Septran (Co-trimoxazole) Prophylaxis Dosing in Neutropenic Children with AIHA
Recommended Prophylactic Dose
For PCP prophylaxis in neutropenic children with AIHA, administer co-trimoxazole at 150 mg/m² trimethoprim with 750 mg/m² sulfamethoxazole per day, divided into two doses, given on 3 consecutive days per week. 1
Dosing Algorithm by Body Surface Area
The following weight-based dosing achieves the target prophylactic dose 2:
- Body surface area 0.26-0.53 m²: ½ tablet (single strength) every 12 hours on treatment days 2
- Body surface area 1.06 m²: 1 tablet (single strength) every 12 hours on treatment days 2
- Maximum daily dose: Do not exceed 1,600 mg sulfamethoxazole with 320 mg trimethoprim 1, 2
Critical Monitoring Requirements
Complete blood counts with differential and platelet counts must be performed at initiation and monthly intervals to detect hematologic toxicity, particularly given the existing neutropenia and AIHA. 1
Specific Hematologic Concerns in This Population
- Neutropenia occurs in 12-34% of children receiving TMP-SMX, most commonly during the first week of treatment 3
- The sulfonamide component can theoretically worsen hemolysis in G6PD deficiency, though this is rare 1
- TMP-SMX has been safely used in autoimmune neutropenia with reduction in infection incidence and no adverse effects in small studies 4
- Thrombocytopenia develops in approximately 12% of children, typically between days 7-16 of treatment 3
Important Clinical Pitfalls
Do not use TMP-SMX in children under 2 months of age due to bilirubin displacement concerns. 2
Folinic acid supplementation should be considered in children developing neutropenia on TMP-SMX prophylaxis, as it significantly increases neutrophil counts without compromising efficacy. 5
Management of Adverse Reactions
Non-Life-Threatening Reactions
- For mild rash, fever, or mild cytopenias: temporarily discontinue and retry within 2 weeks 1, 6
- Desensitization protocols allow up to 70% of patients to tolerate rechallenge 6
- After successful desensitization, give TMP-SMX daily (not intermittently) to prevent serious reactions upon reintroduction 1
Life-Threatening Reactions
Alternative Prophylactic Regimens if TMP-SMX Not Tolerated
Dapsone 1 mg/kg/day orally (maximum 100 mg/day), with monthly CBC monitoring 1
Aerosolized pentamidine for children ≥5 years: 300 mg every 4 weeks via Respirgard II nebulizer 1
Intravenous pentamidine 4 mg/kg every 2-4 weeks for children who cannot tolerate other options 1, 7
Rationale for This Approach
The intermittent 3-day-per-week regimen minimizes toxicity while maintaining efficacy, as demonstrated in children with cancer where no PCP episodes occurred with this schedule compared to 21% in placebo groups. 1 This is particularly important in AIHA patients where additional bone marrow suppression must be avoided while preventing life-threatening opportunistic infections in the setting of neutropenia.