This medication is used with other medication (such as a sulfonamide) to treat a serious parasite infection (toxoplasmosis) of the body, brain, or eye or to prevent toxoplasmosis infection in people with HIV infection. Rarely, pyrimethamine is used with sulfadoxine to treat malaria. The CDC no longer recommends using pyrimethamine alone to prevent or treat malaria. Pyrimethamine belongs to a class of drugs known as antiparasitics. It works by killing parasites.
OTHER USES: This section contains uses of this drug that are not listed in the approved professional labeling for the drug but that may be prescribed by your health care professional. Use this drug for a condition that is listed in this section only if it has been so prescribed by your health care professional.
Take this medication by mouth usually once or twice daily or as directed by your doctor. 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. Therefore, 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 persists or worsens.
See also How to Use section.
Nausea, vomiting, and loss of appetite may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.
Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.
Some people using this medication may develop serious side effects including blood problems, especially at higher doses. This risk can be reduced with the use of folic/folinic acid and regular blood tests. Tell your doctor immediately if any of these symptoms occur: easy bruising/bleeding, signs of serious infection (such as high fever, severe chills, persistent sore throat), signs of low red blood cell count (such as severe tiredness, pale lips/nails/skin, fast heartbeat/breathing with usual activities), swollen/painful tongue.
A very serious allergic reaction to this drug is rare. However, stop this medication immediately and seek immediate medical attention if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.
In the US -
Before taking pyrimethamine, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.
Before using this medication, tell your doctor or pharmacist your medical history, especially of: seizures, kidney problems, liver problems, a certain type of low red blood cell count (megaloblastic anemia due to low blood folate), low folic acid levels from other conditions (such as malnutrition, problems with absorption of food, alcoholism), low red/white blood cell counts, low blood-clotting cell (platelet) count.
Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).
During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor. Folic acid is very important during pregnancy. Your doctor will prescribe folic/folinic acid to prevent low folate levels.
The effects of some drugs can change if you take other drugs or herbal products at the same time. This can increase your risk for serious side effects or may cause your medications not to work correctly. These drug interactions are possible, but do not always occur. Your doctor or pharmacist can often prevent or manage interactions by changing how you use your medications or by close monitoring.
To help your doctor and pharmacist give you the best care, be sure to tell your doctor and pharmacist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products) before starting treatment with this product. While using this product, do not start, stop, or change the dosage of any other medicines you are using without your doctor's approval.
Some products that may interact with this drug include: lorazepam, penicillamine, sulfa drugs (such as sulfamethoxazole), drugs that can lower folate levels (such as phenytoin, trimethoprim), drugs that can lower blood counts (such as proguanil, zidovudine, chemotherapy including methotrexate, daunorubicin, cytosine).
This document does not contain all possible drug interactions. Keep a list of all the products you use. Share this list with your doctor and pharmacist to lessen your risk for serious medication problems.
If overdose is suspected, contact a poison control center or emergency room immediately. US residents can call their local poison control center at 1-800-222-1222. Canada residents can call a provincial poison control center. Symptoms of overdose may include: abdominal pain, severe/repeated vomiting, vomiting blood, seizures, slow/shallow breathing, inability to wake up.
Do not share this medication with others.
Laboratory and/or medical tests (such as complete blood count, liver blood tests) should be performed periodically to monitor your progress or check for side effects. Consult your doctor for more details.
If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose and resume your usual dosing schedule. Do not double the dose to catch up.
Store at room temperature between 59-77 degrees F (15-25 degrees C) away from light and moisture. Do not store in the bathroom. Keep all medicines away from children and pets.
Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company for more details about how to safely discard your product.
Information last revised March 2013. Copyright(c) 2013 First Databank, Inc.
With WebMD's Medicine Cabinet, you can check interactions with drugs.Go to medicine cabinet