pharmacopeia
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/api/v1/drug/pyrimethamine

Mechanism of action

Sourced from openFDA

Mechanism-of-action classes: Dihydrofolate Reductase Inhibitors; Folic Acid Metabolism Inhibitors.

Dihydrofolate ReductaseFolic Acid Metabolism

Indications

Sourced from openFDA
  • Treatment of Toxoplasmosis : Pyrimethamine tablets are indicated for the treatment of toxoplasmosis when used conjointly with a sulfonamide, since synergism exists with this combination.

Contraindications

Sourced from openFDA
  • 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.contraindicated

Dosage & administration

Sourced from openFDA

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. This dosage is ordinarily continued for 1 to 3 weeks, depending on the response of the patient and tolerance to therapy. The dosage may then be reduced to about one half that previously given for each drug and continued for an additional 4 to 5 weeks. The pediatric dosage of pyrimethamine tablets is 1 mg/kg/day divided into 2 equal daily doses; after 2 to 4 days this dose may be reduced to one half and continued for approximately 1 month. The usual pediatric sulfonamide dosage is used in conjunction with pyrimethamine tablets.

Warnings & precautions

Sourced from openFDA

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; a 51-year-old female who developed chronic granulocytic leukemia after taking pyrimethamine for 2 years for toxoplasmosis 3 and a 56-year-old patient who developed reticulum cell sarcoma after 14 months of pyrimethamine for toxoplasmosis. 4 Pyrimethamine has been reported to produce a significant increase in the number of lung tumors in mice when given intraperitoneally at doses of 25 mg/kg. 5 Pyrimethamine tablets should be kept out of the reach of infants and children as they are extremely susceptible to adverse effects from an overdose. Deaths in pediatric patients have been reported after accidental ingestion.

Adverse reactions

Sourced from openFDA

Hypersensitivity reactions, occasionally severe (such as Stevens-Johnson syndrome, toxic epidermal necrolysis, erythema multiforme, and anaphylaxis), and hyperphenylalaninemia, can occur particularly when pyrimethamine is administered concomitantly with a sulfonamide. Consult the complete prescribing information for the relevant sulfonamide for sulfonamide-associated adverse events. With doses of pyrimethamine used for the treatment of toxoplasmosis, anorexia and vomiting may occur. Vomiting may be minimized by giving the medication with meals; it usually disappears promptly upon reduction of dosage. Doses used in toxoplasmosis may produce megaloblastic anemia, leukopenia, thrombocytopenia, pancytopenia, neutropenia, atrophic glossitis, hematuria, and disorders of cardiac rhythm. Hematologic effects, however, may also occur at low doses in certain individuals (see PRECAUTIONS ; General ). Pulmonary eosinophilia has been reported rarely. To report SUSPECTED ADVERSE EVENTS, contact Teva at 1-888-838-2872 or FDA at 1-800-FDA-1088 or http://www.fda.gov/medwatch for voluntary reporting of adverse reactions.

Use in specific populations

Sourced from openFDA

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. Pyrimethamine has also been shown to produce terata such as meningocele in hamsters and cleft palate in miniature pigs when given in oral doses 5 times the human dose for the treatment of toxoplasmosis. There are no adequate and well-controlled studies in pregnant women. Pyrimethamine should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Concurrent administration of folinic acid is strongly recommended when used during pregnancy.

Overdosage

Sourced from openFDA

Following the ingestion of 300 mg or more of pyrimethamine, gastrointestinal and/or central nervous system signs may be present, including convulsions. The initial symptoms are usually gastrointestinal and may include abdominal pain, nausea, severe and repeated vomiting, possibly including hematemesis. Central nervous system toxicity may be manifest by initial excitability, generalized and prolonged convulsions which may be followed by respiratory depression, circulatory collapse, and death within a few hours. Neurological symptoms appear rapidly (30 minutes to 2 hours after drug ingestion), suggesting that in gross overdosage pyrimethamine has a direct toxic effect on the central nervous system. The fatal dose is variable, with the smallest reported fatal single dose being 375 mg. There are, however, reports of pediatric patients who have recovered after taking 375 to 625 mg. There is no specific antidote to acute pyrimethamine poisoning. In the event of overdosage, symptomatic and supportive measures should be employed. Gastric lavage is recommended and is effective if carried out very soon after drug ingestion. Parenteral diazepam may be used to control convulsions.

Approval history

Sourced from openFDA
  • Jan 23, 1953NDANDA008578Tilde Sciences
  • Feb 28, 2020ANDAANDA207127Sanaluz
  • Aug 13, 2021ANDAANDA215506Teva Pharms
  • Oct 25, 2022ANDAANDA216983Aurobindo Pharma Ltd

FAERS reports

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Reference statistics only. FAERS reports are voluntarily submitted and are not incidence rates, safety signals, or causal evidence. Counts reflect reporting volume — how often a reaction was reported, not how often it occurs. For decision-grade use, consult openFDA and the FAERS Public Dashboard directly.
1,238 total reports matchedLatest report Share = reports listing the reaction ÷ total matched reports. Rows can sum to >100% because a single report often lists multiple reactions.
  1. 1Off Label Use15913%
  2. 2Nausea13411%
  3. 3Vomiting1008.1%
  4. 4Pancytopenia836.7%
  5. 5Neutropenia725.8%
  6. 6Drug Ineffective705.7%
  7. 7Pyrexia635.1%
  8. 8Headache625.0%
  9. 9Dizziness504.0%
  10. 10Death494.0%
  11. 11Rash483.9%
  12. 12Acute Kidney Injury473.8%
  13. 13Cerebral Toxoplasmosis473.8%
  14. 14Diarrhoea473.8%
  15. 15Thrombocytopenia423.4%

Literature

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Recent PubMed references pinned to Pyrimethamine as a MeSH major topic. Citations link to pubmed.ncbi.nlm.nih.gov.

Clinical trials

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The 10 most recently updated of 212 ClinicalTrials.gov registrations naming Pyrimethamine as an intervention. Registration is not evidence of efficacy or safety — reference crosswalk only.

Frequently asked questions

How does Pyrimethamine work?
Mechanism-of-action classes: Dihydrofolate Reductase Inhibitors; Folic Acid Metabolism Inhibitors.
What is Pyrimethamine used for?
According to FDA labeling, Pyrimethamine carries indications including: Treatment of Toxoplasmosis : Pyrimethamine tablets are indicated for the treatment of toxoplasmosis when used conjointly with a sulfonamide, since synergism exists with this combination.. This is a reference summary of labeled uses, not medical advice or a treatment recommendation.
What class of drug is Pyrimethamine?
Pyrimethamine is classified as Diaminopyrimidines, Dihydrofolate Reductase Inhibitor Antimalarial, Dihydrofolate Reductase Inhibitors, Folic Acid Metabolism Inhibitors.
What are the brand names for Pyrimethamine?
Pyrimethamine is marketed under brand names including Daraprim, Rebalance.
What are the contraindications for Pyrimethamine?
Pyrimethamine labeling lists contraindications including: 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.. Always consult the full prescribing information and a clinician.
Note. Data for pyrimethamine is illustrative MVP content compiled from public sources. pharmacopeia is for educational and informational use only and is not a substitute for professional medical advice.

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