Pyrimethamine

What it is and how it works

Mechanism class: Dihydrofolate Reductase Inhibitors

Indications

INDICATIONS AND USAGE Treatment of Toxoplasmosis : Pyrimethamine tablets are indicated for the treatment of toxoplasmosis when used conjointly with a sulfonamide, since synergism exists with this combination.

Dosage and administration (summary)

DOSAGE AND ADMINISTRATION For Treatment of Toxoplasmosis : The dosage of pyrimethamine tablets for the treatment of toxoplasmosis must be carefully adjusted so as to provide maximum therapeutic effect and a minimum of side effects. At the dosage required, there is a marked variation in the tolerance to the drug. Young patients may tolerate higher doses than older individuals. Concurrent administration of folinic acid is strongly recommended in all patients. The adult starting dose is 50 to 75 mg of the drug daily, together with 1 to 4 g daily of a sulfonamide of the sulfapyrimidine type, e.g. sulfadoxine.

Contraindications

CONTRAINDICATIONS Use of pyrimethamine tablets are contraindicated in patients with known hypersensitivity to pyrimethamine or to any component of the formulation. Use of the drug is also contraindicated in patients with documented megaloblastic anemia due to folate deficiency.

Warnings and precautions

WARNINGS The dosage of pyrimethamine required for the treatment of toxoplasmosis has a narrow therapeutic window . If signs of folate deficiency develop (see ADVERSE REACTIONS ), reduce the dosage or discontinue the drug according to the response of the patient. Folinic acid (leucovorin) should be administered in a dosage of 5 to 15 mg daily (orally, intravenous, or intramuscular) until normal hematopoiesis is restored. Data in 2 humans indicate that pyrimethamine may be carcinogenic.

Pregnancy

Pregnancy Teratogenic Effects : Pyrimethamine has been shown to be teratogenic in rats when given in oral doses 2.5 times the human dose for treatment of toxoplasmosis. At these doses in rats, there was a significant increase in abnormalities such as cleft palate, brachygnathia, oligodactyly, and microphthalmia.

Storage and supply

HOW SUPPLIED Pyrimethamine Tablets, USP are available as following: 25 mg - White, round, scored tablets debossed with “2P” and “T” on one side and plain on the other side in bottles of 30 (NDC 0480-3720-56) and 100 (NDC 0480-3720-01). Store at 15° to 25°C (59° to 77°F) in a dry place and protect from light.

Source: Pyrimethamine (Pyrimethamine) — US FDA prescribing information, 2021-08-19, DailyMed. Summarised and shortened; the full label governs. Iranian registration, indications and labelling may differ.