TRIMPEX 200
Clinical safety rating: caution
Comprehensive clinical and safety monograph for TRIMPEX 200 (TRIMPEX 200).
Trimethoprim inhibits bacterial dihydrofolate reductase, blocking the conversion of dihydrofolic acid to tetrahydrofolic acid, thereby inhibiting bacterial DNA synthesis.
| Metabolism | Hepatic metabolism via cytochrome P450 enzymes (CYP3A4, CYP1A2). |
| Excretion | Renal excretion of unchanged drug accounts for approximately 60-80% of elimination, with an additional 10-20% as hepatic metabolites excreted in bile and feces. |
| Half-life | Terminal elimination half-life is 8-10 hours in adults with normal renal function; prolonged to 20-30 hours in renal impairment (CrCl <30 mL/min), requiring dose adjustment. |
| Protein binding | Approximately 40-50% bound primarily to albumin. |
| Volume of Distribution | 1.2-1.8 L/kg, indicating extensive tissue distribution, with high concentrations in lung and kidney tissues. |
| Bioavailability | Oral: 80-90% with minimal first-pass effect; intravenous: 100%. |
| Onset of Action | Oral: 30-60 minutes; intravenous: 5-10 minutes. |
| Duration of Action | Oral: 8-12 hours; intravenous: 6-8 hours. Duration may be prolonged in renal impairment. |
| Molecular Weight | 290.32 Da |
200 mg orally once daily, or 100 mg orally twice daily.
| Dosage form | TABLET |
| Renal impairment | CrCl >30 mL/min: no adjustment; CrCl 15-30 mL/min: 100 mg once daily; CrCl <15 mL/min: 100 mg every 48 hours. |
| Liver impairment | No adjustment required for mild-to-moderate hepatic impairment (Child-Pugh A/B); use with caution in severe impairment (Child-Pugh C) with dose reduction of 50% recommended. |
| Pediatric use | For children ≥6 years: 5 mg/kg orally once daily, up to 200 mg daily; for children 2-5 years: 4 mg/kg orally once daily, up to 150 mg daily. |
| Geriatric use | No specific dose adjustment, but monitor renal function and consider starting at 100 mg daily due to age-related decline in GFR. |
| 1st trimester | Trimethoprim is a folate antagonist and is associated with an increased risk of neural tube defects and cardiovascular malformations when used in the first trimester. Avoid use if possible. |
| 2nd trimester | Limited data; potential risk of folate antagonism. Use only if clearly needed and consider folic acid supplementation. |
| 3rd trimester | Theoretical risk of neonatal hyperbilirubinemia and hemolytic anemia due to displacement of bilirubin from albumin. Use near term with caution. |
Clinical note
Comprehensive clinical and safety monograph for TRIMPEX 200 (TRIMPEX 200).
| Placental transfer | Trimethoprim crosses the placenta readily, achieving fetal serum concentrations approximately 50-100% of maternal levels. It inhibits fetal folate metabolism. |
| Breastfeeding | Trimethoprim is excreted into breast milk in low concentrations. It is considered compatible with breastfeeding, but caution is advised in nursing infants with glucose-6-phosphate dehydrogenase (G6PD) deficiency due to risk of hemolytic anemia. |
■ FDA Black Box Warning
None.
| Serious Effects |
Known hypersensitivity to trimethoprim or any component of the formulationMegaloblastic anemia due to folate deficiencySevere hepatic or renal impairment (unless closely monitored)
| Precautions | Risk of megaloblastic anemia in patients with folate deficiency, Hypersensitivity reactions including Stevens-Johnson syndrome, Hyperkalemia in elderly or renally impaired patients, Hematologic toxicity (leukopenia, thrombocytopenia) with prolonged use |
| Food/Dietary | Avoid potassium-rich foods (bananas, oranges, potatoes) and potassium supplements as trimethoprim can increase potassium levels. No specific food restrictions but maintain adequate hydration. |
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| Lactation Rating | L2 (Limited Data - Probably Compatible) |
| Teratogenic Risk | Trimethoprim is a folate antagonist. First trimester: Associated with increased risk of neural tube defects (OR 2.8), cardiovascular defects (OR 1.8), and oral clefts (OR 2.0) due to folate antagonism. Second and third trimesters: Risk of megaloblastic anemia and potential for hyperbilirubinemia in neonates; may interfere with fetal folate metabolism. |
| Fetal Monitoring | Monitor maternal complete blood count (CBC) including platelet count, serum folate levels, renal function, and liver function tests. Monitor for signs of megaloblastic anemia. Fetal monitoring: ultrasound for potential neural tube defects if exposed in first trimester; assess for growth restriction. |
| Fertility Effects | No well-documented adverse effects on human fertility. Animal studies show no significant impairment. However, folate antagonism may theoretically affect ovulation or spermatogenesis; clinical data are lacking. |
| Clinical Pearls |
| Trimethoprim is a folate antagonist commonly used in combination with sulfamethoxazole. For TRIMPEX 200 (trimethoprim alone), monitor renal function and potassium levels due to risk of hyperkalemia. Adjust dose in renal impairment (CrCl <30 mL/min: avoid or reduce). Not effective for group A streptococcal pharyngitis. Use with caution in elderly due to increased risk of electrolyte disturbances. |
| Patient Advice | Take exactly as prescribed; complete full course even if you feel better. · Drink plenty of fluids to prevent kidney stones. · Avoid prolonged sun exposure; use sunscreen as this medication may increase sun sensitivity. · Report signs of rash, sore throat, or unusual bruising/bleeding immediately. · Do not take with other medications containing trimethoprim or sulfonamides. |