Sulfadoxine competitively inhibits dihydropteroate synthase, interfering with folate synthesis.
It was previously used to prevent malaria but due to high levels of resistance, this use is no longer recommended routinely.
It is also used, usually in combination with other drugs, to treat or prevent various infections in livestock.
For completeness, all major reactions to sulfonamides and to pyrimethamine are included below, even though they may not have been reported with Fansidar.
Agranulocytosis, aplastic anemia, megaloblastic anemia, thrombocytopenia, leukopenia, hemolytic anemia, purpura, hypoprothrombinemia, methemoglobinemia, and eosinophilia.
Skin and Miscellaneous Sites Allergic Reactions
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, allergic myocarditis, slight hair loss, Lyell's syndrome,
Glossitis, stomatitis, nausea, emesis, abdominal pains, hepatitis, hepatocellular necrosis, diarrhea, pancreatitis, feeling of fullness, and transient rise of liver enzymes.
Central Nervous System Reactions
Headache, peripheral neuritis, mental depression, convulsions, ataxia, hallucinations, tinnitus, vertigo, insomnia, apathy, fatigue, muscle weakness, nervousness, and polyneuritis.
Pulmonary infiltrates resembling eosinophilic or allergic alveolitis.
Renal failure, interstitial nephritis, BUN and serum creatinine elevation, toxic nephrosis with oliguria and anuria, and crystalluria.
Drug fever, chills, periarteritis nodosa and LE phenomenon have occurred.
The sulfonamides bear certain chemical similarities to some goitrogens, diuretics(acetazolamide and the thiazides), and oral hypoglycemic agents. Diuresis and hypoglycemia have occurred rarely in patients receiving sulfonamides. Cross-sensitivity may exist with these agents. Rats appear to be especially susceptible to the goitrogenic effects of sulfonamides, and long-term administration has produced thyroid malignancies in the species.
The dosage should be swallowed whole, and not chewed, with plenty of fluids after a meal.
There have been reports which may indicate an increase in incidence and severity of adverse reactions when chloroquine is used with Fansidar (sulfadoxine and pyrimethamine) as compared to the use of Fansidar (sulfadoxine and pyrimethamine) alone. Fansidar (sulfadoxine and pyrimethamine) is compatible with quinine and with antibiotics. However, antifolic drugs such as sulfonamides, trimethoprim, or trimethoprim-sulfamethoxazole combinations should not be used while the patient is receiving Fansidar (sulfadoxine and pyrimethamine) for antimalarial prophylaxis. Fansidar (sulfadoxine and pyrimethamine) has not been reported to interfere with antidiabetic agents.
If signs of folic acid deficiency develop, Fansidar (sulfadoxine and pyrimethamine) should be discontinued. When recovery of depressed platelets or white blood cell counts in patients with drug-induced folic acid deficiency is too slow, folinic acid (leucovorin) may be administered in doses of 5 to 15 mg intramuscularly daily for 3 days or longer.
Fatalities associated with the administration of sulfonamides, although rare, have occurred due to severe reactions, including fulminant hepatic necrosis, agranulocytosis, aplastic anemia and other blood dyscrasias. Fansidar (sulfadoxine and pyrimethamine)prophylactic regimen has been reported to cause leukopenia during a treatment of 2 months or longer. This leukopenia is generally mild and reversible.
Oral Fansidar (sulfadoxine and pyrimethamine) has not been evaluated for the treatment of cerebral malaria or other severe manifestations of complicated malaria, including hyperparasitemia, pulmonary edema or renal failure. Patients with severe malaria are not candidates for oral therapy. In the event of recrudescent P. falciparum infections after treatment with Fansidar (sulfadoxine and pyrimethamine) or failure of chemoprophylaxis with Fansidar (sulfadoxine and pyrimethamine) , patients should be treated with a different blood schizonticide.