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

Proper Use and Dosage of Amoxicillin for Bacterial Infections

Amoxicillin is a first-line antibiotic for many common bacterial infections, with standard adult dosing of 500 mg every 12 hours or 250 mg every 8 hours for mild/moderate infections, and 875 mg every 12 hours or 500 mg every 8 hours for severe infections. 1

General Information

• Amoxicillin is a beta-lactam antibiotic (penicillin derivative) that works by inhibiting bacterial cell wall synthesis and producing autolysis 2
• It is relatively safe, well-tolerated, and has excellent bioavailability, making it one of the most active oral beta-lactams against streptococci, including pneumococci 2
• Should be taken at the start of a meal to minimize gastrointestinal intolerance 1

Dosage Guidelines for Adults

Standard Dosing by Infection Type:

• Mild/Moderate Ear/Nose/Throat, Skin/Skin Structure, Genitourinary Tract Infections:

  • 500 mg every 12 hours OR 250 mg every 8 hours 1

• Severe Ear/Nose/Throat, Skin/Skin Structure, Genitourinary Tract Infections:

  • 875 mg every 12 hours OR 500 mg every 8 hours 1

• Lower Respiratory Tract Infections (mild/moderate or severe):

  • 875 mg every 12 hours OR 500 mg every 8 hours 1

• H. pylori Infection (adults only):

  • Triple therapy: 1 gram amoxicillin twice daily (with 500 mg clarithromycin and 30 mg lansoprazole) for 14 days 1
  • Dual therapy: 1 gram amoxicillin three times daily (with 30 mg lansoprazole) for 14 days 1

• High-dose therapy (for resistant S. pneumoniae):

  • 4 g/day for adults (in divided doses) 2

Dosage Guidelines for Children

• Children ≥3 months and <40 kg:

  • Mild/Moderate infections: 25 mg/kg/day in divided doses every 12 hours OR 20 mg/kg/day in divided doses every 8 hours 1
  • Severe infections: 45 mg/kg/day in divided doses every 12 hours OR 40 mg/kg/day in divided doses every 8 hours 1
  • High-dose therapy: 90 mg/kg/day (for resistant S. pneumoniae) 2

• Children <12 weeks (3 months):

  • Maximum 30 mg/kg/day divided every 12 hours (due to incompletely developed renal function) 1

• For Acute Otitis Media:

  • 80-90 mg/kg/day in 2 divided doses 2

• For Community-Acquired Pneumonia in children <3 years:

  • 80-100 mg/kg/day in three daily intakes 2

Duration of Treatment

• Treatment should continue for a minimum of 48-72 hours beyond the time the patient becomes asymptomatic 1
• For Streptococcus pyogenes infections: minimum 10 days to prevent acute rheumatic fever 1
• For pneumococcal pneumonia: 10 days 2
• For atypical pneumonia: at least 14 days (with macrolide) 2

Dosage Adjustments for Renal Impairment

• Patients with GFR <30 mL/min should NOT receive the 875 mg dose 1
• For GFR 10-30 mL/min: 500 mg or 250 mg every 12 hours (depending on infection severity) 1
• For GFR <10 mL/min: 500 mg or 250 mg every 24 hours (depending on infection severity) 1
• For hemodialysis patients: 500 mg or 250 mg every 24 hours plus an additional dose during and at the end of dialysis 1

Specific Indications and Recommendations

Respiratory Tract Infections

• First-line for pneumococcal pneumonia due to excellent activity against S. pneumoniae 2
• For acute bacterial rhinosinusitis: High-dose amoxicillin (4 g/day for adults, 90 mg/kg/day for children) is recommended in areas with high prevalence of penicillin-resistant S. pneumoniae 2
• For H. influenzae infections: Consider amoxicillin-clavulanate if beta-lactamase producing strains are suspected 2

Streptococcal Pharyngitis

• Standard regimen: 500 mg three times daily for 10 days 2
• Alternative regimen: Once-daily dosing (750 mg once daily for 10 days) has shown similar efficacy to traditional multiple daily dosing regimens 3, 4

Skin and Soft Tissue Infections

• For erysipeloid: 500 mg three times daily for 7-10 days 2

Formulation and Administration

• Available as oral tablets and oral suspension 1
• Oral suspension must be reconstituted with specified amount of water 1
• After reconstitution, oral suspension must be discarded after 14 days 1
• Refrigeration of reconstituted suspension is preferable but not required 1

Common Adverse Effects

• Most common adverse reactions (>1%): diarrhea, rash, vomiting, and nausea 1
• Serious but rare reactions include anaphylaxis and severe cutaneous adverse reactions 1

Important Considerations

• Resistance to penicillin in S. pneumoniae is relative and can often be overcome with higher doses of amoxicillin 2
• Serum levels of amoxicillin increase linearly with the dose (gastrointestinal absorption is not a limiting factor) 2
• The difference in adverse effects between lower and higher doses is generally negligible 2
• Amoxicillin-clavulanate should be considered when beta-lactamase producing organisms are suspected (e.g., H. influenzae, M. catarrhalis) 2, 5

Pitfalls to Avoid

• Do not use amoxicillin alone for suspected beta-lactamase producing organisms (use amoxicillin-clavulanate instead) 2
• Do not use the 875 mg dose in patients with severe renal impairment (GFR <30 mL/min) 1
• Ensure adequate duration of therapy (minimum 10 days) for streptococcal infections to prevent acute rheumatic fever 1
• Monitor for allergic reactions, which can occasionally be severe 1
• Be aware of potential drug interactions, particularly with probenecid, oral anticoagulants, and allopurinol 1