What it is used for
- Toxoplasmosis, usually combined with another medicine
- Some malaria treatment and prevention, usually in combination
- Prevention of toxoplasmosis in people with weakened immune systems
How it works
Pyrimethamine blocks an enzyme parasites need to make folate, a building block essential for them to grow and multiply. Without it the parasites cannot reproduce.
How it is taken
Taken as oral tablets, usually as part of a combination and often alongside a folate-type supplement (folinic acid) to protect the body's own cells. For toxoplasmosis it is taken over a longer course. Take it exactly as your doctor directs, including any protective supplement prescribed with it.
No doses here on purpose. The right strength and schedule depend on you — only a doctor or pharmacist should set them. Always follow your prescription and the label.
Common side effects
- Nausea
- Loss of appetite
- Stomach upset
- Headache
- Mild rash
- Changes in taste
Serious effects — get help
- Sore throat, fever, mouth ulcers, or unusual bruising/bleeding suggesting a drop in blood counts — seek urgent care
- Severe skin reactions with blistering or peeling — seek emergency care
- Severe allergic reaction such as facial swelling — seek emergency care
- Seizures or severe confusion — seek urgent care
If a reaction is severe — for example trouble breathing, swelling of the face or throat, or collapse — go to the nearest emergency room now or call your local emergency number. Do not wait for an online consultation.
Interactions to watch
- Other antifolate medicines such as methotrexate or co-trimoxazole (added blood-count risk)
- Some seizure medicines
- Medicines that affect the bone marrow
- Other antimalarials
Who should take care
- A protective folate supplement (folinic acid) is often prescribed alongside it to reduce blood-count effects
- Regular blood-count monitoring is usually needed
- Tell your clinician about anemia, blood disorders, or kidney/liver problems
- Inform your clinician if pregnant or breastfeeding
- Store securely away from children