Bactrim Dosing for PCP Prophylaxis in Patients on High-Dose Steroids
For patients on high-dose corticosteroids (≥20 mg prednisone equivalent daily for ≥4 weeks), administer trimethoprim-sulfamethoxazole (TMP-SMX) one double-strength tablet (800 mg SMX/160 mg TMP) three times weekly on Monday, Wednesday, and Friday. 1, 2
Recommended Prophylactic Regimen
The Monday-Wednesday-Friday dosing schedule is explicitly endorsed as a standard prophylaxis regimen across multiple guidelines:
- One double-strength tablet (800/160 mg) three times weekly is the recommended dosing for immunocompromised patients requiring PCP prophylaxis 2
- This regimen provides adequate protection while minimizing adverse effects compared to daily dosing 1, 2
- The Centers for Disease Control and Prevention confirms TMP-SMX as the first-line prophylactic agent due to superior efficacy over alternatives 2
Duration of Prophylaxis
Continue prophylaxis throughout the entire period of high-dose steroid therapy and for at least 2-4 weeks after discontinuation or dose reduction below 20 mg/day prednisone equivalent. 1, 3
- For patients on glucocorticoids >15-30 mg/day for >2-4 weeks, prophylaxis should continue despite potential cytopenias 3
- Liver transplant recipients should receive prophylaxis for 6-12 months post-transplant 1
- Patients receiving alemtuzumab require prophylaxis for minimum 2 months after therapy and until CD4 count >200 cells/μL 1
Alternative Regimens
If the three-times-weekly regimen is not tolerated, consider these options in order of preference:
- One double-strength tablet daily (800/160 mg) provides maximum protection but higher adverse effect risk 2, 4
- Dapsone 100 mg daily for patients with TMP-SMX intolerance (must exclude G6PD deficiency first) 2, 3, 5
- Atovaquone 1500 mg daily as second-line alternative 2, 3
- Aerosolized pentamidine 300 mg monthly for severe TMP-SMX intolerance 6
Important Monitoring and Precautions
Perform complete blood count with differential and platelet count at initiation and monthly during therapy. 3
Common adverse effects to monitor include:
- Rash, pruritus, and hypersensitivity reactions 2
- Cytopenias (leukopenia, thrombocytopenia, anemia) 2, 3
- Transaminase elevations (particularly relevant in liver disease) 2, 7
Critical Drug Interaction
If the patient is also receiving methotrexate, the three-times-weekly prophylactic dose (800/160 mg) is generally well tolerated, but higher doses (800/160 mg twice daily) carry significant risk of severe bone marrow suppression. 1
- The interaction occurs because both drugs inhibit folate metabolism 1
- Monitor closely for cytopenias when combining these agents 1
- Lower prophylactic doses (three times weekly or 400/80 mg daily) are safer with concurrent methotrexate 1
Special Populations
For patients with renal impairment requiring prophylaxis:
- Creatinine clearance 15-30 mL/min: Reduce to half the usual regimen 4
- Creatinine clearance <15 mL/min: TMP-SMX use not recommended; switch to alternative agent 4
For pediatric patients on chemotherapy: