Bactrim Dosing for a 27 kg Pediatric Patient
For a 27 kg child, administer Bactrim at 8-12 mg/kg/day of trimethoprim (216-324 mg/day) divided into two doses every 12 hours, which translates to approximately 108-162 mg of trimethoprim per dose. 1, 2
Standard Treatment Dosing
The recommended dose is 8-12 mg/kg/day of trimethoprim and 40-60 mg/kg/day of sulfamethoxazole, divided every 12 hours for most infections. 1, 2
For a 27 kg child, this calculates to:
Using standard tablet formulations, this typically means 1 double-strength tablet (160 mg trimethoprim/800 mg sulfamethoxazole) every 12 hours for most infections. 3
Indication-Specific Adjustments
For mild-to-moderate infections (urinary tract infections, skin/soft tissue infections): Use the lower end of the dosing range at 8-10 mg/kg/day of trimethoprim. 2
For serious infections (severe MRSA): Consider 10-12 mg/kg/day of trimethoprim, or up to 15-20 mg/kg/day divided every 6-8 hours for life-threatening infections. 2
For Pneumocystis jirovecii pneumonia treatment: Use 15-20 mg/kg/day of trimethoprim (75-100 mg/kg/day sulfamethoxazole) divided every 6 hours for 14-21 days. 3
Formulation Considerations
At 27 kg, either tablets or liquid formulation can be used, though liquid may provide more precise dosing flexibility. 2
The FDA-approved dosing table indicates that children weighing 44 lb (20 kg) receive 1 tablet (400 mg/80 mg) every 12 hours, while those at 66 lb (30 kg) receive 1½ tablets every 12 hours. 3
For a 27 kg child, 1 double-strength tablet every 12 hours is appropriate and falls within the recommended 8-12 mg/kg/day range. 3
Critical Safety Considerations
Bactrim is contraindicated in children under 2 months of age due to kernicterus risk. 1
Monitor complete blood count with differential and platelet count at treatment initiation and monthly during prolonged therapy to assess for hematologic toxicity (neutropenia, thrombocytopenia, anemia). 1, 2
Use with extreme caution in G6PD deficiency due to hemolytic anemia risk. 2
Adjust dosing in renal insufficiency: When creatinine clearance is 15-30 mL/min, use half the usual dose; avoid use when creatinine clearance is below 15 mL/min. 3
Common Pitfalls to Avoid
Do not confuse dosing based on trimethoprim versus sulfamethoxazole components—always dose based on the trimethoprim component (the 1:5 ratio is maintained automatically in fixed-dose combinations). 1, 2
Adverse reactions occur in approximately 15% of patients, with dermatologic reactions (rash), hematologic effects, and gastrointestinal complaints being most common. 1
For mild rash, temporarily discontinue and restart when resolved; for urticarial rash or Stevens-Johnson syndrome, permanently discontinue. 1