Generic name: pyrimethamine (pir-i-METH-a-meen)
Drug class: Miscellaneous antimalarials
Medically reviewed by Drugs.com. Last updated on Jul 12, 2021.
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 used together with a sulfonamide (eg, sulfadoxine) to treat toxoplasmosis. It belongs to a group of medicines called antiprotozoals. It works by killing or preventing the growth of a parasite called Toxoplasma gondii.
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.
Appropriate studies performed to date have not demonstrated pediatric-specific problems that would limit the usefulness of pyrimethamine in the pediatric population. Safety and efficacy have been established.
Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of pyrimethamine in the elderly. However, elderly patients are more likely to have age-related liver, kidney, or heart problems, which may require caution and an adjustment in the dose for patients receiving pyrimethamine.
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:
- Alcohol abuse or dependence or
- Malabsorption syndrome (trouble absorbing food)—Use with caution. May cause side effects to become worse.
- Folate deficiency or
- Kidney disease or
- Liver disease or
- Seizures—Use with caution. May make these conditions worse.
- Megaloblastic anemia caused by folate deficiency—Should not be used in patients with this condition.
Proper use of pyrimethamine
Take pyrimethamine only as directed by your doctor. Do not take more of it, do not take it more often, and do not take it for a longer time than your doctor ordered.
It is best to take pyrimethamine with food to help prevent vomiting and loss of appetite.
Pyrimethamine is usually given with folinic acid to help prevent blood problems. If you are using a combination of medicines, it is important that you take each medicine at the right time. Follow your doctor's instructions on when to take these medicines.
Take all of the medicine in your prescription to clear up your infection, even if you feel better after the first few doses.
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 oral dosage form (tablets):
- For treatment of toxoplasmosis:
- Adults—At first, 50 to 75 milligrams (mg) of pyrimethamine together with 1 to 4 grams (g) of sulfonamide once a day for 1 to 3 weeks. Your doctor may adjust your dose as needed and tolerated.
- Children—Dose is based on body weight and must be determined by your doctor. The starting dose is usually 1 milligram (mg) per kilogram (kg) of body weight per day, given in 2 divided doses. Your doctor may adjust the dose as needed and tolerated.
- For treatment of toxoplasmosis:
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.
Ask your healthcare professional how you should dispose of any medicine you do not use.
Precautions while using pyrimethamine
It is very important that your doctor check your or your child's progress at regular visits to make sure that pyrimethamine is working properly. Blood tests are needed to check for unwanted effects.
If your symptoms do not improve within a few days or if they become worse, check with your doctor.
Pyrimethamine may decrease the amount of folate in the body. Tell your doctor if you have burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings, changes in vision, confusion, depression, redness or soreness of the tongue, ulcers inside the mouth, unusual tiredness or weakness.
Do not drink alcohol while you are using pyrimethamine.
Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.
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:
- Chest pain
- dry cough
- rapid or trouble breathing
- skin rash
- unusual tiredness or weakness
Incidence not known
- Black, tarry stools
- bleeding gums
- blistering, peeling, or loosening of the skin
- blood in the urine or stools
- difficulty swallowing
- fainting spells
- fast or irregular heartbeat
- hives, itching
- irritation or soreness of the tongue
- joint or muscle pain
- lower back or side pain
- puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
- painful or difficult urination
- pale skin
- pinpoint red spots on the skin
- red, irritated eyes
- red skin lesions, often with a purple center
- sore throat
- sores, ulcers, or white spots on the lips or in the mouth
- swollen glands
- tightness in the chest
- unusual bleeding or bruising
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:
Incidence not known
- Loss of appetite
- weight loss
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.
More about pyrimethamine
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- During Pregnancy or Breastfeeding
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