What is the appropriate treatment for incision cellulitis with purulence using Keflex (cephalexin) and Bactrim (sulfamethoxazole/trimethoprim)?

Treatment of Incision Cellulitis with Purulence

For incision cellulitis with purulence, you should use BOTH Keflex (cephalexin) AND Bactrim (trimethoprim-sulfamethoxazole) together to cover both methicillin-resistant Staphylococcus aureus (MRSA) and beta-hemolytic streptococci. 1, 2

Rationale for Combination Therapy

Purulent cellulitis requires MRSA coverage, but incisional infections also need streptococcal coverage, making monotherapy with either agent inadequate. 1, 2

• Bactrim (TMP-SMX) provides excellent MRSA coverage but has poor activity against beta-hemolytic streptococci, which are common pathogens in surgical site infections 1, 2
• Cephalexin covers beta-hemolytic streptococci and methicillin-susceptible S. aureus (MSSA) but lacks activity against MRSA 1
• The combination covers the full spectrum of likely pathogens in incisional surgical site infections involving the trunk or extremities 1

Specific Dosing Recommendations

Adult dosing:

• Cephalexin 500 mg orally four times daily 1
• TMP-SMX 1-2 double-strength tablets (160mg/800mg) orally twice daily 1, 2

Pediatric dosing:

• Cephalexin 10-13 mg/kg/dose orally every 6-8 hours, not to exceed 40 mg/kg/day 1
• TMP-SMX: Trimethoprim 4-6 mg/kg/dose, sulfamethoxazole 20-30 mg/kg/dose orally every 12 hours 1

Duration: 7-10 days based on clinical response 1, 2

Critical Management Steps Beyond Antibiotics

Incision and drainage is mandatory if there is any purulent collection or abscess - antibiotics alone are insufficient 1, 3

• Obtain cultures from purulent drainage before starting antibiotics to guide definitive therapy and detect resistance patterns 1, 2
• Perform wound care with dressing changes as appropriate for the surgical site 1
• Monitor for treatment failure at 48-72 hours - worsening erythema, fever, or systemic signs require escalation to IV therapy 1

When to Consider Alternative Regimens

If the patient cannot tolerate TMP-SMX or cephalexin:

• Clindamycin 300-450 mg orally three times daily alone provides coverage for both MRSA and streptococci 1, 2
• Doxycycline 100 mg orally twice daily PLUS cephalexin is an alternative combination 1

Warning: Clindamycin monotherapy carries higher risk of C. difficile infection compared to other oral agents 1

Important Contraindications and Precautions

TMP-SMX is contraindicated in:

• Women in the third trimester of pregnancy (category C/D) 1, 2
• Children under 2 months of age 1, 2

Doxycycline should be avoided in:

• Children under 8 years of age 1
• Pregnant or lactating women 3

When to Escalate to IV Therapy

Admit for IV antibiotics if any of the following are present:

• Systemic toxicity (fever >38°C, tachycardia >90 bpm, tachypnea >24 breaths/min, abnormal WBC) 1
• Rapidly progressive infection despite oral antibiotics 1
• Immunocompromised state 1
• Inability to drain purulent collection completely 1
• Signs of deeper infection (bullae, skin sloughing, hypotension) 1

For severe infections requiring hospitalization, use vancomycin 15-20 mg/kg IV every 8-12 hours to ensure adequate MRSA coverage 1

Common Pitfalls to Avoid

Do not use Bactrim alone for incisional cellulitis - this is a critical error because streptococcal coverage will be inadequate, leading to treatment failure 2, 4

Do not use cephalexin alone if purulence is present - MRSA is the predominant pathogen in purulent infections and cephalexin lacks activity against it 1, 5, 6

Do not skip incision and drainage - multiple studies confirm that antibiotics without drainage of purulent collections leads to treatment failure 1, 3