What is the recommended dose and duration of Keflex (Cephalexin) for a typical adult patient with an uncomplicated skin wound?

Cephalexin Dosing for Skin Wounds

For an uncomplicated skin wound in adults, prescribe cephalexin 500 mg orally four times daily (every 6 hours) for 7 days. 1, 2, 3

Standard Adult Dosing Regimen

• The recommended dose is 500 mg four times daily (every 6 hours) for skin and soft tissue infections, particularly those caused by methicillin-susceptible Staphylococcus aureus (MSSA) and Streptococcus species. 1, 2, 3

• The FDA-approved dosing range for adults is 1 to 4 grams daily in divided doses, with the usual adult dose being 250 mg every 6 hours, though 500 mg every 12 hours may be used for uncomplicated skin infections. 3

• For more severe infections or less susceptible organisms, the 500 mg four times daily regimen provides superior tissue concentrations. 2, 3

Duration of Treatment

• The typical treatment duration is 7 days for uncomplicated skin wounds, with extension to 10 days if clinical improvement is not evident by day 5. 2, 4, 5

• If the infection has not improved within 5 days, treatment should be extended beyond the initial 7-day course. 4

• Clinical studies comparing cephalexin to other antibiotics for uncomplicated skin infections consistently used 7-10 day treatment courses with excellent outcomes. 5, 6, 7

Microbiological Coverage and Critical Limitations

Cephalexin provides excellent activity against methicillin-susceptible Staphylococcus aureus (MSSA) and Streptococcus species, but is completely ineffective against MRSA. 1, 2, 4

When Cephalexin is Appropriate:

• Uncomplicated skin wounds with no risk factors for MRSA 1, 2
• Infections caused by Streptococcus species 1, 2
• Simple cellulitis, wound infections, and abscesses (after drainage) caused by MSSA 4, 5

When to Avoid Cephalexin:

• If MRSA is suspected or confirmed, switch immediately to trimethoprim-sulfamethoxazole, doxycycline, or clindamycin as cephalexin has no activity against methicillin-resistant organisms. 1, 4

• Cephalexin has poor activity against Pasteurella multocida (animal bites), Eikenella corrodens (human bites), and most anaerobes, making it unsuitable for bite wounds or deep abscesses without drainage. 1, 2, 4

• Cephalexin is ineffective against Pseudomonas aeruginosa, Haemophilus influenzae, and beta-lactamase-producing Moraxella catarrhalis. 2

Practical Administration Details

• Administer at consistent 6-hour intervals (e.g., 6:00 AM, 12:00 PM, 6:00 PM, 12:00 AM) to maintain therapeutic drug levels. 2

• The medication can be taken with or without food, though taking it with food may reduce gastrointestinal side effects. 3

• If daily doses exceeding 4 grams are required for severe infections, switch to parenteral cephalosporins (e.g., cefazolin 1 g IV every 8 hours) rather than increasing oral cephalexin. 2, 3

Pediatric Dosing

• For children with uncomplicated skin wounds, the recommended dose is 25-50 mg/kg/day divided into 4 doses (every 6 hours). 2, 3

• For MSSA infections in children, increase to 75-100 mg/kg/day divided into 3-4 doses. 1, 2, 3

• The FDA label provides weight-based dosing tables: for a 20 kg child with mild infection, give 1-2 teaspoons of 125 mg/5 mL suspension four times daily. 3

Common Pitfalls to Avoid

Do not use cephalexin for wounds with purulent drainage unless MRSA has been ruled out by culture, as community-associated MRSA now accounts for up to 69% of skin and soft tissue infections in some regions. 8

• Patients with immediate hypersensitivity reactions (anaphylaxis, angioedema, urticaria) to penicillin should avoid cephalexin due to potential cross-reactivity, though non-immediate reactions are generally safe. 1, 4

• Ensure adequate wound drainage before initiating antibiotics - a 2011 pediatric study showed that drainage procedures were performed in 97% of successfully treated cases, suggesting that proper wound care may be more important than antibiotic choice for uncomplicated infections. 8

• For simple skin abrasions without signs of significant infection (no erythema, warmth, purulent drainage, or systemic symptoms), topical antimicrobial agents may be sufficient without systemic antibiotics. 4

Monitoring and Follow-up

• Reassess clinical response at 48-72 hours; if no improvement is seen, consider MRSA coverage or broader-spectrum antibiotics. 4, 8

• Fevers and age less than 1 year are associated with early treatment failures regardless of antibiotic choice, warranting closer monitoring. 8

• The most common adverse events are diarrhea (4-10%), nausea (3-6%), and headache, with only 3-4% of patients discontinuing due to side effects. 5, 7