Bactrim Dosing for Adult Skin and Soft Tissue Infections
For uncomplicated skin and soft tissue infections in adults, the standard dose of Bactrim (trimethoprim-sulfamethoxazole) is 1-2 double-strength tablets (800mg/160mg sulfamethoxazole/trimethoprim) twice daily by mouth for approximately 7 days. 1
Oral Dosing for Outpatient Management
- Standard dose: 1-2 double-strength tablets (160mg/800mg TMP/SMX) twice daily orally 2, 1
- Treatment duration is typically 7 days, adjusted based on clinical response 2, 1
- This dosing applies to purulent infections (abscesses, furuncles) where MRSA is suspected 1
Intravenous Dosing for Severe Infections
- For severe infections requiring hospitalization: 8-12 mg/kg/day (based on trimethoprim component) divided into 4 doses intravenously 2, 1
- This higher-intensity regimen is reserved for patients with systemic signs of infection or those unable to tolerate oral therapy 2
High-Dose Considerations
Research comparing standard (160/800mg) versus high-dose (320/1600mg) twice daily showed no significant difference in clinical resolution rates (73% vs 75%, p=0.79), suggesting the standard dose is adequate for most MRSA skin infections 3. Both doses achieved good tissue penetration and bactericidal activity against S. aureus and streptococci 4.
Critical Clinical Caveats
Bactrim has poor activity against beta-hemolytic streptococci, which are common pathogens in non-purulent cellulitis 1. For non-purulent cellulitis where streptococci are likely:
- Beta-lactams (such as cephalexin) are preferred first-line agents 2, 1
- If Bactrim is used, it must be combined with a beta-lactam for adequate streptococcal coverage 1
Bactrim is most appropriate for:
- Purulent infections (abscesses, furuncles) with suspected MRSA 2, 1
- Patients with documented MRSA on culture 1
- Patients who failed beta-lactam therapy 1
Important Safety Warnings
- Agranulocytosis is a rare but serious adverse effect, with documented cases occurring after 10 days of therapy 5
- Pregnancy category C/D—contraindicated in third trimester 1
- Avoid in patients with sulfa allergies 1
- For mixed aerobic-anaerobic infections, Bactrim requires combination with agents providing anaerobic coverage 1