Bactrim Dosage for Children
Standard Treatment Dosing
For most infections in children over 2 months of age, administer Bactrim at 8-12 mg/kg/day of the trimethoprim component and 40-60 mg/kg/day of sulfamethoxazole, divided into 2 doses given every 12 hours. 1, 2
Age-Based Restrictions
Weight-Based Dosing Table (Every 12 Hours)
The following provides practical dosing guidance 2:
- 10 kg (22 lbs): 1 single-strength tablet (400mg/80mg)
- 20 kg (44 lbs): 2 single-strength tablets OR 1 double-strength tablet
- 30 kg (66 lbs): 1½ double-strength tablets
- 40 kg (88 lbs): 2 double-strength tablets
Indication-Specific Dosing
Urinary Tract Infections & Acute Otitis Media
- Dose: 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, divided every 12 hours 2
- Duration: 10 days for UTI; 10 days for otitis media 2
Shigellosis
- Dose: Same as above (40/8 mg/kg/day divided every 12 hours) 2
- Duration: 5 days 2, 3
- Research demonstrates this regimen achieves clinical response within 1.7 days on average, with stool cultures clearing within 1.6 days 3
Skin and Soft Tissue Infections (including MRSA)
- Dose: 8-12 mg/kg/day of trimethoprim component 1
- Duration: 7-10 days 1
- For severe MRSA osteomyelitis, the Taiwanese guidelines recommend 4 mg/kg/dose of trimethoprim every 8-12 hours, typically combined with rifampin for >6 weeks 4
Pneumocystis jirovecii Pneumonia (PCP)
Treatment:
- Dose: 75-100 mg/kg/day sulfamethoxazole and 15-20 mg/kg/day trimethoprim, divided into 4 doses every 6 hours 2
- Duration: 14-21 days 2
Prophylaxis:
- Dose: 750 mg/m²/day sulfamethoxazole with 150 mg/m²/day trimethoprim, divided into 2 doses 2
- Schedule: Given on 3 consecutive days per week (alternative to daily dosing) 5, 2
- Maximum daily dose: Do not exceed 1600 mg sulfamethoxazole and 320 mg trimethoprim 2
- For a 16 kg child, this equals approximately 128 mg trimethoprim per day 5
Pharmacokinetic Considerations
Age-Related Dosing Adjustments
- Higher weight-based doses are required in younger children to achieve equivalent drug exposure compared to adults 6
- The standard 8/40 mg/kg/day divided every 12 hours matches adult exposure and achieves therapeutic targets for bacteria with MIC ≤0.5 mg/L in >90% of children 6
- For bacteria with MIC up to 1 mg/L, higher doses may be needed: 12/60 mg/kg/day for ages 6-21 years, or 15/75 mg/kg/day for ages 0-6 years 6
Renal Impairment
Dosing must be adjusted based on creatinine clearance 2:
- CrCl >30 mL/min: Standard dosing
- CrCl 15-30 mL/min: Reduce dose by 50%
- CrCl <15 mL/min: Use not recommended 2
For IV administration in renal failure, increase the dosing interval (in hours) to 12 times the serum creatinine level in mg/dL, with a maximum interval of 48 hours 7
Monitoring Requirements
Hematologic Surveillance
- Obtain complete blood count with differential and platelet count at treatment initiation 5
- Repeat monthly during prolonged therapy to assess for hematologic toxicity 5
- Thrombocytopenia risk increases with higher serum trimethoprim levels and longer treatment duration 7
Important Safety Considerations
Contraindications
Use with Caution
- G6PD deficiency: Risk of hemolytic anemia 1
- Renal insufficiency: Requires dose adjustment 1
- Hepatic insufficiency: Monitor closely 1
Drug Interactions
- Methotrexate: May increase toxicity 1
- Warfarin and other anticoagulants: Enhanced anticoagulant effect 1
- Oral hypoglycemics: Increased hypoglycemia risk 1
Common Adverse Effects
- Rash, gastrointestinal disturbances, and hematologic abnormalities are most common 5
- If life-threatening toxicity occurs, permanently discontinue the drug 5