What is the recommended dosage and treatment duration of cephalexin (cephalexin) for an adult patient with strep throat?

Cephalexin for Strep Throat in Adults

For adults with confirmed Group A streptococcal pharyngitis, cephalexin 500 mg orally twice daily for 10 days is the recommended dosage when a first-generation cephalosporin is indicated, typically reserved for patients with non-anaphylactic penicillin allergy. 1, 2

Critical Context: Cephalexin is NOT First-Line Therapy

• Penicillin or amoxicillin remains the drug of choice for strep throat in non-allergic patients due to proven efficacy, narrow spectrum, safety, and low cost 3, 1
• Cephalexin should be reserved specifically for patients with non-immediate (non-anaphylactic) penicillin allergy 1
• Patients with immediate hypersensitivity reactions to penicillin (anaphylaxis, angioedema, urticaria within 1 hour) must avoid ALL cephalosporins due to up to 10% cross-reactivity risk 1

Specific Dosing Regimen

• Adult dose: 500 mg orally every 12 hours for 10 days 1, 2
• The FDA label also approves 250 mg every 6 hours, but the twice-daily regimen improves compliance with equivalent efficacy 2, 4
• The full 10-day course is mandatory to achieve maximal pharyngeal eradication of Group A Streptococcus and prevent acute rheumatic fever 1, 5

Why the Full 10-Day Course Matters

• Prevention of acute rheumatic fever requires adequate bacterial eradication, not just symptom relief 1, 6
• Symptoms typically resolve in 3-4 days without treatment, but completing the full course is essential for preventing complications 1
• Shortening the course by even a few days results in appreciable increases in treatment failure rates and rheumatic fever risk 1, 6

Evidence Supporting Cephalexin Efficacy

• First-generation cephalosporins have strong, high-quality evidence for efficacy in streptococcal pharyngitis 1
• Clinical studies demonstrate cephalexin achieves 96.7% cure rates, comparable to penicillin 7
• Cephalosporins may have slightly better bacterial eradication rates than penicillin, though clinical differences are small 1

When to Use Alternative Antibiotics Instead

For immediate/anaphylactic penicillin allergy:

• Clindamycin 300 mg orally three times daily for 10 days is the preferred choice 1, 5
• Clindamycin has only ~1% resistance among Group A Streptococcus in the United States and demonstrates high efficacy even in chronic carriers 1

For macrolide alternatives:

• Azithromycin 500 mg on day 1, then 250 mg daily for 4 days (5-day total course) 1, 5
• Clarithromycin 250 mg twice daily for 10 days 1, 5
• Be aware that macrolide resistance is 5-8% in the United States and varies geographically 1

Common Pitfalls to Avoid

• Do not use cephalexin if the patient had anaphylaxis, angioedema, or immediate urticaria to penicillin due to 10% cross-reactivity risk 1
• Do not prescribe broad-spectrum cephalosporins (cefdinir, cefuroxime) when narrow-spectrum cephalexin is appropriate—they are more expensive and select for resistant flora 1
• Do not shorten the treatment course below 10 days despite symptom improvement 1, 6
• Do not order routine post-treatment throat cultures for asymptomatic patients who completed therapy 1

Adjunctive Symptomatic Treatment

• Offer acetaminophen or NSAIDs (ibuprofen) for moderate to severe symptoms or high fever 1
• Patients become non-contagious after 24 hours of appropriate antibiotic therapy 6
• Corticosteroids are not recommended as adjunctive therapy 6