Bactrim DS Dosing for Melioidosis
For the eradication phase of melioidosis, administer TMP-SMX double-strength tablets (160 mg trimethoprim/800 mg sulfamethoxazole) twice daily for 12-20 weeks following completion of the intensive intravenous phase. 1, 2
Weight-Based Dosing Recommendations
The standard adult dosing regimen is:
- <40 kg: 160/800 mg (1 DS tablet) twice daily 3
- 40-60 kg: 240/1200 mg (1.5 DS tablets) twice daily 3
- >60 kg: 320/1600 mg (2 DS tablets) twice daily 3
Add folic acid 0.1 mg/kg up to 5 mg daily to prevent antifolate effects without compromising antimicrobial activity. 3
Treatment Duration: Critical Decision Point
The optimal duration is 12 weeks rather than 20 weeks. 4 A 2021 randomized controlled trial demonstrated that 12 weeks of TMP-SMX resulted in significantly lower all-cause mortality (0.3% vs 3%) compared to 20 weeks, while maintaining noninferiority for the composite endpoint of recurrence and mortality. 4 This contradicts older Thai guidelines recommending 20 weeks, but the mortality benefit makes 12 weeks the evidence-based choice. 5, 4
Monotherapy vs Combination Therapy
Use TMP-SMX monotherapy—do not add doxycycline. 5 A 2014 multicenter trial of 626 patients demonstrated that TMP-SMX alone was noninferior to TMP-SMX plus doxycycline for preventing recurrence (5% vs 7% recurrence rates), with significantly fewer adverse reactions (39% vs 53%). 5 This supersedes older recommendations for combination therapy. 6
Special Populations and Alternatives
For patients who cannot tolerate TMP-SMX:
- Pregnant women: Amoxicillin-clavulanate 20/5 mg/kg every 8 hours (maximum 1500/375 mg every 8 hours), though this is significantly less effective 3, 1
- Children: Same weight-based TMP-SMX dosing as adults 3
- Sulfa allergy: Amoxicillin-clavulanate or doxycycline 100 mg twice daily 1, 7
Extended Duration Indications
Extend treatment to 4-8 weeks or longer (beyond the standard 12 weeks) for:
- Central nervous system involvement (add TMP-SMX 8/40 mg/kg IV/PO every 12 hours up to 320/1600 mg) 3
- Osteomyelitis or septic arthritis 3, 1
- Deep-seated abscesses or organ collections 1, 2
- Extensive pulmonary disease 1, 2
- Critical illness at presentation 1, 2
Critical Pitfalls to Avoid
Do not use these antibiotics—they are associated with treatment failure or higher mortality:
- Ertapenem, azithromycin, moxifloxacin (inherent resistance) 3, 1
- Ceftriaxone or cefotaxime (higher mortality than ceftazidime) 1
- Amoxicillin-clavulanate as prophylaxis (ineffective in animal models) 7
- First- or second-generation cephalosporins, penicillin, ampicillin, gentamicin, streptomycin, polymyxin (inherent resistance) 1, 2
Integration with Intensive Phase
The eradication phase follows at least 14 days of intravenous therapy with meropenem (preferred), imipenem, or ceftazidime. 1, 2 Meropenem demonstrates superior clinical outcomes compared to ceftazidime in severe disease. 1 For melioidosis-induced septic shock, consider adding G-CSF 300 mg IV for 10 days during the intensive phase. 3, 7
Post-Exposure Prophylaxis Context
If prescribing TMP-SMX for post-exposure prophylaxis (bioterrorism or high-risk exposure), administer within 24 hours of exposure—this achieved 100% survival in animal models. 7 Pre-exposure prophylaxis with TMP-SMX showed 100% survival rates versus 80% with doxycycline. 7