What is the recommended dose of Bactrim (trimethoprim/sulfamethoxazole) for an adult patient with normal renal function and cellulitis?

Bactrim Dosing for Cellulitis

For adults with normal renal function and cellulitis, prescribe Bactrim DS (trimethoprim 160 mg/sulfamethoxazole 800 mg) one double-strength tablet orally twice daily for 7-10 days. 1, 2

Standard Dosing Regimen

• The recommended dose is 1 double-strength tablet (160 mg trimethoprim/800 mg sulfamethoxazole) orally twice daily for 7-10 days for skin and soft tissue infections including cellulitis 1, 2
• This dosing applies specifically to purulent cellulitis and infections where Staphylococcus aureus, including community-acquired MRSA, is suspected 1

Weight-Based Dosing Considerations

Inadequate dosing significantly increases treatment failure rates. 3

• Weight-based dosing of at least 5 mg/kg/day of the trimethoprim component is critical for optimal outcomes 3
• Patients receiving inadequate doses (<5 mg TMP/kg/day) had a 30% clinical failure rate compared to 17% in those receiving adequate doses (p=0.032) 3
• Inadequate dosing was independently associated with clinical failure (OR=2.01, p=0.032) in hospitalized cellulitis patients 3
• For heavier patients, consider 2 double-strength tablets twice daily to achieve adequate weight-based dosing 3

Monitoring and Expected Response

• Clinical improvement should be evident within 48-72 hours of initiating therapy 1, 2
• If no improvement occurs within this timeframe, consider possible Bactrim resistance or need for incision and drainage if abscess formation has developed 1
• Complete the full 7-10 day course even if symptoms improve rapidly 1

Important Caveats and Contraindications

• Bactrim is contraindicated in pregnant women in the third trimester 1, 2
• Contraindicated in infants <2 months, breastfeeding women, and patients with hypersensitivity to sulfonamides or trimethoprim 2
• Use with caution in patients with liver or kidney dysfunction, folate deficiency, blood dyscrasias, and elderly patients 2
• Common adverse effects include rash, urticaria, nausea, vomiting, and gastrointestinal disturbances 1
• Rare but serious adverse effects include Stevens-Johnson syndrome and agranulocytosis 1, 4

Alternative Antibiotics if Bactrim Cannot Be Used

• Clindamycin 300-450 mg orally three times daily 1
• Doxycycline 100 mg orally twice daily 1
• Linezolid 600 mg orally twice daily 1

Clinical Context

• One trial comparing cephalexin plus trimethoprim-sulfamethoxazole versus cephalexin alone for uncomplicated cellulitis showed no significant difference in clinical cure rates in the per-protocol analysis (83.5% vs 85.5%, p=0.50), though the modified intention-to-treat analysis suggested possible benefit that warrants further research 5
• Incision and drainage should be performed if fluctuance is present, but antimicrobial therapy with Bactrim is still recommended for surrounding cellulitis 1