Cephalexin Suspension Dosing for Skin Abscess
For a skin abscess, incision and drainage is the primary treatment; cephalexin suspension is indicated only as adjunctive therapy when specific risk factors are present.
Primary Treatment Principle
- Incision and drainage (I&D) alone is definitive therapy for simple abscesses without surrounding cellulitis—routine antibiotics are unnecessary after adequate surgical drainage 1.
- A randomized trial of 166 patients with skin abscesses showed a 90.5% cure rate with I&D plus placebo versus 84.1% with I&D plus cephalexin, demonstrating that antibiotics may be unnecessary after drainage of uncomplicated abscesses 2.
When to Add Cephalexin After Drainage
Add systemic antibiotics (including cephalexin suspension) only when any of the following risk factors are present 1:
- Multiple infection sites
- Systemic inflammatory response (fever >38°C, tachycardia, hypotension)
- Comorbidities or immunosuppression (diabetes, HIV/AIDS, malignancy)
- Extremes of age
- Abscesses in difficult-to-drain locations (face, hand, genitalia)
- Lack of clinical response to drainage alone
- Rapidly progressive or extensive disease
Pediatric Dosing (Oral Suspension)
- For mild-to-moderate infections: 25–50 mg/kg/day divided into 4 doses (every 6 hours) 3, 4.
- For MSSA infections requiring higher coverage: 75–100 mg/kg/day divided into 3–4 doses 3, 4.
- The liquid suspension formulation makes cephalexin practical for pediatric administration 3.
Adult Dosing (If Suspension Used)
- Standard dose: 500 mg orally every 6 hours (four times daily) 3, 4.
- For mild infections: 250 mg every 6 hours may be considered, though 500 mg is preferred for optimal tissue penetration 3.
Treatment Duration
- Treat for 5 days if clinical improvement occurs (reduced warmth, tenderness, erythema; absence of fever); extend only if symptoms have not improved 1, 4.
- High-quality evidence shows 5-day courses are as effective as 10-day courses for uncomplicated skin infections 4.
Critical Limitation: MRSA Coverage
- Cephalexin does NOT cover MRSA—it is completely ineffective against methicillin-resistant Staphylococcus aureus 3, 4.
- In the randomized trial, 87.8% of abscess isolates were MRSA, yet clinical cure rates were similar with placebo versus cephalexin, suggesting drainage is more important than antibiotic choice 2.
- If MRSA is suspected or confirmed, switch to MRSA-active agents 1, 3:
- Trimethoprim-sulfamethoxazole: 1–2 double-strength tablets twice daily (adults); 4–6 mg/kg/dose twice daily (children)
- Clindamycin: 300–450 mg every 6 hours (adults); 10–13 mg/kg/dose every 6–8 hours (children)
- Doxycycline: 100 mg twice daily (adults ≥8 years only; contraindicated in younger children)
When Cephalexin Is Appropriate
- Non-purulent cellulitis surrounding the abscess without MRSA risk factors 4.
- Methicillin-susceptible Staphylococcus aureus (MSSA) or streptococcal infections confirmed by culture 3, 4.
- Patients without penetrating trauma, injection drug use, known MRSA colonization, or systemic toxicity 4.
Common Pitfalls to Avoid
- Do not prescribe cephalexin for simple abscesses that can be adequately drained—antibiotics provide no additional benefit in most cases 1, 2.
- Do not use cephalexin for purulent cellulitis or abscesses when MRSA is likely—it lacks activity against this pathogen 1, 3, 4.
- Do not extend treatment to 7–10 days automatically—stop at 5 days if clinical improvement is evident 4.
- Do not use cephalexin in patients with severe penicillin allergy (anaphylaxis, angioedema, urticaria) due to cross-reactivity risk 5, 3.