Can Bactrim Treat Cellulitis?
Bactrim (trimethoprim-sulfamethoxazole) should NOT be used as monotherapy for typical nonpurulent cellulitis, but it can be used in combination with a beta-lactam for purulent cellulitis or when MRSA coverage is specifically indicated. 1, 2
Standard Treatment for Typical Cellulitis
- Beta-lactam monotherapy is the standard of care for uncomplicated nonpurulent cellulitis, with a 96% success rate, because β-hemolytic streptococci—not MRSA—are the predominant pathogens. 1
- Recommended oral beta-lactams include cephalexin, dicloxacillin, amoxicillin, or penicillin for 5 days if clinical improvement occurs. 1
- Adding Bactrim to cephalexin provides no additional benefit in pure cellulitis without abscess, ulcer, or purulent drainage. 1, 3, 4
When Bactrim IS Appropriate
Bactrim should be added to beta-lactam therapy (not used alone) when specific MRSA risk factors are present: 1, 2
- Purulent drainage or exudate 1, 2
- Penetrating trauma or injection drug use 1, 2
- Known MRSA colonization 2
- Failure of beta-lactam therapy after 48-72 hours 2
- Systemic toxicity or SIRS 2
Dosing when indicated: 2
- Adults: 1-2 double-strength tablets (160/800 mg) orally twice daily 2
- Pediatrics: Trimethoprim 4-6 mg/kg/dose orally every 12 hours 2
- Duration: 5 days if clinical improvement occurs 1
Critical Evidence and Pitfalls
- Two high-quality randomized controlled trials (2013 and 2017) definitively showed that adding Bactrim to cephalexin for uncomplicated cellulitis provides no benefit over cephalexin alone. 3, 4
- The 2017 JAMA trial found clinical cure in 83.5% with cephalexin plus Bactrim versus 85.5% with cephalexin alone (no significant difference). 3
- Bactrim lacks reliable activity against β-hemolytic streptococci, which are the primary pathogens in typical cellulitis—this is why it cannot be used as monotherapy. 1
- In MRSA-prevalent areas (Hawaii study with 62% MRSA prevalence), Bactrim monotherapy achieved 91% success versus 74% for cephalexin, but this was in a mixed population that likely included purulent infections. 5
Contraindications
- Pregnancy (category C/D, especially third trimester) 2
- Children under 2 months of age 2
- Sulfonamide allergy 1
Alternative MRSA Coverage Options
If MRSA coverage is needed and Bactrim cannot be used: 1, 2
- Clindamycin 300-450 mg orally three times daily (covers both streptococci and MRSA as monotherapy) 1, 2
- Doxycycline 100 mg orally twice daily PLUS a beta-lactam (doxycycline alone is inadequate for streptococci) 1, 2
Bottom Line Algorithm
- Typical nonpurulent cellulitis: Use beta-lactam monotherapy (cephalexin, dicloxacillin, amoxicillin)—do NOT add Bactrim 1, 3, 4
- Purulent cellulitis or MRSA risk factors present: Use Bactrim PLUS a beta-lactam, or use clindamycin monotherapy 1, 2
- Never use Bactrim as monotherapy for any cellulitis due to inadequate streptococcal coverage 1