What is the appropriate use of cephalexin (bid) for wound care?

Cephalexin for Wound Care: Dosing and Appropriate Use

Cephalexin should be dosed at 500 mg four times daily (every 6 hours), not twice daily, for wound infections caused by methicillin-susceptible Staphylococcus aureus (MSSA) and streptococci, with treatment duration of 7 days for most simple wounds. 1, 2, 3

Critical Dosing Error: BID is Inadequate

• The standard recommended dosing is 500 mg QID (four times daily), not BID (twice daily). 1, 2, 3
• While one older study from 1981 suggested twice-daily dosing might be effective for some soft tissue infections 4, this contradicts current IDSA guidelines which explicitly recommend four times daily dosing for skin and soft tissue infections. 1, 2
• The Infectious Diseases Society of America guidelines specify 500 mg every 6 hours (QID) to maintain adequate tissue concentrations against staphylococcal infections. 2, 3

When Cephalexin is Appropriate for Wound Care

Suitable Wound Types

• Simple, non-purulent cellulitis or erysipelas caused by MSSA or streptococci in immunocompetent patients. 1
• Mild impetigo or ecthyma when MSSA is suspected (7-day course recommended). 1
• Simple traumatic contaminated wounds requiring prophylaxis after primary closure—though only 2 days of prophylaxis is needed, not prolonged courses. 5
• Surgical site infections of the trunk or extremities (away from axilla/perineum) when MSSA is the likely pathogen. 1

Duration of Therapy

• 7 days for most skin and soft tissue infections including impetigo and simple wound infections. 1, 3
• Only 2 days for prophylactic use in contaminated traumatic wounds—a 2-day regimen is as effective as 5 days for preventing infection. 5
• At least 10 days for streptococcal infections to prevent rheumatic fever complications. 3

Critical Situations Where Cephalexin is INADEQUATE

MRSA Infections

• Cephalexin has zero activity against MRSA and will fail if methicillin-resistant S. aureus is present. 1, 2
• If MRSA is suspected or confirmed, switch immediately to trimethoprim-sulfamethoxazole, doxycycline, or clindamycin. 1, 2

Bite Wounds

• Cephalexin alone is inadequate for animal bites due to poor coverage of Pasteurella multocida, which is present in dog and cat bites. 1, 2
• Cephalexin is inadequate for human bites because it misses Eikenella corrodens, which is resistant to first-generation cephalosporins. 1, 2
• For bite wounds, amoxicillin-clavulanate is the preferred oral agent. 1

Anaerobic or Deep Infections

• Cephalexin has limited anaerobic coverage and should not be used for deep abscesses, necrotizing infections, or wounds involving the perineum or gastrointestinal tract. 1, 2, 3
• For surgical site infections of the axilla or perineum, combination therapy with metronidazole or broader agents is required. 1

Purulent Infections Requiring Drainage

• Incision and drainage is the primary treatment for purulent SSTIs (abscesses, furuncles, carbuncles). 1
• Antibiotics including cephalexin are adjunctive and should not replace surgical drainage. 1

Microbiological Coverage Limitations

• Excellent activity: MSSA, Streptococcus pyogenes, and other streptococci. 2, 6
• Poor or no activity: MRSA, Pasteurella multocida, Eikenella corrodens, Haemophilus influenzae, Moraxella catarrhalis, Pseudomonas aeruginosa, and most anaerobes. 2, 3

Practical Prescribing Considerations

Renal Impairment

• Dose reduction is required when creatinine clearance falls below 30 mL/min since cephalexin is renally cleared with 70-100% excreted unchanged in urine. 7, 6

Penicillin Allergy

• Cephalexin can be used in patients with non-severe penicillin reactions (e.g., delayed rash), but is contraindicated in those with immediate hypersensitivity (anaphylaxis, urticaria, angioedema). 2, 3

Drug Interactions

• Monitor metformin closely if co-administered, as cephalexin increases metformin levels by 24-34% through inhibition of renal tubular secretion. 7
• Probenecid inhibits cephalexin excretion, increasing serum levels. 7

Patient Counseling

• Complete the full course even if symptoms improve early to prevent resistance development. 7
• Watch for Clostridioides difficile infection—watery or bloody diarrhea can occur up to 2 months after treatment. 7

When to Escalate Therapy

• If doses exceeding 4 grams daily are needed, switch to parenteral cefazolin (1 g IV every 8 hours) rather than increasing oral cephalexin. 3
• If no clinical improvement within 48-72 hours, consider MRSA, inadequate source control (undrained abscess), or resistant organisms. 1, 8