BMA Concise Guide to Medicine & Drugs

Pyrimethamine

Brand name Daraprim

Used in the following combined preparation Fansidar

QUICK REFERENCE

Drug group Antiprotozoal drug and antimalarial drug

Overdose danger rating Medium

Dependence rating Low

Prescription needed Yes

Available as generic No

GENERAL INFORMATION

Pyrimethamine is a drug used to treat protozoal infections, which include malaria. Because malaria parasites can readily develop resistance to pyrimethamine, the drug is now always given combined with the antibacterial drug sulfadoxine (Fansidar) for the treatment of malaria. The activity of the combination greatly exceeds that of either drug alone. Fansidar is used with quinine in the treatment of malaria. Pyrimethamine is not used for the prevention of malaria. Pyrimethamine is sometimes given with another drug, sulfadiazine, to treat toxoplasmosis in people with lowered immunity. Such treatment must be supervised by an expert.

Blood disorders can sometimes arise during prolonged treatment with pyrimethamine, and, because of this, blood counts are monitored regularly and vitamin supplements are given.

INFORMATION FOR USERS

Your drug prescription is tailored for you. Do not alter dosage without checking with your doctor.

How taken/used Tablets.

Frequency and timing of doses Once only, daily, or weekly, depending on condition being treated.

Dosage range Adults Depends on condition being treated. Children Reduced dose necessary according to age.

Onset of effect 24 hours.

Duration of action Up to 1 week.

Diet advice None.

Storage Keep in original container at room temperature out of the reach of children. Protect from light.

Missed dose If you are being treated for toxoplasmosis, take as soon as you remember. If your next dose is due within 24 hours, take a single dose now and alter the dosing day so that your next dose is one week later.

Stopping the drug Do not stop taking the drug without discussing it with your doctor.

Exceeding the dose An occasional unintentional extra dose is unlikely to cause problems. Large overdoses may cause trembling, breathing difficulty, seizures, blood disorders, and vomiting. Notify your doctor.

POSSIBLE ADVERSE EFFECTS

Pyrimethamine may cause a variety of adverse effects, including headache, loss of appetite, insomnia, stomach irritation, and a rash. Discuss with your doctor if headache, loss of appetite or insomnia are severe, or if stomach irritation or a rash develop. Unusual bleeding, bruising, tiredness, weakness, or a sore throat may be signs of a blood disorder and you should notify your doctor promptly if they occur. Breathing problems, fever, or signs of a chest infection should be reported to your doctor immediately.

INTERACTIONS

General note Drugs that suppress the bone marrow or cause folic acid deficiency may increase the risk of serious blood disorders when taken with pyrimethamine. Such drugs include anticancer and antirheumatic drugs, sulfasalazine, methotrexate, co-trimoxazole, trimethoprim, phenytoin, and phenylbutazone.

Lorazepam may cause liver damage when taken with pyrimethamine.

SPECIAL PRECAUTIONS

Be sure to tell your doctor if:

· You have long-term liver or kidney problems.

· You have had epileptic seizures.

· You have anaemia.

· You are allergic to sulphonamides.

· You have glucose-6-phosphate dehydrogenase (G6PD) deficiency.

· You are taking other medicines.

Pregnancy Pyrimethamine may cause folic acid deficiency in the unborn baby. Pregnant women receiving this drug should take a folic acid supplement. Discuss with your doctor.

Breast-feeding The drug passes into the breast milk, but at normal doses adverse effects on the baby are unlikely. Discuss with your doctor.

Infants and children Reduced dose necessary.

Over 60 No special problems.

Driving and hazardous work No special problems.

Alcohol No known problems.

Sunlight and sunbeds Avoid excessive exposure to sunlight.

PROLONGED USE

Prolonged use may cause folic acid deficiency, leading to serious blood disorders. Folic acid supplements may be recommended (in the form of folinic acid).

Monitoring Regular blood cell counts are required during high-dose or long-term treatment.