Pyrimethamine (Oral)

Pyrimethamine is frequently used as a treatment for toxoplasmosis, an infection of parasites within the body.


Pyrimethamine is used to treat a number of conditions, and generic forms may be cheaper and more available. If you require this medication or think that you may need treatment with this drug, talk to your doctor to receive a prescription.

This drug is often prescribed in tandem with other drugs to increase its efficiency. Talk to your doctor about which medications are safe to use with this drug, and do not take this medication with anything that may interact with it. This medication comes primarily in tablet form, and should only be taken orally. Use this drug responsibly, and only take it as directed. In cases of overdose, contact emergency medical services right away.

Pyrimethamine may cause side effects, including gastrointestinal problems like nausea and vomiting. These side effects are normal, but contact your doctor if they persist or worsen. Allergic reactions have been recorded, although they are rare. Stop taking this medication if you experience allergy symptoms such as trouble breathing, rash and unexplained fever.

This drug comes with risks. Do not take this drug if you have a history of blood problems, issues with your liver, low folic acid levels and kidney problems. Alcoholics or people with a history of alcohol abuse should be cautious when taking this medication and only do so with a doctor's supervision. Pregnant and nursing mothers should speak to their doctor before using this medication, as it may cause complications with the child.

Most can take this drug with no complications. Speak to your doctor if you think you may need a Pyrimethamine prescription.

Conditions Treated

  • Infection of protozoal parasites
  • Prevention of Malaria (previously)
  • Treatment of Toxoplasmosis
  • Treatment of cystoisosporiasi
  • Other assorted medical uses

Type of Medicine

  • Antiprotozoal medication
  • Antiparasite medication

Side Effects

This drug can come with side effects, most notably digestive issues. These side effects are often mild at best and should be ignored or treated with non-interactive medications. If they persist or worsen, speak to your doctor but do not stop your treatment. Your doctor is prescribing this medication because you need it, the benefits of taking the drug outweigh any potential discomfort. Potential, harmless side effects include:

  • Nausea and vomiting
  • Loss of appetite
  • Diarrhea

These side effects should be mild, and they do not warrant medical attention. If they persist, worsen or become serious, contact your doctor and schedule an appointment as soon as possible. Otherwise, stay hydrated and keep an eye on your condition.

However, this drug may have adverse effects on certain people. Stay cautious when using this drug, contact your doctor if you experience serious side effects. These side effects may be a symptom of a larger problem or a sign that Pyrimethamine is not right for you. Stop taking the medication and contact your doctor if you experience:

  • Unusual bruising or bleeding
  • Blood in urine or stools
  • Pain in the lower back and side
  • Glossitis, or pain and irritation of the tongue
  • Red spots on the skin
  • Flu-like symptoms (fever, chills, cough, and hoarseness)
  • Black/tarry stools

These side effects should not be ignored. If they occur, stop taking Pyrimethamine immediately and schedule an appointment with your doctor. This list is not exhaustive. If you experience any other painful, unexplained, or troubling side effects, talk to your doctor. Medical emergencies should be handled accordingly: if you think your life is in danger, contact medical help right away.

Pyrimethamine may cause allergies in people who have never taken it before. While rare, allergies to medication should be taken seriously. You may be more likely to experience allergies if you are taking this medication in tandem with a sulfa drug. Stop taking Pyrimethamine and contact your doctor if you experience:

  • Swelling of the tongue/face/lips
  • Unexplained fever
  • Trouble breathing
  • Rash

If your airways begin to close or you feel that your life is in danger, contact paramedics immediately and receive medical attention. Only take this drug with doctor approval, and discuss any allergies to Pyrimethamine or sulfa drugs before beginning your prescription.


Dosage can vary on age, condition, the severity of your condition and the drugs you are taking alongside Pyrimethamine. Do not take Pyrimethamine without a doctor's approval, and do not take more than recommended. Even if you believe it is safe, you should not take dosage into your own hands. There are likely reasons that your doctor prescribed the dosage they did.

The recommended doses may change depending on what condition Pyrimethamine is being used to treat. Here are a few of the most common dosages, but these can change depending on the patient. Use this guide only for comparison.

Adult dose for the prevention of Malaria: 25mg weekly for 6-10 weeks following exposure.

Pediatric dose for the prevention of Malaria: Should be determined by the doctor, but children over the ages of four are usually prescribed up to 12.5mg per week. Children under four should only take this drug with a doctor's explicit permission, and they should be monitored closely. Dosages up to 6.25mg are usual for young children.

Adult dose for the treatment of Malaria: 25mg daily, combined with a daily dose of sulfonamide.

Pediatric dose for the treatment of Malaria: Exact dosage is determined by body weight. Speak to your doctor for more information.

Adult dose for the treatment of Toxoplasmosis: 50-70mg daily, used in tandem with other medications. After 1-3 weeks, your doctor may adjust your dose.

Pediatric dose for the treatment of Toxoplasmosis: Exact dosage is determined by age, body weight, and additional medication. Talk to your doctor, only give this drug as directed.

Pyrimethamine is only available as an oral drug, and you should not take it any other way. Use this drug responsibly, and never give it to children without doctor approval. Only use as directed, do not take more or less than prescribed. Taking less than your recommended dose may cause the medication to be less effective and even detrimental. Taking more may result in overdose.

Symptoms of overdose include:

  • Severe stomach or abdominal pain
  • Seizures or convulsions
  • Persistent vomiting
  • Excitability

Contact poison control or medical help if an overdose is suspected. Make sure to find the prescription bottle and present it, and be prepared to give an estimate on how much the afflicted person took. Be cautious when taking and storing this medication, and make sure to handle this drug responsibly.


This drug may interact with other prescription or over-the-counter drugs. Make sure to give your doctor an extended list of all your medications to avoid any possible interactions. Some interactions can be mild and cause nothing more than discomfort, but others can be severe, even fatal. Keep your doctor in the loop, and be sure to inform them before you begin any new medications during your Pyrimethamine prescription. Common interactions for this drug include:

  • Antibiotics like penicillamine
  • Benzodiazapines like lorazepam
  • Any medications containing gold or gold sodium.
  • Deferiprone
  • Drugs that lower blood counts
  • Chemotherapy drugs
  • Drugs that lower folate levels
  • Live cholera vaccine

Your doctor may prescribe some of these drugs together if the interaction is mild. Otherwise, they may choose to lower your dose for one or both drugs, change your prescription, or put you on a different treatment entirely. Only your doctor can determine what is safe for you personally, so do not try to pick medications yourself.

Be cautious while taking any of these medications together, report any unusual changes in your health to your doctor. Stop taking one or both medications if you experience pain, serious side effects or other troubling symptoms.

Avoid drinking while on this drug, as it may cause complications in your treatment. Only use this drug as directed; you are personally responsible for your own health when you take prescription medications. A failure to follow your doctor's orders may result in unwanted side effects, complications and serious medical issues.


This drug may come with risks, especially if you suffer from additional conditions. You should only take this drug if you are sure that it is safe to do so, so talk to your doctor about your current condition before deciding on a treatment. While some risks are necessary for your overall health, you should keep an eye on your health if you suffer from the following conditions:

  • Blood problems such as anemia. High dosages of Pyrimethamine may worsen these conditions.
  • Seizure disorders, including epilepsy. High dosages may cause convulsions and increase the likelihood of a seizure.
  • Malnutrition. This condition causes low levels of Vitamin B, which may increase risks.
  • Alcoholism. This condition also causes low levels of Vitamin B, which may increase risks.
  • Kidney problems. Problems with the kidney may affect how well your body filters out this medication. A failure to expel this drug may result in build-up and increased side effects.
  • Liver problems.
  • An allergy to Pyrimethamine, or the inactive ingredients within the pill. Stop taking the medication and talk to your doctor if you experience allergy symptoms.

This drug can be used on children, but only in specific and closely monitored situations. Pregnant women should speak to their doctor before beginning any Pryimethamine prescription. This drug has not been shown to harm infants during breastfeeding, but if you have concerns about the safety of your child, speak to your doctor or switch to formula.

This drug should always be taken with a doctor's supervision to avoid complications or danger to the patient. Handle this medication responsibly, and do not take it off-prescription. Even if you think you may require the medication, there are other factors to consider before seeking treatment. Always speak to a doctor about beginning a new prescription, and follow their orders regarding dosage and treatment.


This drug should be kept in a cool, dry location. Store at room temperature, and keep this drug protected from light. Exposure to light, heat and water may reduce the efficacy of this medication and affect your treatment. Do not take medication that may have been ruined or exposed to these elements. Take this drug with meals, but try to avoid crushing or cutting the pills unless absolutely necessary.

Do not keep excess amounts of this drug. It is a powerful anti-parasitic drug, it should never be taken randomly or without cause. If you have leftover medication, dispose of it in its original prescription bottle or seal the pills within a bag. Throw it away with your normal garbage in an opaque bag. Do not keep extra medication after your prescription has ended. This drug can expire and taking this drug after its expiration date can be harmful to your health.

Do not leave this medication where pets or children can get it. Store it in a locked bottle out of reach in a cabinet or drawer. If an overdose is suspected, contact poison control as soon as possible, try to give them an estimate on how much the afflicted person took and when. Make sure to give them all the information available on the drug, and give them the original bottle if possible.

Only store this drug in a safe location to avoid accidents. If you lose the medication, contact your pharmacist or doctor for a refill/new prescription. This drug should be taken on-time for the right effect. Do not miss doses if you can help it.


While it was previously used to prevent and treat malaria, this drug is not recommended due to widespread resistance to the drug. Pyrimethamine is used to treat a number of other conditions, including toxoplasmosis. When used as directed, it can be a powerful agent in clearing infection. This drug is often given in tandem with other medications to maximize its effect. Only take this drug with the recommended medications, and do not combine this drug with random antibiotics.

While it comes with side effects, this drug has a high success rate among patients. Allergies and adverse reactions should not be ruled out, but they are usually rare and can usually be predicted/prevented. The risks of this drug are far lower than those of the diseases treated by this medication. Side effects are usually mild at best, but if you experience troubling changes, talk to your doctor.

If your conditions persist or worsen during your treatment, or returns after your prescription has ended, speak to your doctor right away. Only take this drug as directed, and do not give this drug to anyone else. If you have concerns about how this drug works, how it may affect you, or the side effects/risks, talk to your doctor before taking your first dose. This drug is only available by prescription, so visit your doctor if you think you may require this medication.


Last Reviewed:
January 31, 2018
Last Updated:
January 27, 2018