Trimethoprim

FDA label

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Renal CrCl 15-30: 50 mg q12h; CrCl <15: not recommended

Hepatic No dose guidance; give with caution in hepatic impairment

Instructions

• Complete the full 10-day course even if feeling better

Available strengths

• tab 100 mg

Contraindications

• Documented megaloblastic anemia due to folate deficiency

Cautions

• Hematologic toxicity: may interfere with hematopoiesis (esp. large doses/prolonged use); sore throat, fever, pallor, or purpura may herald serious blood disorder — obtain CBC and discontinue if a formed element significantly reduced
• Give with caution in possible folate deficiency (folates may be co-administered without loss of antibacterial effect)
• Rare serious hypersensitivity reactions (exfoliative dermatitis, SJS, TEN, anaphylaxis)
• C. difficile-associated diarrhea (mild to fatal colitis), up to >2 months post-treatment
• Caution in renal or hepatic impairment
• Elderly: greater renal-impairment risk; consider monitoring potassium and creatinine clearance (hyperkalemia case reports)
• Effectiveness as single agent not established in children <12 y; safety not established <2 months

Adverse reactions

• Rash and pruritus (most common; 2.9-6.7% at recommended doses), phototoxic skin eruptions
• GI: epigastric distress, nausea, vomiting, glossitis; rare cholestatic jaundice; transaminase/bilirubin elevation
• Hematologic: thrombocytopenia, leukopenia, neutropenia, megaloblastic anemia, methemoglobinemia
• Hyperkalemia, hyponatremia
• Rare: SJS/TEN, anaphylaxis, aseptic meningitis; fever, BUN/creatinine increases

Pregnancy Category C; teratogenic in animals at high doses; may interfere with folate metabolism — use only if potential benefit justifies fetal risk

Lactation Excreted in human milk; caution (folate metabolism interference)