Recommended Dosage of Bactrim (Trimethoprim/Sulfamethoxazole)
The standard adult dosage of Bactrim is 1 double-strength tablet (containing 160mg trimethoprim and 800mg sulfamethoxazole) or 2 regular-strength tablets every 12 hours, with specific adjustments based on indication and renal function. 1, 2
Adult Dosing by Indication
Urinary Tract Infections
- 1 double-strength tablet (DS) or 2 regular tablets every 12 hours for 10-14 days 1
Acute Exacerbations of Chronic Bronchitis
- 1 double-strength tablet or 2 regular tablets every 12 hours for 14 days 1
Traveler's Diarrhea
- 1 double-strength tablet or 2 regular tablets every 12 hours for 5 days 1
Shigellosis
- 1 double-strength tablet or 2 regular tablets every 12 hours for 5 days 1
Pneumocystis Pneumonia
- Treatment: 75-100 mg/kg sulfamethoxazole and 15-20 mg/kg trimethoprim per 24 hours, divided into doses given every 6 hours for 14-21 days 1
- Prophylaxis: 1 double-strength tablet daily 1
MRSA Skin and Soft Tissue Infections
Pediatric Dosing
Children 2 months and older
- Urinary tract infections/Acute otitis media: 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, divided into two doses given every 12 hours for 10 days 1, 2
- Shigellosis: Same dosage as above but for 5 days 1
Weight-based dosing guide for children
- 10 kg (22 lb): 1 regular tablet every 12 hours
- 20 kg (44 lb): 1 regular tablet every 12 hours
- 30 kg (66 lb): 1½ regular tablets every 12 hours
- 40 kg (88 lb): 2 regular tablets or 1 DS tablet every 12 hours 1, 2
Renal Dose Adjustments
- Creatinine clearance >30 mL/min: Standard dosage
- Creatinine clearance 15-30 mL/min: Half the usual dosage
- Creatinine clearance <15 mL/min: Not recommended 1, 2
Important Considerations
Age Restrictions
- Contraindicated in infants less than 2 months of age 1, 2
- Not recommended during third trimester of pregnancy 3
Monitoring
- Complete blood counts with differential and platelet count should be performed at initiation and monthly for patients on long-term therapy 4
- Elderly patients may require dose adjustment due to higher peak concentrations and reduced clearance of trimethoprim 5
Common Side Effects
- Gastrointestinal disturbances
- Hypersensitivity skin reactions
- Rarely: Stevens-Johnson syndrome, blood dyscrasias, and hepatic necrosis 4
Pharmacokinetic Considerations
- Peak levels are higher and more reliable after IV than oral dosing 6
- In elderly patients, trimethoprim concentrations may be 2-3 times higher than in younger adults due to reduced renal clearance 5
By following these dosing guidelines and monitoring parameters, Bactrim can be used effectively for various infectious conditions while minimizing the risk of adverse effects.