What is the recommended dosage of Bactrim (trimethoprim/sulfamethoxazole) for a patient with a Methicillin-resistant Staphylococcus aureus (MRSA) wound infection and normal renal function?

Bactrim Dosage for MRSA Wound Infection

For MRSA wound infections in adults with normal renal function, use trimethoprim-sulfamethoxazole (TMP-SMX) 1-2 double-strength tablets (160/800 mg) twice daily for 7-14 days, with the higher dose (2 DS tablets = 320/1600 mg twice daily) preferred for more extensive or severe infections. 1

Adult Dosing Recommendations

Standard dosing for purulent cellulitis or uncomplicated MRSA wound infections:

• 1-2 double-strength (DS) tablets orally twice daily 1
• Each DS tablet contains 160 mg trimethoprim and 800 mg sulfamethoxazole 1
• The higher dose (2 DS tablets = 320/1600 mg BID) is recommended for more serious infections 2

Treatment duration:

• 7-14 days depending on infection severity and clinical response 1, 3
• Simple infections may require only 5-10 days 3
• More complicated infections warrant the full 14-day course 1, 3

Pediatric Dosing

For children, dose based on the trimethoprim component:

• Trimethoprim 4-6 mg/kg/dose, sulfamethoxazole 20-30 mg/kg/dose orally every 12 hours 1
• Contraindicated in children under 2 months of age 1

Evidence Quality and Context

The IDSA guidelines provide Level AII evidence supporting TMP-SMX for MRSA skin and soft tissue infections 1. Research comparing standard dose (160/800 mg BID) versus high dose (320/1600 mg BID) found similar clinical resolution rates (75% vs 73%), suggesting either dose is effective, though guidelines favor the higher dose for serious infections 4. A randomized trial demonstrated TMP-SMX achieved 91.9% cure rates for uncomplicated wound infections, comparable to clindamycin 5.

Critical Caveats and Pitfalls

Streptococcal coverage limitation:

• TMP-SMX has poor activity against beta-hemolytic streptococci 1
• If streptococcal coverage is needed (non-purulent cellulitis), combine with a beta-lactam (amoxicillin or cephalexin) or use clindamycin instead 1, 3

When antibiotics are actually needed:

• For simple abscesses, incision and drainage alone may be adequate without antibiotics 1, 3
• Add antibiotics if: severe/extensive disease, rapid progression, systemic illness signs, comorbidities/immunosuppression, extremes of age, difficult-to-drain locations, septic phlebitis, or failure of drainage alone 1, 3

Pregnancy and allergy considerations:

• Pregnancy category C/D - not recommended in third trimester 1
• Contraindicated in sulfa allergy 2

Monitoring Requirements

• Monitor renal function with prolonged therapy 2
• Watch for hypersensitivity reactions 2
• Assess clinical response at 7-14 days to determine if treatment extension is needed 1

Alternative Agents When TMP-SMX Cannot Be Used

If TMP-SMX is contraindicated or ineffective:

• Clindamycin 300-450 mg orally three times daily (covers both MRSA and streptococci) 1, 3
• Doxycycline 100 mg orally twice daily (contraindicated under age 8) 1
• Linezolid 600 mg orally twice daily (expensive but highly effective) 1