In the U.S.—

In Canada—

• Antiprotozoal

Pyrimethamine ( peer-i-METH-a-meen) is an antiprotozoal (AN-tee-proe-toe-ZOE-al) 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.

This medicine is used with one or more other medicines to treat and prevent malaria and to treat toxoplasmosis ( tok-soe-plaz-MOE-sis) . This medicine may also be used for other problems as determined by your doctor.

Pyrimethamine is available only with your doctor's prescription, in the following dosage form:

Oral
• Tablets (U.S. and Canada)

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:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to pyrimethamine. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy—Pyrimethamine has not been studied in pregnant women. However, studies in animals have shown that pyrimethamine causes birth defects such as cleft palate, brachygnathia (abnormal shortness of the jaw bone), oligodactyly (fewer than 5 digits on a hand or foot), microphthalmia (abnormal smallness of the eye). Before taking this medicine, make sure your doctor knows if you are pregnant or if you may become pregnant.

Breast-feeding—Pyrimethamine passes into breast milk. However, problems in nursing babies have not been reported. Mothers who are taking this medicine and who wish to breast-feed should discuss this with their doctor.

Children—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.

Older 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.

Other 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 health care professional know if you are taking any of the following:

• Amphotericin B by injection (e.g., Fungizone) or
• Antineoplastics (cancer medicine) or
• Antithyroid agents (medicine for overactive thyroid) or
• Azathioprine (e.g., Imuran) or
• Chloramphenicol (e.g., Chloromycetin) or
• Colchicine or
• Cyclophosphamide (e.g., Cytoxan) or
• Flucytosine (e.g., Ancobon) or
• Ganciclovir (e.g., Cytovene) or
• Interferon (e.g., Intron A, Roferon-A) or
• Mercaptopurine (e.g., Purinethol) or
• Methotrexate (e.g., Mexate) or
• Plicamycin (e.g., Mithracin) or
• Zidovudine (e.g., AZT, Retrovir)—Use of these medicines together with pyrimethamine may increase the chance of side effects affecting the blood

• Bone marrow suppressants (methotrexate [e.g., Rheumatrex], proguanil [e.g., Malarone], sulfonamides [medicines used to treat infections], trimethoprim-sulfamethoxazole [e.g., Bactrim], zidovudine [e.g., Retrovir])—may increase risk of bone marrow problems

• Lorazepam (e.g., Ativan)—Mild liver problems have been reported when using this medicine together with pyrimethamine

• Phenytoin (e.g., Dilantin)—Use of this medicine together with pyrimethamine may affect folate (vitamin B) levels in the body

• 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)
  —May make the condition worse

• Seizure disorders, such as epilepsy—High doses of pyrimethamine may increase the chance of convulsions (seizures)

Keep this medicine out of the reach of children. Overdose is especially dangerous in children.

If this medicine upsets your stomach or causes vomiting, it may be taken with meals or a snack.

If you are taking this medicine 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 this medicine 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.

This medicine 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.

Dosing—

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 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 taking pyrimethamine.

• 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.

Missed dose—

If you do miss a dose of this medicine, take it as soon as possible. This will help you to keep taking your medicine on a regular schedule. 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.

Storage—

To store this medicine:

• Keep out of the reach of children. Overdose is very dangerous.
• Store away from heat and direct light.
• Do not store in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

It is very important that your doctor check you at regular visits for any blood problems that may be caused by this medicine, especially if you will be taking this medicine 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 this medicine 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 this medicine. 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.

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:

• Less common
  • 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 
  
  

• Rare
  • 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;  diarrhea;  difficulty swallowing;  dizziness;  fainting spells;  fast, slow, or irregular heartbeat;  hives;  itching ;  joint or muscle pain;  lightheadedness;  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;  wheezing 
  
  

• Symptoms of overdose
  • Abdominal or stomach pain;  convulsions (seizures);  increased excitability;  vomiting (severe and continuing) 
  
  

Other 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. However, check with your doctor if any of the following side effects continue or are bothersome:

• Less common
  • Diarrhea;  loss of appetite;  nausea;  vomiting 
  
  

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.

Once a medicine has been approved for marketing for a certain use, experience may show that it is also useful for other medical problems. Although these uses are not included in product labeling, pyrimethamine is used in certain patients with the following medical conditions:

• Isosporiasis (treatment and prevention)
• Pneumocystis carinii pneumonia (treatment)

For patients taking this medicine for Pneumocystis carinii pneumonia:

• Pyrimethamine is used in combination with other medicines for mild to moderate pneumonia in patients who cannot take standard treatment.

Other than the above information, there is no additional information relating to proper use, precautions, or side effects for these uses.