What is the dosage and treatment plan for Amoxicillin (amoxacillin) for bacterial infections?

Amoxicillin Dosing and Treatment Guidelines for Bacterial Infections

For most bacterial infections in adults and children ≥3 months weighing <40 kg, amoxicillin should be dosed at 25 mg/kg/day divided every 12 hours (or 20 mg/kg/day divided every 8 hours) for mild-to-moderate infections, and 45 mg/kg/day divided every 12 hours (or 40 mg/kg/day divided every 8 hours) for severe infections, with treatment duration of 48-72 hours beyond symptom resolution. 1

Adult Dosing by Infection Severity

Mild to Moderate Infections

• Standard dose: 500 mg every 12 hours or 250 mg every 8 hours for ear/nose/throat, skin/skin structure, and genitourinary tract infections 1
• Maximum daily dose: Do not exceed 4000 mg/day 2

Severe Infections

• High dose: 875 mg every 12 hours or 500 mg every 8 hours 1
• For lower respiratory tract infections (regardless of severity), use 875 mg every 12 hours or 500 mg every 8 hours 1

Acute Bacterial Rhinosinusitis

• Mild disease without recent antibiotic use: 1.5 g/day (standard dose) 3, 2
• Moderate disease or high-risk areas: 4 g/day divided in 2 doses to overcome penicillin-resistant S. pneumoniae 3, 2
• High-dose therapy achieves adequate sinus fluid concentrations to overcome resistance 3

Pediatric Dosing (≥3 Months and <40 kg)

Standard Dosing

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

Acute Bacterial Sinusitis in Children

• Low-risk children ≥2 years (no daycare, no recent antibiotics): 45 mg/kg/day in 2 divided doses 3
• High-risk children (<2 years, daycare attendance, recent antibiotics): 80-90 mg/kg/day in 2 divided doses (maximum 2 g per dose) 3
• This high-dose regimen overcomes penicillin-resistant S. pneumoniae and β-lactamase-producing H. influenzae 3

Infants <3 Months (12 Weeks)

• Maximum dose: 30 mg/kg/day divided every 12 hours due to immature renal function 1
• Treatment duration: minimum 48-72 hours beyond symptom resolution 1

Special Clinical Situations

Renal Impairment

• GFR 10-30 mL/min: 500 mg or 250 mg every 12 hours (depending on severity) 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
• Important: Do NOT use 875 mg dose if GFR <30 mL/min 1

Helicobacter pylori Infection (Adults Only)

• Triple therapy: 1 gram amoxicillin + 500 mg clarithromycin + 30 mg lansoprazole, all twice daily for 14 days 1
• Dual therapy (clarithromycin-allergic): 1 gram amoxicillin + 30 mg lansoprazole, both three times daily for 14 days 1

Streptococcal Infections

• Minimum treatment duration: 10 days for Streptococcus pyogenes to prevent acute rheumatic fever 1
• Once-daily dosing is non-inferior to multiple daily doses for streptococcal pharyngitis, which may improve compliance 4

Treatment Duration Guidelines

• Standard bacterial infections: Continue for minimum 48-72 hours beyond symptom resolution or bacterial eradication 1
• Streptococcal infections: Minimum 10 days 1
• Uncomplicated UTIs: 3-7 days 5
• Some infections may require several weeks of therapy with clinical/bacteriological follow-up for several months after cessation 1

Administration Recommendations

• Take at the start of a meal to minimize gastrointestinal intolerance 1
• For oral suspension: shake well before using; refrigeration preferable but not required; discard after 14 days 1
• Can be mixed with formula, milk, fruit juice, water, or cold drinks for children (administer immediately) 1

Key Clinical Considerations

When to Use High-Dose Amoxicillin

• Geographic areas with >10% penicillin-resistant S. pneumoniae prevalence 3
• Children <2 years of age 3
• Daycare attendance 3
• Recent antibiotic use within 4-6 weeks 3
• Moderate to severe disease 3

Resistance Patterns

• Amoxicillin maintains excellent activity against S. pneumoniae (MIC90 0.06 μg/mL) and S. suis 6
• 10-15% of S. pneumoniae isolates nationally are penicillin-nonsusceptible, but can reach 50-60% in some areas 3
• 10-42% of H. influenzae are β-lactamase positive and require amoxicillin-clavulanate 3
• Nearly 100% of M. catarrhalis are β-lactamase positive 3

When Amoxicillin Alone Is Insufficient

• For β-lactamase-producing organisms (H. influenzae, M. catarrhalis), switch to amoxicillin-clavulanate 3
• For E. coli infections, 70.9% show reduced susceptibility; consider amoxicillin-clavulanate 6
• If no improvement after 72 hours, reevaluate and consider switching therapy 3

Pregnancy and Breastfeeding

• Pregnancy Category B: Compatible with use during pregnancy 2
• Breastfeeding: Compatible with minimal risk to infant, though distributed into milk; use with caution 2