Take this medication by mouth as directed by your doctor, usually once or twice daily. Take this medication with food to decrease nausea and vomiting. If vomiting is severe or continues, your doctor may lower your dose or direct you to stop taking this medication. Your doctor will prescribe another medication (folic/folinic acid) to prevent blood problems caused by pyrimethamine. Follow your doctor's directions carefully. Drink plenty of fluids to prevent kidney problems if you are taking a "sulfa" medication with pyrimethamine.

This medication works best when the amount of drug in your body is kept at a constant level. Take this drug and other antiparasitic drugs regularly, exactly as prescribed by your doctor. To help you remember, take it at the same time(s) each day.

Dosage is based on the type of infection, your medical condition, age, and response to treatment. The length of time you will take this medication depends on your infection. Your dose must be carefully adjusted by your doctor to treat your infection and prevent serious side effects. Follow your doctor's directions carefully.

Do not take more or less of this drug than prescribed. Do not stop taking it before completing this prescription unless directed to do so by your doctor, even if you feel better. Skipping or changing your dose without approval from your doctor may cause the amount of parasites to increase, make the infection more difficult to treat (resistant), or worsen side effects.

Tell your doctor if your condition lasts or gets worse.