What is the recommended dose of cephalexin for skin and soft tissue infections?

Cephalexin Dosing for Skin and Soft Tissue Infections

For uncomplicated skin and soft tissue infections in adults, cephalexin 500 mg orally every 6 hours (four times daily) for 5-7 days is the recommended dose, but only when methicillin-resistant Staphylococcus aureus (MRSA) is not suspected. 1, 2, 3

Standard Adult Dosing

• The FDA-approved dose is 500 mg orally every 6 hours (four times daily) for skin and soft tissue infections 3
• Treatment duration should be 5 days minimum, extending to 7-10 days only if clinical improvement has not occurred within this timeframe 1, 2, 4
• The maximum daily dose is 4 grams per day 3
• An alternative dosing schedule of 500 mg every 12 hours may be used for mild infections, though the every-6-hour regimen is preferred for more significant infections 3

Pediatric Dosing

• The usual pediatric dose is 25-50 mg/kg/day divided into four doses (every 6 hours) 3
• For streptococcal pharyngitis and skin infections in children over 1 year, the total daily dose may be divided and given every 12 hours 3
• In severe infections, the pediatric dosage may be doubled 3

Critical Prescribing Considerations: When Cephalexin is Appropriate

Cephalexin should ONLY be used for non-purulent cellulitis without systemic signs of infection. 1, 2, 4 The IDSA guidelines emphasize that beta-lactam monotherapy (like cephalexin) achieves 96% success rates for typical cellulitis even in high MRSA prevalence areas, because most non-purulent cellulitis is caused by streptococci, not MRSA 4

Appropriate scenarios for cephalexin:

• Non-purulent cellulitis (no drainage, no abscess) 2, 4
• Confirmed methicillin-susceptible Staphylococcus aureus (MSSA) or streptococcal infections 1, 2
• No systemic signs of infection (temperature <38.5°C, heart rate <110 bpm, WBC <12,000) 2
• Penicillin-allergic patients (except those with immediate hypersensitivity reactions) 1, 2

When NOT to Use Cephalexin

Do not use cephalexin monotherapy when any MRSA risk factors are present—it is completely ineffective against MRSA. 2, 4 This is a critical pitfall that leads to treatment failure.

Absolute contraindications to cephalexin monotherapy:

• Purulent drainage or exudate present 2, 4
• Penetrating trauma or injection drug use 4
• Systemic inflammatory response syndrome (SIRS) or systemic signs of infection 2, 4
• History of MRSA colonization or previous MRSA infection 4
• Failed initial beta-lactam therapy 4
• Severely immunocompromised patients (malignancy on chemotherapy, neutropenia, severe immunodeficiency) 2
• Immersion injuries or animal bites 2
• Suspected necrotizing infection 1, 2

In these scenarios, use MRSA-active therapy instead:

• Add trimethoprim-sulfamethoxazole or doxycycline to the beta-lactam 1, 4
• Use clindamycin monotherapy 1, 4
• Use vancomycin for severe infections 1

Monitoring and Expected Response

• Clinical improvement should be evident within 48-72 hours of starting therapy 2
• If no improvement occurs within 72 hours, consider alternative diagnoses, resistant organisms (particularly MRSA), or deeper/necrotizing infection 2
• Complete the full 5-7 day course even if symptoms improve before completion 2
• Do not extend treatment beyond 5 days if clinical improvement has occurred—longer courses provide no additional benefit 4

Common Pitfalls to Avoid

1. Using cephalexin for purulent infections without considering MRSA is the most common error—purulent infections require MRSA-active antibiotics 2
2. Reflexively adding MRSA coverage simply because community-associated MRSA exists in the area—beta-lactam monotherapy remains highly effective for typical non-purulent cellulitis 4
3. Treating beyond 5-7 days when clinical improvement has occurred—this provides no additional benefit 4
4. Using cephalexin for necrotizing infections—these require immediate broad-spectrum IV antibiotics (vancomycin or linezolid plus piperacillin-tazobactam or a carbapenem) and urgent surgical intervention 1, 2

Special Populations

• Pregnancy: Cephalexin is FDA pregnancy category B and generally considered safe 2
• Penicillin allergy: Cephalexin is suitable for penicillin-allergic patients except those with immediate hypersensitivity reactions 1, 2

Adjunctive Measures

• Elevate the affected area 2
• Treat predisposing factors such as edema, obesity, eczema, venous insufficiency 2
• Carefully examine interdigital toe spaces in lower-extremity cellulitis to identify and treat tinea pedis or fissuring 2