Pyrimethamine is a medication used to treat malaria and toxoplasmosis, a parasitic infection. This drug is classified as an antiparasitic medicine. It inhibits the reproduction and growth of parasites. Pyrimethamine can be further classified as an antiprotozoal drug, which means that it specifically targets tiny protozoa parasites. It may also be used for treating pneumocystis carinii pneumonia, a fungal infection in the lungs, as well as isosporiasis, an intestinal disease.
A small meal or snack may be eaten with each dose of pyrimethamine, if patients experience nausea or an upset stomach. This drug should be taken with a full glass of water. Those taking it for malaria may be prescribed up to three doses daily. Doses should be taken at regular intervals throughout the day for best results.
Adults will typically take 25 milligrams (mg) of pyrimethamine daily for two days when using it to treat malaria. They will typically be prescribed an additional medication, such as a sulfonamide. To treat toxoplasmosis and similar infections, adults will typically take a total of 50 to 75 mg daily for about one to three weeks. All dosages for children are based on body weight.
Patients must be aware of the early symptoms of potentially dangerous side effects from using pyrimethamine. They must discontinue the medication and get medical help immediately if they experience a skin rash or excessive paleness of the skin, unusual bruising, or a sore throat. Swelling of the tongue may also occur. Signs of an allergic reaction may include difficulty breathing, hives, and closing of the throat, as well as facial swelling.
Other possible side effects can include nausea, vomiting, and the loss of appetite. Some patients have reported insomnia and lightheadedness. Dry mouth and headache may occur. The doctor should be informed if any of these side effects become severe or bothersome.
Certain patients may be unable to take pyrimethamine, because of other medical conditions. This includes those who have liver or kidney disease. People with a seizure disorder, folate deficiency, or those who have previously had a reaction to this medication may also be unable to use it. There is insufficient evidence for the risk to an unborn baby, therefore pregnant women may be unable to use it. It may potentially harm a nursing infant.
Pyrimethamine may interact with other medications, such as lorazepam, aurothioglucose, and methotrexate. Patients should disclose all other medicines they use. The doctor will evaluate the potential risk of interactions versus the benefit of the drugs.