A group of drugs that is used to treat infections caused by protozoa
Pyrimethamine with sulfadiazine
A range of drugs is used to treat infections caused by single-celled organisms called protozoa. Some antiprotozoals, such as metronidazole, are also used for bacterial infections. A specific group of these drugs is used to treat malaria, a serious disease caused by protozoa that affects millions of people worldwide (see Antimalarial drugs).
Antiprotozoals act in various ways; some of the drugs work by preventing protozoa from multiplying.
Antiprotozoals are commonly used to treat infections such as trichomoniasis and giardiasis. Metronidazole or tinidazole is often taken for these disorders. Another use for antiprotozoals, particularly pyrimethamine with sulfadazine, is to treat toxoplasmosis, an infection that can cause severe illness in fetuses and people with reduced immunity. Co-trimoxazole and pentamidine may be used for pneumocystis infection, a form of pneumonia that is potentially fatal in people whose immunity is reduced.
For minor infections, antiprotozoals are usually taken for about a week. Severe infections may need treatment for several months, especially in people with reduced immunity, such as those who have HIV infection or AIDS.
Most antiprotozoals are taken orally, but some may be injected to treat severe infections. Pentamidine is administered by injection or taken through an inhaler. This drug is given only under the supervision of a specialist.
Antiprotozoal drugs often cause side effects, including nausea, diarrhoea, and abdominal cramps. If you are taking metronidazole, you should avoid alcohol because it can cause vomiting. Another side effect of the drug is darkening of the urine. Pentamidine may cause a severe drop in blood pressure, either when it is administered or directly afterwards. In rare cases, pyrimethamine reduces red blood cell production, causing anaemia. If you have unusual bruising or bleeding while taking this drug, notify your doctor because these may be signs of a blood disorder.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.