Pyrimethamine
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Drug Status
Government Approvals
US(FDA), UK(BNF)
WHO Essential Medicine
YES
Known Teratogen
Possible
Pharmaceutical Class
Dihydrofolate Reductase Inhibitor Antimalarial
Controlled Drug Substance
No
Pyrimethamine
Summary
Pyrimethamine is primarily used to treat toxoplasmosis, an infection caused by the Toxoplasma parasite. It is often used in combination with a sulfonamide for enhanced effectiveness.
Pyrimethamine works by inhibiting an enzyme called dihydrofolate reductase, which is crucial for folic acid metabolism in parasites. This prevents the parasites from synthesizing nucleic acids necessary for their growth and reproduction, effectively controlling the infection.
For adults, the usual daily dose of Pyrimethamine is 50 to 75 mg taken with a sulfonamide. For children, the dose is 1 mg/kg/day divided into two equal daily doses. This dose may be reduced by half after 2 to 4 days and continued for about a month.
Common side effects of Pyrimethamine include anorexia (decreased appetite) and vomiting. Serious adverse effects can include hypersensitivity reactions, megaloblastic anemia, leukopenia (low white blood cell count), and thrombocytopenia (low platelet count).
Pyrimethamine is contraindicated in patients with hypersensitivity to the drug or its components, and in those with megaloblastic anemia due to folate deficiency. It may be carcinogenic and should be kept out of children's reach due to overdose risks.
Indications and Purpose
How does Pyrimethamine work?
Pyrimethamine works by inhibiting the enzyme dihydrofolate reductase, which is crucial for folic acid metabolism in parasites. This inhibition prevents the parasites from synthesizing nucleic acids necessary for their growth and reproduction, effectively controlling the infection.
Is Pyrimethamine effective?
Pyrimethamine is an antiparasitic medication that works by inhibiting folic acid metabolism in parasites like Toxoplasma. Its effectiveness is enhanced when used with sulfonamides, as demonstrated in studies on experimental toxoplasmosis in mice and rabbits. Always consult a healthcare provider for personalized advice.
What is Pyrimethamine?
Pyrimethamine is an antiparasitic medication used primarily to treat toxoplasmosis, often in combination with a sulfonamide. It works by inhibiting folic acid metabolism in parasites, which is essential for their growth and reproduction. This action is highly selective against the parasites, making it effective in treating infections.
Directions for Use
For how long do I take Pyrimethamine?
Pyrimethamine is typically used for 1 to 3 weeks initially, depending on the patient's response and tolerance. The dosage may then be reduced and continued for an additional 4 to 5 weeks. Always follow your doctor's specific instructions.
How do I dispose of Pyrimethamine?
If you can, bring unused medicines to a drug take-back program or collection site at a pharmacy or hospital. They will dispose of this medicine properly so they don't harm people or the environment. If you can't find a take-back program, you can throw most medicines in the trash at home. But first, take them out of their original containers, mix them with something undesirable like used coffee grounds, seal the mixture in a plastic bag and throw it away.
How do I take Pyrimethamine?
Pyrimethamine can be taken with meals to minimize gastrointestinal side effects like vomiting. There are no specific food restrictions mentioned, but always follow your doctor's instructions and consult them for personalized advice.
How long does it take for Pyrimethamine to start working?
Pyrimethamine is well absorbed, with peak levels occurring between 2 to 6 hours after administration. However, the time it takes to notice an improvement in symptoms can vary. Always consult a healthcare provider for personalized advice.
How should I store Pyrimethamine?
Pyrimethamine should be stored at a temperature between 15° to 25°C (59° to 77°F) in a dry place and protected from light. Always keep it out of reach of children.
What is the usual dose of Pyrimethamine?
For adults, the usual daily dose of pyrimethamine is 50 to 75 mg, taken with a sulfonamide. For children, the dose is 1 mg/kg/day, divided into two equal daily doses. After 2 to 4 days, this dose may be reduced to half and continued for about a month. Always follow your doctor's specific instructions.
Warnings and Precautions
Can I take Pyrimethamine with other prescription drugs?
Pyrimethamine may interact with sulfonamides, quinine, and other antimalarials. It can increase the risk of bone marrow suppression when used with antifolic drugs or agents associated with myelosuppression, such as methotrexate. Mild hepatotoxicity has been reported with lorazepam. Always consult a healthcare provider for personalized advice.
Can Pyrimethamine be taken safely while breastfeeding?
Pyrimethamine is excreted in human milk, and due to potential serious adverse reactions in nursing infants, a decision should be made to either discontinue nursing or the drug. Always consult a healthcare provider for personalized advice.
Can Pyrimethamine be taken safely while pregnant?
Pyrimethamine should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. It has been shown to be teratogenic in animal studies. Concurrent administration of folinic acid is strongly recommended during pregnancy. Always consult a healthcare provider for personalized advice.
Does Pyrimethamine have adverse effects?
Adverse effects are unwanted or harmful effects caused by a medicine. Pyrimethamine can cause nausea, vomiting, and loss of appetite, which are common. Rare but serious effects include severe skin reactions, blood disorders, or liver problems. If you experience symptoms like a rash, unusual bleeding, or yellowing of the skin, seek medical help immediately. Always report new symptoms to your doctor and never stop taking the medicine without consulting them.
Does Pyrimethamine have any safety warnings?
Pyrimethamine comes with safety warnings. It can cause serious skin reactions, so watch for rashes or blisters. It may also affect blood cells, leading to symptoms like unusual bruising or fatigue. Liver problems are another risk, so look out for yellowing of the skin or eyes. If you notice any of these signs, seek medical help immediately. Always follow your doctor's advice and report any new symptoms.
Is it safe to drink alcohol while taking Pyrimethamine?
Most people tolerate Pyrimethamine well, and occasional alcoholic drinks should not affect the way this medicine works. There are no well-established interactions between Pyrimethamine and alcohol. However, it's always wise to consume alcohol in moderation and be aware of how your body reacts. If you experience any unusual symptoms, consult your healthcare provider.
Is it safe to exercise while taking Pyrimethamine?
Most people tolerate Pyrimethamine well, and it should not limit your ability to exercise. There are no known symptoms caused by this medicine that would affect exercise capacity, physical strength, or endurance. However, if you experience any unusual symptoms during physical activity, such as dizziness or fatigue, take precautions and consult your healthcare provider.
Is it safe to stop Pyrimethamine?
Pyrimethamine is often used for treating infections, which are temporary conditions. Stopping it abruptly can lead to the infection not being fully treated, which might cause it to return or worsen. There are no known withdrawal symptoms, but stopping without medical advice can lead to complications. Always consult your doctor before stopping Pyrimethamine to ensure it's safe and appropriate for your situation.
Is Pyrimethamine addictive?
Pyrimethamine is not known to be addictive. It does not have habit-forming potential, so there's no risk of physical or psychological dependence. You can take it as prescribed without worrying about addiction. Always follow your healthcare provider's instructions and report any concerns you may have.
Is Pyrimethamine safe for the elderly?
For elderly patients, dose selection should be cautious, usually starting at the low end of the dosing range. This is due to the greater frequency of decreased hepatic, renal, or cardiac function, and the presence of other diseases or drug therapies. Always consult a healthcare provider for personalized advice.
What are the most common side effects of Pyrimethamine?
A side effect is an unwanted reaction to a medicine. Common side effects of Pyrimethamine include nausea, vomiting, loss of appetite, headache, and dizziness. These effects are usually mild and may go away as your body adjusts. It's important to remember that new symptoms can occur with any new medicine and might not be related to the drug. Always talk to your healthcare provider before stopping any medication.
Who should avoid taking Pyrimethamine?
Pyrimethamine is contraindicated in patients with hypersensitivity to the drug or its components, and in those with megaloblastic anemia due to folate deficiency. It has a narrow therapeutic window, and folate deficiency signs require dosage adjustment or discontinuation. It may be carcinogenic and should be kept out of children's reach due to overdose risks. Always consult a healthcare provider for personalized advice.
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