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Pyrimethamine Side Effects

Medically reviewed by Last updated on May 8, 2022.

For the Consumer

Applies to pyrimethamine: oral tablet

Side effects requiring immediate medical attention

Along with its needed effects, pyrimethamine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking pyrimethamine:


  • Chest pain
  • dry cough
  • fever
  • rapid or trouble breathing
  • skin rash
  • unusual tiredness or weakness

Incidence not known

  • Black, tarry stools
  • bleeding gums
  • blistering, peeling, or loosening of the skin
  • blood in the urine or stools
  • chills
  • cough
  • diarrhea
  • difficulty swallowing
  • dizziness
  • fainting spells
  • fast or irregular heartbeat
  • hives, itching
  • irritation or soreness of the tongue
  • joint or muscle pain
  • lower back or side pain
  • puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
  • painful or difficult urination
  • pale skin
  • pinpoint red spots on the skin
  • red, irritated eyes
  • red skin lesions, often with a purple center
  • sore throat
  • sores, ulcers, or white spots on the lips or in the mouth
  • swollen glands
  • tightness in the chest
  • unusual bleeding or bruising

Side effects not requiring immediate medical attention

Some side effects of pyrimethamine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Incidence not known

For Healthcare Professionals

Applies to pyrimethamine: compounding powder, oral tablet


Since this drug is coadministered with a sulfonamide, the manufacturer product information for the relevant sulfonamide should be consulted for sulfonamide-related side effects.[Ref]


Very common (10% or more): Nausea, vomiting, diarrhea, colic

Uncommon (0.1% to 1%): Dry mouth, dry throat

Very rare (less than 0.01%): Buccal ulceration

Frequency not reported: Glossitis, atrophic glossitis[Ref]

Nervous system

Precipitation of a grand mal attack in a patient predisposed to epilepsy was reported; clinical significance was not established.[Ref]

Very common (10% or more): Headache

Common (1% to 10%): Dizziness

Very rare (less than 0.01%): Convulsions/seizures

Frequency not reported: Ataxia, tremors, precipitation of grand mal attack[Ref]


Very common (10% or more): Anemia

Common (1% to 10%): Thrombocytopenia, leukopenia

Very rare (less than 0.01%): Pancytopenia

Frequency not reported: Megaloblastic anemia, neutropenia, agranulocytosis[Ref]


Very common (10% or more): Rash

Uncommon (0.1% to 1%): Abnormal skin pigmentation, dermatitis


Uncommon (0.1% to 1%): Fever, malaise


Insomnia was reported when this drug was given weekly at higher than recommended doses.

Uncommon (0.1% to 1%): Depression

Very rare (less than 0.01%): Insomnia


Rare (0.01% to 0.1%): Pulmonary eosinophilia

Very rare (less than 0.01%): Pneumonia with cellular and eosinophilic pulmonary infiltration[Ref]

Pneumonia with cellular and eosinophilic pulmonary infiltration was observed when this drug was administered once a week with sulfadoxine.[Ref]


Frequency not reported: Hypersensitivity reactions (included erythema multiforme, Stevens-Johnson Syndrome, toxic epidermal necrolysis, Lyell's syndrome, hepatitis, anaphylaxis, pulmonary reactions, maculopapular rashes)[Ref]


Circulatory collapse was reported in patients treated with higher than recommended doses.[Ref]

Very rare (less than 0.01%): Circulatory collapse

Frequency not reported: Disorders of cardiac rhythm, arrhythmias[Ref]


Hyperphenylalaninemia was reported in neonates treated for congenital toxoplasmosis.[Ref]

Very rare (less than 0.01%): Hyperphenylalaninemia

Frequency not reported: Anorexia[Ref]


Very rare (less than 0.01%): Hematuria


A 51-year-old female developed chronic granulocytic leukemia after taking this drug for 2 years for toxoplasmosis and a 56-year-old patient developed reticulum cell sarcoma after taking this drug for 14 months for toxoplasmosis.[Ref]

Frequency not reported: Chronic granulocytic leukemia, reticulum cell sarcoma[Ref]


1. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0

2. Cerner Multum, Inc. "Australian Product Information." O 0

3. "Product Information. Daraprim (pyrimethamine)." Glaxo Wellcome (2001):

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5. West LJ, Phillips-Howard PA "Serious adverse drug reactions to pyrimethamine-sulphadoxine pyrimethamine-dapsone and to amodiaquine in Britain." J R Soc Med 83 (1990): 82-5

6. Christensen KD, Olsen VV, Loft S "Serious reactions during malaria prophylaxis with pyrimethamine- sulfadoxine." Lancet 2 (1982): 994

7. Concannon AJ, Nicholls MD "Maloprim-induced agranulocytosis and red-cell aplasia." Med J Aust 2 (1982): 564-6

8. Barker LC, Barton CJ, Naik RB, Booth F "Agranulocytosis during malaria prophylaxis with Maloprim (pyrimethamine and dapsone)." Postgrad Med J 60 (1984): 566-7

9. Bowcock SJ, Linch DC, Stewart JW, Machin SJ "Pyrimethamine in the myeloproliferative disorders: a forgotten treatment?" Clin Lab Haematol 9 (1987): 129-36

10. Whitehead S "Agranulocytosis associated with maloprim." Br Med J (Clin Res Ed) 286 (1983): 1515

11. Fiore T, Iaccheri B, Papadaki T, et al. "Adverse drug reactions to treatments for ocular toxoplasmosis: A retrospective chart review." Clin Ther 30 (2008): 2069-74

12. Alexander J, Taylor S, Kuritsky JN, Miller KD, Perez TH, Howrie DL, Van Thiel DH, Zitelli BJ "Fatal hepatic necrosis due to pyrimethamine-sulfadoxine (Fansidar)." Ann Intern Med 106 (1987): 393-5

13. Cameron IR, Bateman C, Shovlin C, Burton GH, Davidson AC, Marrinan M "Pulmonary toxicity of malaria prophylaxis." BMJ 297 (1988): 1240-1

14. Ladusans EJ, Smith PG, Selby CD "Fatal multisystemic toxicity associated with prophylaxis with pyrimethamine and sulfadoxine (Fansidar)." Br Med J (Clin Res Ed) 290 (1985): 113-4

15. Gustafsson L, Rombo L, Svanbom M "Unusual pulmonary reaction during short term prophylaxis with pyrimethamine-sulfadoxine (Fansidar)." Br Med J (Clin Res Ed) 288 (1984): 1876

16. Whitfield D "Presumptive fatality due to pyrimethamine-sulfadoxine." Lancet 2 (1982): 1272

17. Behrens RH, Dunlop J, Phillips-Howard PA "Stevens-Johnson syndrome due to pyrimethamine/sulfadoxine during presumptive self-therapy of malaria." Lancet 2 (1989): 803-4

18. "Fansidar-associated fatal reaction in an HIV-infected man." MMWR Morb Mortal Wkly Rep 37 (1988): 571-2

19. Hornstein OP, Ruprecht KW "Fansidar-induced Stevens-Johnson Syndrome." N Engl J Med 307 (1982): 1529-30

20. Jeffrey RF "Transient lupus anticoagulant and fansidar therapy." Postgrad Med J 62 (1986): 893-4

21. Adams SJ, Broadbent J, Clayden LM, Ridley CM "Erythema multiforme (Stevens-Johnson) precipitated by Fansidar." Postgrad Med J 61 (1985): 263-4

22. McCormack D, Morgan WK "Fansidar hypersensitivity pneumonitis." Br J Dis Chest 81 (1987): 194-6

23. Tanner NS, Ward DJ, Krzeminska EC "Treatment of toxic epidermal necrolysis and a review of six cases." Burns 16 (1990): 97-104

24. Sivayathorn A, Honigsmann H, Ortel B "An unusual combination of phototoxicity and Stevens-Johnson syndrome due to antimalarial therapy." Dermatologica 178 (1989): 39-42

25. Bamber MG, Elder AT, Gray JA, Minns RA "Fatal Stevens-Johnson syndrome associated with Fansidar and chloroquine." J Infect 13 (1986): 31-3

26. Pang JA "Non-cardiogenic pulmonary oedema associated with pyrimethamine." Respir Med 83 (1989): 247-8

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.