Recommended Dosage of Bactrim for PJP Prophylaxis
The recommended dosage of Bactrim (trimethoprim/sulfamethoxazole) for Pneumocystis jirovecii pneumonia (PJP) prophylaxis is one double-strength tablet (800 mg sulfamethoxazole/160 mg trimethoprim) three times weekly. 1
Standard Prophylactic Regimens
The most widely recommended prophylactic regimens for PJP include:
- First-line option: One double-strength tablet (800 mg SMX/160 mg TMP) three times weekly 2, 1
- Alternative options:
Patient Populations Requiring PJP Prophylaxis
Prophylaxis should be considered for:
- Patients on triple immunosuppressive therapy, particularly those on:
- Corticosteroids (especially doses >15-30 mg prednisolone or equivalent for >2-4 weeks)
- Thiopurine
- AND either a calcineurin inhibitor or infliximab 2
- Patients with multiple myeloma receiving bispecific antibody therapy 2
- Patients with other autoimmune inflammatory rheumatic diseases on high-dose glucocorticoids, especially when combined with other immunosuppressants 2
Alternative Options for Patients with Sulfa Allergy
For patients with sulfa allergies, the following alternatives are recommended:
- Dapsone 100 mg daily 2, 1
- Atovaquone 1500 mg daily 2, 1
- Aerosolized pentamidine 300 mg once monthly via Respirgard II nebulizer 1
Monitoring During Prophylaxis
- Complete blood counts with differential and platelet count should be performed:
- At initiation of TMP-SMX prophylaxis
- Monthly during prophylaxis 1
- Evaluate patients for tuberculosis before initiating therapy 1
- Monitor for drug interactions, particularly with methotrexate 1
Important Considerations and Precautions
- TMP-SMX remains the most effective agent for PJP prophylaxis with the strongest evidence base 1
- Common adverse effects of TMP-SMX include rash, pruritus, cytopenias, and transaminase elevations 1
- For non-life-threatening adverse reactions, consider continuing TMP-SMX if clinically feasible 1
- Up to 70% of patients can tolerate reinstitution of therapy after adverse reactions resolve 1
- Risk factors for PJP include persistent lymphopenia, older age, and pre-existing lung disease 2
Pediatric Dosing
For children, the FDA-approved dosage for PJP prophylaxis is:
- 750 mg/m²/day sulfamethoxazole with 150 mg/m²/day trimethoprim given orally in equally divided doses twice a day, on 3 consecutive days per week
- The total daily dose should not exceed 1600 mg sulfamethoxazole and 320 mg trimethoprim 3
The three-times-weekly regimen of TMP-SMX has been shown to be effective in multiple studies and is the standard of care for PJP prophylaxis in immunocompromised patients, balancing efficacy with minimizing adverse effects.