Keflex Dosing for Cellulitis
For an adult with uncomplicated cellulitis of the hand and normal renal function, prescribe cephalexin 500 mg orally every 6 hours (four times daily) for 5-7 days. 1, 2
Standard Dosing Regimen
The FDA-approved dosing for skin and soft tissue infections allows flexibility, but the evidence supports specific approaches:
- Standard dose: 500 mg every 6 hours (QID) is the established regimen for uncomplicated cellulitis 2
- Alternative dosing: 500 mg every 12 hours (BID) may be used for uncomplicated cases, though QID dosing remains standard 2
- Duration: 5 days is as effective as 10 days if clinical improvement occurs by day 5 1
Key Clinical Considerations
MRSA Coverage is Usually Unnecessary
β-lactam monotherapy with cephalexin alone is recommended for typical cellulitis without purulent drainage. 1
- MRSA is an uncommon cause of non-purulent cellulitis, with β-lactams successful in 96% of cases 1
- A high-quality double-blind RCT demonstrated that cephalexin plus trimethoprim-sulfamethoxazole was no more effective than cephalexin alone for pure cellulitis (83.5% vs 85.5% cure rates) 3
- Add MRSA coverage only if: penetrating trauma (especially IV drug use), purulent drainage, or concurrent MRSA infection elsewhere 1
Dosing Nuances
Recent research suggests potential benefits of higher dosing, though not yet standard of care:
- A 2023 pilot RCT comparing 1000 mg QID versus 500 mg QID showed lower treatment failure with high-dose (3.2% vs 12.9%), but with more minor adverse effects 4
- The FDA label permits up to 4 grams daily in divided doses for more severe infections 2
- For typical uncomplicated hand cellulitis, stick with 500 mg QID unless clinical severity warrants escalation 2
Treatment Duration Algorithm
- Day 3-5: Assess clinical response by phone or in-person 1
- If improving by day 5: Complete 5-day course 1
- If not improving by day 3-4: Consider treatment failure (persistent fever, increased erythema >25%, or increased swelling/tenderness) and reassess for abscess, MRSA, or need for IV therapy 1
- If minimal improvement but progressing: Extend to 7-10 days 1, 2
Common Pitfalls to Avoid
- Don't routinely add MRSA coverage: The evidence shows no benefit for non-purulent cellulitis, and combination therapy increases adverse effects without improving outcomes 3
- Don't automatically prescribe 10 days: This leads to unnecessary antibiotic exposure when 5 days suffices with clinical improvement 1
- Don't miss an abscess: Consider ultrasound if uncertain, as purulent collections require drainage, not just antibiotics 1
- Don't forget adjunctive measures: Elevation of the affected hand hastens improvement by promoting drainage of edema 1
Practical Prescribing
For a typical adult with hand cellulitis:
- Prescription: Cephalexin 500 mg capsules, take 1 capsule by mouth four times daily for 5-7 days 2
- Counsel patient: Expect improvement within 48-72 hours; return if worsening fever, spreading redness, or no improvement by day 3-5 1
- Follow-up: Phone check at days 3-5, with in-person visit only if not improving 1