Bactrim (Trimethoprim-Sulfamethoxazole) Dosing for Abscess Treatment
For treatment of skin abscesses, the recommended dosage of Bactrim (trimethoprim-sulfamethoxazole) is 1-2 double-strength tablets (800mg/160mg) twice daily for 7-10 days in adults. 1
Adult Dosing
- Standard adult dose: 1-2 double-strength tablets (800mg/160mg) twice daily
- Duration: 7-10 days
- For simple abscesses: Consider shorter course (7 days)
- For complicated abscesses: Full 10-day course recommended
Pediatric Dosing
- Trimethoprim 4-6 mg/kg/dose
- Sulfamethoxazole 20-30 mg/kg/dose
- Administered every 12 hours
- Duration: 7-10 days
- Not recommended for children < 2 months of age 1
Clinical Decision Algorithm
Step 1: Determine if antibiotics are needed
- Simple, small abscess (<5 cm) with adequate drainage: Incision and drainage alone may be sufficient
- Indications for adding antibiotics 1:
- Abscess >5 cm
- Extensive or multiple sites of infection
- Rapid progression with associated cellulitis
- Systemic illness signs/symptoms
- Immunosuppression or comorbidities
- Extremes of age
- Difficult-to-drain locations (face, hand, genitalia)
- Associated septic phlebitis
- Lack of response to drainage alone
Step 2: Antibiotic selection
- First-line for suspected MRSA: Trimethoprim-sulfamethoxazole
- Alternative options:
- Clindamycin (300-450 mg PO TID)
- Doxycycline (100 mg PO BID)
- Linezolid (600 mg PO BID) - more expensive
Step 3: Monitoring and follow-up
- Evaluate clinical response within 48-72 hours
- Consider culture results if available
- Complete prescribed course even if symptoms improve quickly
Evidence Supporting TMP-SMX Use
Recent research strongly supports the use of TMP-SMX for abscess treatment. A placebo-controlled trial demonstrated that TMP-SMX in conjunction with incision and drainage significantly improved cure rates compared to drainage alone (81.7% vs 68.9%, p<0.001) 2. Another study showed TMP-SMX resulted in higher cure rates than placebo (80.5% vs 73.6%, p=0.005) and reduced subsequent surgical drainage procedures (3.4% vs 8.6%) 3.
Important Considerations and Contraindications
- Pregnancy: Not recommended in third trimester due to risk of hemolytic anemia in newborns 1
- Renal impairment: Dose adjustment may be needed
- Common side effects: Gastrointestinal disturbances (mild in most cases) 3
- Serious adverse reactions: Hypersensitivity reactions (rare) 2
- Drug interactions: Monitor for interactions with warfarin, phenytoin, and methotrexate
Special Populations
- MRSA infections: TMP-SMX is particularly effective for MRSA abscesses, with evidence showing a full 10-day course is superior to shorter regimens for preventing recurrence 4
- Immunocompromised patients: Consider longer duration of therapy and close follow-up
- Recurrent abscesses: Consider 5-day decolonization regimen with intranasal mupirocin, daily chlorhexidine washes, and decontamination of personal items 1
TMP-SMX has emerged as a preferred treatment for skin abscesses in the era of community-acquired MRSA, with strong evidence supporting its efficacy when combined with appropriate surgical drainage.