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Pyrimethamine / sulfadoxine Side Effects

Medically reviewed by Last updated on Jan 15, 2024.

Applies to pyrimethamine / sulfadoxine: oral tablet.


Do not use this medication if you have ever had a serious allergic reaction to pyrimethamine or sulfadoxine. Stop taking the medicine and call your doctor at once if you have any signs of skin rash, no matter how mild.

You should not use this medication if you are allergic to sulfa drugs, or if you have liver or kidney disease (if using the medication long-term), a blood cell disorder (such as anemia), if you are in late pregnancy, or if you are breast-feeding a baby.

Take the pyrimethamine and sulfadoxine tablet after a meal, with plenty of water or other fluid. Swallow the tablet whole, do not break or chew it.

Drink plenty of water to keep your kidneys working and prevent kidney stones while taking this medication.

You should not take pyrimethamine and sulfadoxine for longer than 2 years without a doctor's advice.

In addition to taking pyrimethamine and sulfadoxine, use protective clothing, insect repellents, and mosquito netting around your bed to further prevent mosquito bites that could cause malaria.

No medication is 100% effective in treating or preventing malaria. For best results, keep using the medication as directed. Talk with your doctor if you have fever, vomiting, or diarrhea during your treatment.

Get emergency medical help if you have any of these signs of an allergic reaction while taking pyrimethamine / sulfadoxine: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Stop using pyrimethamine and sulfadoxine and call your doctor at once if you have any of these serious side effects:

Less serious side effects of pyrimethamine / sulfadoxine may include:

This is not a complete list of side effects and others may occur. Tell your doctor about any unusual or bothersome side effect.

For Healthcare Professionals

Applies to pyrimethamine / sulfadoxine: oral tablet.


Severe cutaneous reactions have occurred in patients who have taken as few as two doses of pyrimethamine-sulfadoxine. The risk of fatal cutaneous reactions in patients receiving pyrimethamine-sulfadoxine has been estimated to range from 1 in 11,000 to 1 in 25,000. In general, the use of sulfonamide antibiotics is associated with large increases in the risk of Stevens-Johnson syndrome or toxic epidermal necrolysis, although these phenomena are rare as a whole.[Ref]

Hypersensitivity reactions have included erythema multiforme, Stevens-Johnson syndrome, generalized skin eruptions, toxic epidermal necrolysis, urticaria, serum sickness, pruritus, exfoliative dermatitis, anaphylactoid reactions, periorbital edema, conjunctival and scleral injection, photosensitization, arthralgia, and allergic pericarditis. Fatalities due to severe hypersensitivity reactions have been reported.[Ref]


Dermatologic side effects have frequently included phototoxicity, rash, dermatitis, and hair loss.[Ref]


Hematologic toxicity is more common with higher doses of pyrimethamine.

Many cases of agranulocytosis have occurred during therapy with pyrimethamine-dapsone, although it has been reported in patients receiving pyrimethamine-sulfadoxine as well.[Ref]

Hematologic side effects have included leucopenia (7%), agranulocytosis, aplastic anemia, megaloblastic anemia, thrombocytopenia, hemolytic anemia, purpura, hypoprothrombinemia, methemoglobinemia, and eosinophilia. Macrocytic anemia has also been reported. Fatalities have been reported.[Ref]


Gastrointestinal side effects have included anorexia (5.5%), digestive intolerance (3%), diarrhea (2.74%), abdominal pain (2.74%), vomiting (2.74%), nausea, glossitis, stomatitis, and pancreatitis.[Ref]


Hepatic side effects have included hepatitis (7%), hepatocellular necrosis, and liver enzyme elevations.[Ref]

In many cases, the hepatitis has accompanied severe cutaneous reactions, fever, myalgias and arthralgias. Granulomas and necrosis have been seen on biopsy.[Ref]


Renal side effects have included renal failure, interstitial nephritis, toxic nephrosis with oliguria and anuria, crystalluria, and increases in BUN and serum creatinine.[Ref]


Respiratory side effects have included cough (9.6%), pulmonary infiltrates and shortness of breath which may be due to pulmonary hypersensitivity reactions. Frequently, the pulmonary reactions have accompanied other systemic symptoms.[Ref]

Nervous system

Nervous system side effects have included headache (4.1%), peripheral neuritis, mental depression, convulsions, ataxia, hallucinations, tinnitus, vertigo, insomnia, apathy, fatigue, muscle weakness, nervousness, and polyneuritis.[Ref]


Metabolic side effects associated with sulfonamides have included diuresis and hypoglycemia. Sulfonamides are chemically similar to goitrogenic agents (i.e., diuretics and oral hypoglycemic agents).[Ref]


Genitourinary side effects have included crystalluria.[Ref]


Endocrine side effects including weight gain (1 kg or greater) have been reported in 53% of patients.


Other side effects have included drug fever, chills, periarteritis nodosa, and lupus erythematosus phenomenon.[Ref]


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

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10. Fansidar-associated fatal reaction in an HIV-infected man. MMWR Morb Mortal Wkly Rep. 1988;37:571-2.

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12. Jeffrey RF. Transient lupus anticoagulant and fansidar therapy. Postgrad Med J. 1986;62:893-4.

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

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28. Fish DR, Espir ML. Convulsions associated with prophylactic antimalarial drugs: implications for people with epilepsy. BMJ. 1988;297:526-7.

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.