Oral Cephalexin (Keflex) for Uncomplicated Hand Cellulitis Without MRSA Risk Factors
Yes, oral cephalexin 500 mg four times daily for 5 days is the appropriate first-line treatment for uncomplicated, non-purulent cellulitis of the hand in patients without MRSA risk factors. 1, 2
Why Cephalexin Is the Correct Choice
Non-purulent cellulitis (erythema, warmth, swelling, tenderness without purulent drainage or abscess) is predominantly caused by β-hemolytic streptococci and methicillin-susceptible Staphylococcus aureus, not MRSA. 1, 2
β-lactam antibiotics such as cephalexin, dicloxacillin, penicillin, or amoxicillin are first-line agents for typical cellulitis. 1, 2
MRSA is an uncommon cause of typical non-purulent cellulitis; a prospective study demonstrated that β-lactam therapy (cefazolin or oxacillin) was successful in 96% of patients, confirming that MRSA coverage is usually unnecessary. 1
Two high-quality randomized controlled trials found that adding trimethoprim-sulfamethoxazole (TMP-SMX) to cephalexin provided no additional benefit over cephalexin alone for uncomplicated cellulitis, reinforcing that MRSA-directed therapy is not needed in this setting. 3, 4
Recommended Dosing & Duration
Cephalexin 500 mg orally four times daily is the standard dose. 2, 5
Five days of therapy is sufficient for most patients if clinical improvement occurs by day 5; extending treatment offers no additional benefit. 1, 2
Patients should be reassessed at 48–72 hours to confirm clinical response (reduction in erythema, swelling, tenderness). 2
When to Add MRSA Coverage
Do not initiate MRSA-active antibiotics unless one or more of the following high-risk features are present:
- Lack of clinical response after 48–72 hours of β-lactam therapy. 1, 2
- Purulent drainage or exudate (purulent cellulitis phenotype). 6, 1, 2
- Penetrating trauma (especially injection drug use) or documented MRSA colonization. 1, 2
- Systemic toxicity (fever, hypotension, altered mental status, SIRS criteria). 6, 2
If MRSA coverage becomes necessary, oral options include:
- Clindamycin 300–450 mg three times daily (covers both MRSA and streptococci). 6, 2
- TMP-SMX 1–2 double-strength tablets twice daily (MRSA only; must add amoxicillin or cephalexin for streptococcal coverage). 6, 2
- Doxycycline 100 mg twice daily (MRSA only; must add a β-lactam for streptococcal coverage). 6, 2
Special Considerations for Hand Cellulitis
Hand infections are listed as an area "difficult to drain" in the IDSA guidelines, which is relevant for abscesses but does not change the antibiotic choice for uncomplicated cellulitis. 6
Elevation of the affected hand hastens improvement by promoting gravity drainage of edema and inflammatory mediators. 1
Surgical consultation should be considered if there is concern for deep space infection, flexor tenosynovitis, or necrotizing fasciitis—none of which are typical uncomplicated cellulitis. 6
Common Pitfalls to Avoid
Do not routinely order blood cultures or imaging for typical outpatient cellulitis; these are reserved for patients with severe systemic features, immunosuppression, or unusual exposures (e.g., immersion injury, animal bites). 1
Do not prescribe TMP-SMX or doxycycline as monotherapy for non-purulent cellulitis; these agents lack reliable streptococcal activity and require combination with a β-lactam if dual coverage is desired. 6, 1, 2
Do not add rifampin as adjunctive therapy; it provides no benefit and promotes resistance. 6, 2
Avoid overtreatment with prolonged courses; extending therapy beyond 5 days in a responding patient does not improve outcomes. 1, 2
FDA-Approved Indications & Safety
Cephalexin is FDA-approved for skin and skin structure infections caused by Staphylococcus aureus and/or Streptococcus pyogenes. 5
Caution in renal impairment: Dose adjustment may be required in patients with markedly impaired renal function. 5
Drug interaction with metformin: Cephalexin can increase metformin levels by ~34%; monitor glucose and adjust metformin dose if needed. 5
Pregnancy category B: Safe in pregnancy; however, cephalexin is excreted in breast milk (peak 4 mcg/mL at 4 hours), so caution is advised in nursing mothers. 5