What is the recommended dosing for amoxicillin in adults with bacterial infections?

Amoxicillin Dosing for Adults with Bacterial Infections

For most adult bacterial infections, amoxicillin should be dosed at 500 mg every 8 hours or 875 mg every 12 hours for mild-to-moderate infections, and 875 mg every 12 hours or 500 mg every 8 hours for severe infections, with treatment duration of 7-10 days for most indications. 1

Standard Dosing by Infection Severity

Mild-to-Moderate Infections

• Ear/Nose/Throat, Skin/Skin Structure, and Genitourinary Tract infections: 500 mg every 12 hours OR 250 mg every 8 hours 1
• Treatment should continue for a minimum of 48-72 hours beyond symptom resolution or evidence of bacterial eradication 1

Severe Infections

• All severe infections: 875 mg every 12 hours OR 500 mg every 8 hours 1
• Lower respiratory tract infections (any severity): 875 mg every 12 hours OR 500 mg every 8 hours 1

Specific Clinical Scenarios

Community-Acquired Pneumonia (Outpatient)

• Recommended dose: 1 gram (1000 mg) every 8 hours for patients without comorbidities 2
• This high-dose regimen has demonstrated efficacy in inpatient CAP studies and provides adequate coverage despite lack of atypical organism coverage 2
• The American Thoracic Society/IDSA guidelines support this dosing based on its long track record of safety and proven efficacy 2

Acute Bacterial Rhinosinusitis

For adults without risk factors:

• Standard amoxicillin: 1.5-4 grams per day divided into doses 2
• Treatment duration: 5-7 days 3

For adults with risk factors (recent antibiotic use within 4-6 weeks, treatment failure, daycare exposure, smoking, age >65, comorbidities, immunocompromised):

• Switch to amoxicillin-clavulanate rather than increasing amoxicillin dose alone 2, 3
• High-dose amoxicillin-clavulanate: 4 grams amoxicillin/250 mg clavulanate per day provides 90-92% predicted clinical efficacy 2

Streptococcal Pharyngitis

• Minimum treatment duration: 10 days for any Streptococcus pyogenes infection to prevent acute rheumatic fever 1
• Standard dosing applies (500 mg every 12 hours or 250 mg every 8 hours) 1

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: 1 gram amoxicillin three times daily (every 8 hours) with 30 mg lansoprazole for 14 days 1

Renal Impairment Dosing

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

• 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 an additional dose both during and at the end of dialysis 1

Administration Considerations

• Take at the start of a meal to minimize gastrointestinal intolerance 1
• For patients with recent exposure to one antibiotic class, select a different class to reduce resistance risk 2

Common Pitfalls to Avoid

• Do not use 875 mg dosing in severe renal impairment (GFR <30 mL/min), as this can lead to drug accumulation and toxicity 1
• Do not shorten treatment duration for streptococcal infections below 10 days, regardless of clinical improvement, to prevent rheumatic fever 1
• Do not assume standard dosing is adequate for resistant pathogens—consider switching to amoxicillin-clavulanate rather than increasing amoxicillin dose alone 2
• Recent evidence shows that high-dose amoxicillin-clavulanate (double amoxicillin) does not provide additional benefit over standard-dose amoxicillin-clavulanate for acute sinusitis in adults, with similar efficacy (44.3% vs 36.4% improvement at day 3, p=0.35) and similar rates of severe diarrhea 4