Bactrim DS Dosing for Bacterial Infections
Standard Dosing Regimens
For most common bacterial infections in adults, Bactrim DS (800-160 mg) is dosed as one tablet twice daily, with treatment duration varying from 5 to 14 days depending on the specific infection type. 1
Urinary Tract Infections (UTIs)
- Adults: 1 DS tablet every 12 hours for 10-14 days 1
- Pediatric patients (≥2 months): 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, divided every 12 hours for 10 days 1
- For uncomplicated cystitis, a 3-day course of 1 DS tablet twice daily is effective when the uropathogen is known to be susceptible 2
- Pyelonephritis: 1 DS tablet twice daily for 14 days if the organism is susceptible 2
Skin and Soft Tissue Infections (SSTI)
- MRSA infections: 1-2 DS tablets twice daily 2
- Methicillin-susceptible infections: 1-2 DS tablets twice daily 2
- Treatment duration is typically 7 days, adjusted based on clinical response 2
Gastrointestinal Infections
- Shigellosis: 1 DS tablet every 12 hours for 5 days 1
- Traveler's diarrhea: 1 DS tablet every 12 hours for 5 days 1
Respiratory Infections
- Acute exacerbations of chronic bronchitis: 1 DS tablet every 12 hours for 14 days 1
Pneumocystis jirovecii Pneumonia (PCP)
- Treatment: 75-100 mg/kg sulfamethoxazole and 15-20 mg/kg trimethoprim per 24 hours, divided every 6 hours for 14-21 days 1
- Prophylaxis: 1 DS tablet daily 2, 1
- Prophylaxis is indicated for patients with CD4+ T-cells <200/μL or constitutional symptoms 2
Renal Dose Adjustments
Dosing must be reduced in renal impairment to prevent toxicity: 1
- CrCl >30 mL/min: Standard dosing
- CrCl 15-30 mL/min: 50% of usual dose
- CrCl <15 mL/min: Use not recommended 1
Important Clinical Considerations
Efficacy Limitations
- Resistance patterns matter: Clinical cure rates drop significantly with resistant organisms (84% vs 41% for susceptible vs resistant strains in UTIs) 2
- For SSTI, efficacy is "poorly documented" compared to other agents 2
- Not recommended as first-line for pyelonephritis unless susceptibility is confirmed, and should be given with an initial long-acting parenteral agent (e.g., 1g ceftriaxone) if susceptibility is unknown 2
Common Pitfalls
- Do not use in children <2 months of age - this is an absolute contraindication 1
- Avoid in pregnancy - not recommended due to potential fetal harm 2
- Side effects occur in approximately 8-38% of patients, including rash, GI upset, and rarely serious reactions like Stevens-Johnson syndrome 2
- Hematologic monitoring may be warranted with prolonged use, particularly in elderly patients 3
Pharmacokinetic Considerations
- Steady-state concentrations are reached after 3 days of continuous dosing 3
- Elderly patients achieve 2-3 times higher plasma concentrations than younger adults, though standard dosing is typically maintained unless renal function is impaired 3
- Single-dose therapy (2 DS tablets once) has been studied for uncomplicated UTIs with 93% efficacy and significantly fewer side effects (4% vs 24%) compared to 10-day therapy 4