In a patient with cellulitis of the right ear and cheek who is allergic to metronidazole, is Bactrim DS (trimethoprim‑sulfamethoxazole double strength) an appropriate monotherapy?

Bactrim DS Alone is Insufficient for Cellulitis of the Ear and Cheek

Bactrim DS (trimethoprim-sulfamethoxazole) should NOT be used as monotherapy for cellulitis of the right ear and cheek, even with a metronidazole allergy, because it lacks reliable activity against β-hemolytic streptococci, which are the primary pathogens in nonpurulent cellulitis. 1

Why Bactrim DS Monotherapy Fails

The fundamental problem is microbiological coverage:

• β-hemolytic streptococci (particularly Group A Streptococcus) are the predominant cause of typical cellulitis affecting the face, ear, and cheek 1
• Trimethoprim-sulfamethoxazole has intrinsic resistance issues with Group A Streptococcus and should not be used as a single agent for cellulitis when streptococcal infection is possible 2
• The Infectious Diseases Society of America explicitly recommends beta-lactam antibiotics as first-line treatment for nonpurulent cellulitis to target these streptococcal pathogens 1

When Bactrim DS Has a Role

Bactrim DS is appropriate for cellulitis only in specific circumstances:

• Purulent cellulitis with abscess formation, drainage, or exudate where MRSA is the likely pathogen 1
• After failure of beta-lactam therapy at 48-72 hours, suggesting MRSA involvement 1
• Penetrating trauma, injection drug use, or known MRSA colonization 1
• Must be combined with a beta-lactam if streptococcal coverage is still needed 1

Appropriate Treatment Options

For typical nonpurulent cellulitis of the ear and cheek:

First-line therapy:

• Cephalexin 500 mg PO four times daily (or other first-generation cephalosporin) 1
• Amoxicillin 500-875 mg PO twice daily for penicillin-tolerant patients 2
• Treatment duration: 5-6 days with close follow-up 1

For true penicillin/cephalosporin allergy:

• Clindamycin 300-450 mg PO three times daily provides both streptococcal and MRSA coverage 1, 3
• Doxycycline 100 mg PO twice daily is an alternative 1

Critical Dosing Considerations

If antibiotics with MRSA activity are needed:

• Weight-based dosing significantly impacts outcomes: inadequate dosing is independently associated with clinical failure (OR 2.01) 4
• Bactrim DS: 1-2 double-strength tablets twice daily (equivalent to TMP 4-6 mg/kg/dose every 12 hours) 1, 4
• Clindamycin: minimum 10 mg/kg/day divided into doses 4

Common Pitfalls to Avoid

• Do not assume all cellulitis requires MRSA coverage: nonpurulent cellulitis without risk factors should receive beta-lactams first 1
• The metronidazole allergy is irrelevant here: metronidazole has no role in routine cellulitis treatment and does not influence antibiotic selection 1
• Facial cellulitis can have serious complications: inadequate streptococcal coverage risks progression to deeper tissue infection 1
• Reassess at 48-72 hours: if the patient fails to improve on beta-lactam therapy, then add MRSA coverage 1