What is the dose of Septran (co-trimoxazole) for PCP prophylaxis in a 10kg child with B-cell Acute Lymphoblastic Leukemia (B-ALL)?

Dosage of Co-trimoxazole (Septran) for PCP Prophylaxis in a 10kg Child with B-ALL

For a 10kg child with B-ALL, the recommended dose of co-trimoxazole (Septran) for PCP prophylaxis is 150 mg/m² of trimethoprim component per day (approximately 75-100 mg of trimethoprim for this child), given in divided doses twice daily for 3 consecutive days per week.

Dosing Calculation and Options

Weight-Based Dosing:

• For a 10kg child, the following options are available:

1. Standard regimen (preferred):

   • 150 mg/m²/day of trimethoprim component (with 750 mg/m²/day of sulfamethoxazole)
   • Given in two divided doses for 3 consecutive days per week 1
   • For a 10kg child (approximately 0.5 m² body surface area), this equals about 75 mg of trimethoprim daily on prophylaxis days

2. Alternative regimens:

   • Two non-consecutive days per week (twice daily dosing on each day) 2, 3
   • 2-3 mg/kg/day of trimethoprim component as a single daily dose 4
   • 5-6 mg/kg of trimethoprim component twice weekly 4

Administration Schedule

• Preferred schedule: Monday-Tuesday-Wednesday (3 consecutive days)
• Alternative schedule: Monday and Thursday (2 non-consecutive days)
• Each daily dose should be divided into two doses given 12 hours apart

Formulation Considerations

For a 10kg child, using pediatric suspension is most appropriate:

• Co-trimoxazole pediatric suspension typically contains 40mg trimethoprim + 200mg sulfamethoxazole per 5mL
• Approximately 9-10mL per day (divided into two 4.5-5mL doses) on prophylaxis days

Duration of Prophylaxis

• PCP prophylaxis should be continued throughout the entire duration of maintenance chemotherapy for B-ALL 5
• Evidence suggests that continuing prophylaxis throughout maintenance therapy is important for preventing PCP and may have additional benefits 5

Monitoring and Safety

• Complete blood count with differential should be monitored monthly 4
• Watch for potential adverse effects:
  • Dermatologic reactions (most common): maculopapular rash, urticaria 1
  • Hematologic toxicity: leukopenia, thrombocytopenia 1
  • Rare but serious: Stevens-Johnson syndrome, exfoliative dermatitis (1/200,000 courses) 4

Special Considerations

• Co-trimoxazole is contraindicated in children less than 2 months of age 4, 6
• If co-trimoxazole cannot be tolerated, alternative agents include:
  • Dapsone (2 mg/kg/day) 7 - requires monitoring for methemoglobinemia
  • Atovaquone (30-40 mg/kg/day in 2 divided doses) 1

Important Clinical Pearls

• Lower doses of co-trimoxazole than traditionally recommended may still be effective for PCP prophylaxis 8
• Co-trimoxazole prophylaxis may influence methotrexate/6-mercaptopurine dosing during maintenance therapy, potentially requiring dose adjustments 5
• Co-trimoxazole appears to be well-tolerated in pediatric patients with ALL, with relatively low rates of serious adverse effects compared to adult HIV patients 1

The evidence strongly supports using co-trimoxazole for PCP prophylaxis in children with B-ALL, as it effectively prevents this potentially fatal complication with an acceptable safety profile.