What is the appropriate dosage and treatment duration of Amoxicillin for a patient with a confirmed bacterial infection?

Amoxicillin Dosing and Treatment Duration for Bacterial Infections

For most bacterial infections in adults, amoxicillin should be dosed at 500 mg every 8 hours or 875 mg every 12 hours for mild-to-moderate infections, with treatment continued for a minimum of 48-72 hours beyond symptom resolution, and at least 10 days for streptococcal infections. 1

Adult Dosing Guidelines

Standard Dosing by Infection Severity

Mild-to-Moderate Infections:

• 500 mg every 12 hours OR 250 mg every 8 hours for ear/nose/throat, skin/skin structure, and genitourinary tract infections 1
• This lower-dose regimen is appropriate when there are no risk factors for resistant pathogens 2

Severe Infections:

• 875 mg every 12 hours OR 500 mg every 8 hours for more severe presentations 1
• Lower respiratory tract infections require 875 mg every 12 hours OR 500 mg every 8 hours regardless of severity 1

High-Dose Regimens for Resistant Organisms

When penicillin-resistant Streptococcus pneumoniae is suspected:

• Amoxicillin 1.5-4 g/day is recommended, with higher doses (4 g/day) indicated for areas with high prevalence of drug-resistant S. pneumoniae (DRSP) 2
• Risk factors requiring high-dose therapy include: recent antimicrobial use (within 4-6 weeks), immunodeficiency, frequent daycare exposure, and moderate disease severity 2

For acute bacterial rhinosinusitis with resistance risk:

• Amoxicillin/clavulanate 4 g/250 mg daily provides 91% clinical efficacy and 99% bacteriologic efficacy 2

Pediatric Dosing Guidelines

Weight-Based Dosing by Severity

Standard-Dose Regimen (Children ≥3 months, <40 kg):

• Mild-to-moderate infections: 25 mg/kg/day divided every 12 hours OR 20 mg/kg/day divided every 8 hours 1
• This is appropriate for children ≥2 years without recent antibiotic use and not attending daycare 3

High-Dose Regimen:

• Severe infections: 45 mg/kg/day divided every 12 hours OR 40 mg/kg/day divided every 8 hours 1
• Lower respiratory tract infections require 45 mg/kg/day divided every 12 hours OR 40 mg/kg/day divided every 8 hours regardless of severity 1

Indications for High-Dose Pediatric Therapy (80-90 mg/kg/day)

High-dose amoxicillin (80-90 mg/kg/day) is indicated for: 3

• Children <2 years of age
• Daycare attendance
• Recent antibiotic use (within 30 days)
• Moderate-to-severe illness
• Communities with >10% penicillin-nonsusceptible S. pneumoniae

The American Academy of Pediatrics supports high-dose amoxicillin-clavulanate (90 mg/kg/day amoxicillin component with 6.4 mg/kg clavulanate) for resistant organisms, not to exceed 2 g every 12 hours 3

Neonates and Infants <3 Months

Maximum dose: 30 mg/kg/day divided every 12 hours due to incompletely developed renal function 1

Treatment Duration by Infection Type

Minimum Duration Requirements

All bacterial infections:

• Continue treatment for a minimum of 48-72 hours beyond symptom resolution or evidence of bacterial eradication 1

Streptococcal infections (any site):

• Minimum 10 days of treatment is mandatory to prevent acute rheumatic fever 1, 3
• This applies even if symptoms resolve earlier 3

Acute otitis media and sinusitis in children:

• 10-14 days of therapy 3

Community-acquired pneumonia in children:

• 5 days of amoxicillin is as effective as 10 days for uncomplicated cases in outpatient settings (clinical cure rates equivalent: RR 1.01,95% CI 0.98-1.05) 4
• Pneumococcal pneumonia: 10 days with beta-lactam 2
• Atypical pneumonia: at least 14 days with macrolide 2

Acute bacterial rhinosinusitis:

• 10-14 days for standard treatment 3

Reassessment Timeline

Clinical response should be assessed at 48-72 hours (or 3-5 days for sinusitis): 2, 3, 5

• Failure to improve or worsening symptoms indicates need for alternative therapy
• Switch to a different antibiotic class rather than simply extending duration 5
• Consider limitations in coverage of the initial agent when changing therapy 2

Special Populations

Renal Impairment

GFR 10-30 mL/min:

• 500 mg or 250 mg every 12 hours depending on infection severity 1

GFR <10 mL/min:

• 500 mg or 250 mg every 24 hours depending on infection severity 1

Hemodialysis:

• 500 mg or 250 mg every 24 hours, with additional dose during and at end of dialysis 1

Important caveat: Patients with GFR <30 mL/min should NOT receive the 875 mg dose 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 (for clarithromycin allergy/resistance):

• 1 gram amoxicillin + 30 mg lansoprazole, both three times daily for 14 days 1

Critical Administration Considerations

Timing and Food

Amoxicillin should be taken at the start of a meal to minimize gastrointestinal intolerance 1

Common Pitfall to Avoid

Never substitute two 250 mg tablets for one 500 mg tablet when using amoxicillin-clavulanate formulations, as this results in excessive clavulanate dosing and increased gastrointestinal side effects 3

Oral Suspension Preparation

• Shake bottle until powder flows freely, add 1/3 of required water, shake vigorously, add remaining water, shake again 1
• Shake well before each use 1
• Discard unused suspension after 14 days 1
• Refrigeration is preferable but not required 1

When to Switch Therapy

Failure to respond after 72 hours indicates: 2

• Need for alternative antimicrobial with broader coverage
• Possible beta-lactamase-producing organisms if not initially covered
• Consideration of respiratory fluoroquinolones (gatifloxacin, levofloxacin, moxifloxacin) for adults 2
• High-dose amoxicillin alone (80-90 mg/kg/day in children, 1500-4000 mg/day in adults) if beta-lactamase producers are not suspected 5