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What the label lists and what reports show

Pyrimethamine side effects

Pyrimethamine's FDA label lists its adverse reactions in its own words. FAERS holds 1,262 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is nausea (134 reports).

  • Generic listed

Check it at the source: the pyrimethamine FDA label on DailyMed (effective December 7, 2023, TILDE Sciences LLC); the FDA FAERS public dashboard.

What does the label list?

From the label: adverse reactions

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; …

Source: FDA drug label, TILDE Sciences LLC, effective December 7, 2023 (SPL set f634f34b-0952-4dd3-9da3-f84b6ab823de), via openFDA; the full label on DailyMed

What do FAERS reports show?

1,262 reports list pyrimethamine among the medicines taken, each a report of something that happened, not proof the medicine caused it; 220 are coded as a death and 533 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 20 reactions below, 5 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.

Reports received each year

The 25 most reported reactions

  • Off Label Use (a use or a product term, not a reaction)164
  • Nausea134
  • Vomiting (named in the label)101
  • Pancytopenia (named in the label)87
  • Drug Ineffective (a use or a product term, not a reaction)73
  • Neutropenia (named in the label)72
  • Pyrexia64
  • Headache63
  • Dizziness50
  • Acute Kidney Injury49
  • Death (an outcome recorded in the report)49
  • Rash49
  • Cerebral Toxoplasmosis47
  • Diarrhoea47
  • Thrombocytopenia (named in the label)43
  • Pain36
  • Asthenia35
  • Condition Aggravated (a use or a product term, not a reaction)34
  • Bone Marrow Failure33
  • Dyspnoea33
  • Toxoplasmosis (a use or a product term, not a reaction)32
  • Renal Failure31
  • Fatigue30
  • Anaemia (named in the label)28
  • Insomnia28

Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms

What next?

Pyrimethamine: the full record
label, generics, price, shortages, recalls
Side effects hub
the most reported medicines and reactions