What is the dosage of Keflex (cephalexin) for treating strep throat?

Keflex (Cephalexin) Dosing for Strep Throat

For strep throat, adults should take cephalexin 500 mg orally every 12 hours for 10 days, and children should receive 25-50 mg/kg/day divided into doses every 12 hours for 10 days. 1

Adult Dosing

• The FDA-approved regimen is 500 mg every 12 hours (twice daily) for streptococcal pharyngitis 1
• The total daily dose ranges from 1-4 grams, but 500 mg twice daily (1 gram total daily) is specifically indicated for strep throat 1
• The full 10-day course must be completed to achieve maximal pharyngeal eradication of Group A Streptococcus and prevent acute rheumatic fever 2

Pediatric Dosing

• The recommended dose is 25-50 mg/kg/day divided every 12 hours for children over 1 year of age 1
• For streptococcal pharyngitis specifically, the total daily dose may be divided and administered twice daily rather than four times daily 1
• A therapeutic dosage must be administered for at least 10 days for β-hemolytic streptococcal infections 1

When to Use Cephalexin for Strep Throat

Cephalexin is NOT first-line therapy for strep throat. Penicillin or amoxicillin remains the drug of choice due to proven efficacy, narrow spectrum, safety, and low cost 2

Cephalexin should be used for:

• Patients with non-immediate (non-anaphylactic) penicillin allergy 2
• Patients who cannot tolerate penicillin or amoxicillin for other reasons 2

Critical Safety Consideration

Avoid cephalexin in patients with immediate/anaphylactic penicillin reactions (hives, angioedema, bronchospasm within 1 hour of penicillin) due to up to 10% cross-reactivity risk 2

For these patients, use clindamycin 300-400 mg four times daily for adults or 20 mg/kg/day in 3 divided doses for children, or azithromycin 500 mg once daily for 5 days in adults or 12 mg/kg once daily for 5 days in children 3, 2

Evidence Supporting Twice-Daily Dosing

• Clinical studies demonstrate that twice-daily cephalexin is equally effective as four-times-daily dosing for strep throat, with failure rates of 7.3% vs 5.3% respectively (not statistically different) 4
• Cephalexin has shown superior efficacy compared to penicillin in some studies, with combined treatment failure rates of 10% vs 19% 5
• The twice-daily regimen improves adherence while maintaining therapeutic efficacy 4

Common Pitfalls to Avoid

• Never shorten the course below 10 days despite clinical improvement—symptoms typically resolve in 3-4 days, but full course completion is essential to prevent acute rheumatic fever 2
• Do not use cephalexin as first-line therapy when penicillin or amoxicillin can be used—this unnecessarily broadens antibiotic spectrum and increases cost 2
• Do not prescribe to patients with documented immediate penicillin hypersensitivity—the cross-reactivity risk is too high 2