Bactrim (TMP-SMX) Dosing for PCP Prophylaxis
The recommended dosing for Bactrim (trimethoprim/sulfamethoxazole) for Pneumocystis jirovecii pneumonia prophylaxis in adults is one double-strength tablet (800 mg sulfamethoxazole/160 mg trimethoprim) daily. 1
Primary Prophylaxis Regimens
First-line regimen:
Alternative effective regimens:
- TMP-SMX one single-strength tablet (400 mg SMX/80 mg TMP) daily 1, 2
- TMP-SMX one double-strength tablet three times weekly 1, 2
Indications for PCP Prophylaxis
Prophylaxis should be initiated for HIV-infected patients with:
- CD4+ T lymphocyte count <200 cells/μL
- CD4+ T lymphocyte percentage <14%
- History of oropharyngeal candidiasis
- History of AIDS-defining illness
- Constitutional symptoms like unexplained fever >100°F for ≥2 weeks 1, 2
Alternative Agents When TMP-SMX Cannot Be Tolerated
If TMP-SMX cannot be tolerated, alternative regimens include:
- Dapsone 100 mg daily
- Dapsone plus pyrimethamine plus leucovorin
- Aerosolized pentamidine 300 mg once monthly via Respirgard II nebulizer
- Atovaquone 1500 mg daily 1, 2
Special Considerations
Adverse Reactions Management
- For non-life-threatening adverse reactions, continue TMP-SMX if clinically feasible
- Consider reintroducing TMP-SMX after adverse reactions resolve, with options including gradual dose increase (desensitization) or reduced dose/frequency
- Up to 70% of patients can tolerate reinstitution of therapy 1
Monitoring
- Complete blood counts with differential and platelet count should be performed at initiation of TMP-SMX prophylaxis and monthly during prophylaxis 1
Important Caveats
- TMP-SMX provides cross-protection against toxoplasmosis and common respiratory bacterial infections 1
- Aerosolized pentamidine provides no protection against extrapulmonary pneumocystosis and is less effective than TMP-SMX 1
- Evaluate patients for tuberculosis before initiating therapy 1
- Monitor for drug interactions, particularly with methotrexate 1
- Despite prophylaxis, breakthrough infections can still occur, as documented in case reports 3
Pediatric Dosing
For children ≥1 month of age, the recommended dose is:
- 150 mg TMP with 750 mg SMX/m² body surface area per day, divided and given 3 days per week
- Total daily dose should not exceed 320 mg TMP with 1600 mg SMX 1, 4
TMP-SMX remains the most effective agent for PCP prophylaxis with the strongest evidence base. The three-times-weekly regimen has been shown to be effective in multiple studies 5 and may be associated with fewer adverse effects while maintaining efficacy.