II. Indications
-
Toxoplasmosis in immunocompetent patients (FDA approved)
- Has been used off label for Toxoplasmosis in HIV and Congenital Toxoplasmosis
- Previously used to treat Malaria
III. Contraindications
-
G6PD Deficiency
- Risk of Hemolytic Anemia
IV. Mechanism
- Synthetic derivative of ethyl Pyrimidine with Antiparasitic and antimalarial activity
- Competitive inhibitor of dihydrofolate reductase (DHFR).
- DHFR is a key enzyme in Tetrahydrofolate synthesis, and in turn DNA and Protein synthesis
V. Medications
- Tablet: 25 mg
- Only available directly from manufacturer
VI. Dosing: Toxoplasmosis in Immunocompetent Patients
- Used in combination with leucovorin and Sulfadiazine
- Combined with leucovorin to prevent hematologic adverse effects
- Combined with Sulfadiazine to broaden coverage
- Dosing is for immunocompetent patients
- See other resources for HIV related ToxoplasmosisEncephalitis
- See other resources for Congenital Toxoplasmosis
- Adult
- Start 50 to 75 mg orally daily for 1 to 3 weeks (use lower dose in Seizure Disorder)
- Next decrease dose 50% daily for an additional 5 weeks
- Child
- Start 1 mg/kg/day orally twice daily for 2 to 4 days
- Next decrease dose 50% for an additional 4 weeks
VII. Adverse Effects
-
Hypersensitivity Reaction
- Most commonly presents as a Cutaneous Drug Eruption (esp. when combined with a Sulfonamide)
- Hematologic Effects
- Thrombocytopenia, Leukopenia, and Anemia may occur
- Hemolytic Anemia with G6PD
- Gastrointestinal
-
Folate Deficiency
- Dose dependent
- Neurologic
VIII. Safety
- Pregnancy Category C
- Considered safe in Lactation
IX. Resources
- Pyrimethamine Tablet (DailyMed)