >3 days, purulent otitis media present, or pneumonia confirmed on chest X-ray 2

Administration Guidelines

Take amoxicillin at the start of a meal to minimize gastrointestinal intolerance 1

Oral Suspension Preparation

• Reconstitute powder with specified amount of water per bottle size 1
• Shake vigorously after adding water 1
• Shake well before each use 1
• Discard unused suspension after 14 days 1
• Refrigeration preferable but not required 1

Treatment Duration

Continue treatment for minimum 48-72 hours beyond symptom resolution or bacterial eradication 1

For Streptococcus pyogenes infections: Minimum 10 days to prevent acute rheumatic fever 1

Specific durations:

• Acute bacterial sinusitis: 10 days 2
• Pneumococcal pneumonia: 10 days 2
• Atypical pneumonia: 14 days (use macrolide) 2

Renal Impairment Dosing

Patients with GFR <30 mL/min should NOT receive the 875 mg dose 1

Severe Renal Impairment (Adults and Children >40 kg)

• 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 at end of dialysis 1

When to Switch or Escalate Therapy

Failure Criteria

If no improvement after 72 hours, switch to alternative antibiotic or reevaluate patient 2

Switch Options for Amoxicillin Failure

• Respiratory fluoroquinolone (levofloxacin, moxifloxacin) 2
• High-dose amoxicillin/clavulanate 4 g/250 mg daily 2
• Ceftriaxone 1 g/day IM or IV for 5 days 2

Pediatric Switch Options

• Amoxicillin failure after 48 hours suggests atypical bacteria; switch to macrolide monotherapy 2
• For vomiting or inability to take oral medication: Single dose ceftriaxone 50 mg/kg IV/IM, then reassess at 24 hours 2

Important Caveats and Pitfalls

Penicillin Allergy Considerations

Recent evidence shows risk of serious allergic reaction to second- and third-generation cephalosporins in penicillin-allergic patients is negligible 2

For true Type I hypersensitivity:

• Adults: Use respiratory fluoroquinolone, doxycycline, or TMP/SMX 2
• Children: Use levofloxacin, moxifloxacin, or linezolid 2

Resistance Considerations

Risk factors for resistant organisms include:

• Antibiotic use within past 4-6 weeks 2
• Age <2 years 2
• Daycare attendance 2
• Immunodeficiency 2

In these situations, use high-dose amoxicillin (90 mg/kg/day in children, 4 g/day in adults) or amoxicillin/clavulanate 2

Geographic Variability

Local resistance patterns vary significantly; 10-60% of S. pneumoniae may be penicillin-nonsusceptible depending on location 2

10-42% of H. influenzae are β-lactamase positive and require amoxicillin/clavulanate 2

Contraindications

Do not use amoxicillin in patients with history of serious hypersensitivity reaction (anaphylaxis, Stevens-Johnson syndrome) to amoxicillin or other β-lactams 1