What is the recommended dosing of cephalexin oral suspension for an adult with cellulitis?

Cephalexin Liquid Dosing for Adult Cellulitis

For adults with cellulitis, cephalexin oral suspension should be dosed at 500 mg four times daily (every 6 hours) for uncomplicated cases, with treatment duration of 5 days minimum, extended if infection has not improved. 12

Standard Dosing Regimen

The FDA-approved dosing for cephalexin in adults ranges from 1-4 grams daily in divided doses 1. For skin and soft tissue infections specifically:

• Standard dose: 500 mg every 6 hours (four times daily) 1
• Alternative: 500 mg every 12 hours (twice daily) is FDA-approved for uncomplicated skin infections 1
• Duration: Minimum 5 days, but extend if no improvement 2

Evidence for Higher Dosing

Recent research suggests higher doses may be beneficial for moderate-to-severe cellulitis:

• A 2023 pilot RCT found that 1000 mg four times daily had lower treatment failure rates (3.2%) compared to standard 500 mg dosing (12.9%), though with more minor adverse effects 3
• Pharmacokinetic/pharmacodynamic studies indicate higher doses optimize target attainment, especially for Staphylococcus aureus in moderate-severe infections 4

For moderate-to-severe cellulitis or patients at higher risk of treatment failure, consider 1000 mg four times daily rather than the standard 500 mg dose.

Clinical Decision Algorithm

Mild cellulitis (no systemic signs, limited erythema):

• 500 mg every 12 hours OR 500 mg every 6 hours 1
• Outpatient management 2

Moderate cellulitis (larger area, more symptoms but no SIRS):

• 500-1000 mg every 6 hours 13
• Consider higher dose if obesity, diabetes, or immunocompromise

Severe cellulitis (SIRS present, extensive involvement):

• Consider IV therapy or 1000 mg every 6 hours if oral route chosen 23
• May require hospitalization 2

Important Caveats

MRSA coverage: Cephalexin alone is NOT active against MRSA. Add trimethoprim-sulfamethoxazole if the patient has 2:

• Penetrating trauma
• Evidence of MRSA elsewhere
• Nasal MRSA colonization
• Injection drug use
• Systemic inflammatory response

However, a large 2017 RCT found that adding trimethoprim-sulfamethoxazole to cephalexin did not significantly improve cure rates for uncomplicated cellulitis (83.5% vs 85.5%) 5, suggesting streptococci remain the primary pathogen in most non-purulent cellulitis cases.

Preparation of Liquid Suspension

For the 250 mg/5 mL concentration:

• Add 71 mL water to 100 mL bottle OR 140 mL water to 200 mL bottle
• Add water in two portions, shaking well after each
• Store in refrigerator; stable for 14 days 1

Adult dosing with 250 mg/5 mL suspension: 10 mL (2 teaspoons) every 6 hours for standard 500 mg dose, or 20 mL (4 teaspoons) every 6 hours for 1000 mg dose.

Adjunctive Measures

Beyond antibiotics, the IDSA guidelines strongly recommend 2:

• Elevation of affected extremity
• Treatment of predisposing factors (edema, venous insufficiency, obesity)
• Examination of interdigital toe spaces for tinea pedis, as treating toe web maceration reduces recurrence risk