Generic Name: pyrimethamine (pir-i-METH-a-meen)
Medically reviewed by Drugs.com. Last updated on Oct 8, 2020.
Commonly used brand name(s)
In the U.S.
Available Dosage Forms:
Therapeutic Class: Antimalarial
Pharmacologic Class: Folic Acid Antagonist
Uses for pyrimethamine
Pyrimethamine is an antiprotozoal medicine. Antiprotozoals work by killing protozoa (tiny, one-celled animals) or preventing their growth. Some protozoa are parasites that can cause many different kinds of infections in the body.
Pyrimethamine is used with one or more other medicines to treat and prevent malaria and to treat toxoplasmosis. Pyrimethamine may also be used for other problems as determined by your doctor.
Pyrimethamine is available only with your doctor's prescription.
Before using pyrimethamine
In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For pyrimethamine, the following should be considered:
Tell your doctor if you have ever had any unusual or allergic reaction to pyrimethamine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.
Pyrimethamine has been used in children and, in effective doses, has not been shown to cause different side effects or problems in children than it does in adults.
Many medicines have not been studied specifically in older people. Therefore, it may not be known whether they work exactly the same way they do in younger adults or if they cause different side effects or problems in older people. There is no specific information comparing use of pyrimethamine in the elderly with use in other age groups.
There are no adequate studies in women for determining infant risk when using this medication during breastfeeding. Weigh the potential benefits against the potential risks before taking this medication while breastfeeding.
Interactions with medicines
Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking pyrimethamine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using pyrimethamine with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.
Using pyrimethamine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Cholera Vaccine, Live
Using pyrimethamine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
Interactions with food/tobacco/alcohol
Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.
Other medical problems
The presence of other medical problems may affect the use of pyrimethamine. Make sure you tell your doctor if you have any other medical problems, especially:
- Allergy to pyrimethamine or any ingredient in the medicine—pyrimethamine should not be used
- Anemia or other blood problems—High doses of pyrimethamine may make these conditions worse
- Kidney problems or
- Liver problems or
- Lack of vitamin B in the body caused by
- Alcoholism (drinking too much alcohol) or
- Malabsorption syndrome (when a person's body does not absorb enough nutrients from the food they eat)
- Seizure disorders, such as epilepsy—High doses of pyrimethamine may increase the chance of convulsions (seizures)
Proper use of pyrimethamine
Keep pyrimethamine out of the reach of children. Overdose is especially dangerous in children.
If pyrimethamine upsets your stomach or causes vomiting, it may be taken with meals or a snack.
If you are taking pyrimethamine to treat malaria, take the number of tablets your doctor told you to take (up to 3) once, as a single dose, along with other medicine your doctor gave you. If you develop a fever and are not near a medical facility, and are taking pyrimethamine to treat what you think may possibly be malaria, take the number of tablets your doctor told you to take (up to 3) once, as a single dose.
Pyrimethamine works best when you take it on a regular schedule. If you are to take two doses a day, one dose may be taken with breakfast and the other one with the evening meal. Make sure that you do not miss any doses. If you have any questions about this, check with your health care professional.
The dose of pyrimethamine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of pyrimethamine. If your dose is different, do not change it unless your doctor tells you to do so.
The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.
- For the treatment of malaria:
- Adults and adolescents: 25 milligrams of pyrimethamine daily together with a sulfonamide for 2 days. These two medicines may also be taken with other medicine. This will be determined by your doctor.
- Children: Dose is based on body weight and will be determined by the doctor. Pyrimethamine may be taken together with other medicines.
- For the treatment of toxoplasmosis:
- Adults and adolescents: Starting dose if 50 to 75 milligrams of pyrimethamine daily taken together with other medicines for several weeks. After one to three weeks, your doctor may lower your dose. The proper dose for you must be determined by the doctor.
- Children: Dose is based on body weight and must be determined by the doctor.
- For the prevention of malaria:
- Adults and adolescents: 25 milligrams taken once a week.
- Children: Dose is based on age and must be determined by the doctor.
If you miss a dose of pyrimethamine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.
Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.
Keep out of the reach of children.
Do not keep outdated medicine or medicine no longer needed.
Precautions while using pyrimethamine
It is very important that your doctor check you at regular visits for any blood problems that may be caused by pyrimethamine, especially if you will be taking pyrimethamine in high doses for toxoplasmosis.
If your symptoms do not improve within a few days or if they become worse, check with your doctor.
If pyrimethamine causes anemia, your doctor may want you to take leucovorin (e.g., folinic acid, Wellcovorin) to help clear up the anemia. If so, it is important to take the leucovorin every day while you are taking pyrimethamine. Do not miss any doses.
Pyrimethamine, especially in high doses, may cause blood problems. These problems may result in a greater chance of certain infections, slow healing, and bleeding of the gums. Therefore, you should be careful when using regular toothbrushes, dental floss, and toothpicks. Dental work should be delayed until your blood counts have returned to normal. Check with your medical doctor or dentist if you have any questions about proper oral hygiene (mouth care) during treatment.
Pyrimethamine side effects
Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.
Check with your doctor immediately if any of the following side effects occur:
- Black, tarry stools
- blood in urine or stools
- cough or hoarseness
- fever or chills
- irritation or soreness of tongue
- lower back or side pain
- painful or difficult urination
- pinpoint red spots on skin
- unusual bleeding or bruising
- Bleeding or crusting sores on lips
- chest pain or discomfort
- muscle cramps or pain
- redness, blistering, peeling, or loosening of skin
- skin rash
- sores, ulcers, and/or white spots in mouth
- sore throat
- unusual tiredness or weakness
Frequency not known
- Blood in urine
- difficulty swallowing
- fainting spells
- fast, slow, or irregular heartbeat
- joint or muscle pain
- pale skin
- pounding or rapid pulse
- puffiness or swelling of the eyelids or around the eyes, face, lips or tongue
- rapid breathing
- red, irritated eyes
- red skin lesions, often with a purple center
- shortness of breath
- swollen glands
- tightness in chest
- unexplained bleeding or bruising
Symptoms of overdose
- Abdominal or stomach pain
- convulsions (seizures)
- increased excitability
- vomiting (severe and continuing)
Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:
- loss of appetite
Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.
Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
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- Drug class: miscellaneous antimalarials
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