Cotrimoxazole (Trimethoprim/Sulfamethoxazole) Syrup Dosage and Treatment Duration
The recommended dosage for cotrimoxazole syrup is based on the trimethoprim component at 8 mg/kg/day and sulfamethoxazole 40 mg/kg/day in 2 divided doses, with treatment duration varying from 5-14 days depending on the infection type. 1
Pediatric Dosing
Children ≥2 months of age:
Urinary tract infections and acute otitis media:
- Trimethoprim 8 mg/kg/day + Sulfamethoxazole 40 mg/kg/day
- Divided into 2 doses (every 12 hours)
- Duration: 10 days 1
Shigellosis:
- Same dosage: Trimethoprim 8 mg/kg/day + Sulfamethoxazole 40 mg/kg/day
- Divided into 2 doses (every 12 hours)
- Duration: 5 days 1
Pneumocystis jirovecii pneumonia (PCP) treatment:
PCP prophylaxis in HIV-exposed/infected children:
- 750 mg/m²/day sulfamethoxazole with 150 mg/m²/day trimethoprim
- Given in 2 divided doses
- 3 consecutive days per week 1
Weight-based dosing guide for children:
| Weight (kg) | Weight (lb) | Dose every 12 hours |
|---|---|---|
| 10 | 22 | 1 tablet (80/400 mg) |
| 20 | 44 | 1 tablet (80/400 mg) |
| 30 | 66 | 1½ tablets (120/600 mg) |
| 40 | 88 | 2 tablets (160/800 mg) or 1 DS tablet |
Important Considerations
Contraindications:
- Not recommended for infants <2 months due to risk of kernicterus 2, 1
- Contraindicated during third trimester of pregnancy 2
- Contraindicated in patients with known hypersensitivity to trimethoprim or sulfonamides 2
Adverse Effects:
- Common: Gastrointestinal disturbances, rash
- Rare but serious: Stevens-Johnson syndrome, blood dyscrasias, hepatic necrosis 2
- If mild to moderate skin rash occurs, temporarily discontinue and consider rechallenge after resolution 2
Special Populations:
- Renal impairment: Dose adjustment required 1
- CrCl >30 mL/min: Standard regimen
- CrCl 15-30 mL/min: Half the usual regimen
- CrCl <15 mL/min: Not recommended
Specific Clinical Applications
MRSA Skin and Soft Tissue Infections:
- Adults: 1-2 double-strength tablets (160/800 mg) twice daily
- Duration: Variable, typically 7-14 days 2
Pertussis (Whooping Cough):
- Alternative when macrolides are contraindicated
- Same dosing: Trimethoprim 8 mg/kg/day + Sulfamethoxazole 40 mg/kg/day in 2 divided doses
- Duration: 14 days 2
Non-severe Pneumonia:
- May be used as an alternative to amoxicillin, though amoxicillin is generally preferred 2
- Standard pediatric dosing applies
Clinical Pearls
- For severe infections, monitor complete blood counts with differential and platelet count at initiation and monthly thereafter to assess for hematologic toxicity
- Ensure adequate hydration to prevent crystalluria and renal stones 2
- Drug interactions must be considered when used with methotrexate, oral anticoagulants, antidiabetic agents, and anticonvulsants 2
- Cotrimoxazole provides good coverage against many common respiratory pathogens, but its activity against beta-hemolytic streptococci is not well-defined 2
By following these dosing guidelines, clinicians can optimize the efficacy of cotrimoxazole syrup while minimizing the risk of adverse effects.