Pyrimethamine
DARAPRIM
“Daring Primitive method man”
What it isDihydrofolate reductase inhibitor selective for the parasite enzyme; toxoplasmosis.
Why this oneIt is first-line for toxoplasmic encephalitis, given with sulfadiazine.
What limits itMegaloblastic anemia and myelosuppression, so leucovorin is co-given throughout. It is teratogenic.
FDA-approved for
- toxoplasmosis (~1953)
FDA label
Read the full label on DailyMed ↗
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Toxoplasmosis | Adults | 50-75 mg QD with a sulfonamide | 50-75 mg QD x1-3 wk, then reduce to ~half x4-5 wk | |
| Toxoplasmosis | Pediatric | 1 mg/kg/day divided BID | reduce to ~half after 2-4 days, continue ~1 month |
Renal Undefined
Hepatic Undefined
Instructions
- Give with meals to minimize vomiting
- Co-administer folinic acid in all patients
- Use with a sulfapyrimidine-type sulfonamide (e.g., sulfadoxine)
- Younger patients may tolerate higher doses than older individuals
Available strengths
- tab 25 mg
Contraindications
- Documented megaloblastic anemia due to folate deficiency
Cautions
- Hematologic effects (megaloblastic anemia, leukopenia, thrombocytopenia) can occur even at low doses in some patients
- Risk of severe hypersensitivity, especially with concomitant sulfonamide
Adverse reactions
- Severe hypersensitivity (Stevens-Johnson syndrome, TEN, erythema multiforme, anaphylaxis) and hyperphenylalaninemia, esp. with a sulfonamide
- Anorexia, vomiting
- Megaloblastic anemia, leukopenia, thrombocytopenia, pancytopenia, neutropenia, atrophic glossitis, hematuria, cardiac rhythm disorders
- Pulmonary eosinophilia (rare)
Pregnancy No adequate human studies; teratogenic in animals — use only if benefit justifies fetal risk; give folinic acid.
Lactation Undefined
Cost
| Strength | #/mo | generic $/mo | CostPlus | |
|---|---|---|---|---|
| 25 mg | tab | 30 qd | $4,110.26 | offered |
Generic entry2020
NO BOXED WARNINGS
Principal riskMegaloblastic anemia; leucovorin must be co-given
Classes and tags
Clinical profile
Legacy pregnancy categoryUnknown / historical label unavailable
Defining liabilityGenerally tolerated at therapeutic doses; clinically important risks are agent-specific and increase with interactions or organ impairment.
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