Pyrimethamine has also been used to treat diarrhea caused by various parasitic infections. Most of these side effects are caused by the tendency of pyrimethamine to leach folic acid from the body.
Folic acid is an essential nutrient vital to the production of red blood cells.
Loss of folic acid over time can result in more serious consequences to the human body, including a progressive anemia and even permanent organ damage. The use of some form of folic acid replacement therapy is vitally necessary for anyone using this drug over an extended period of time. Pyrimethamine usually comes in 25mg oral tablets. For the treatment of toxoplasmosis, the usual dose is one 25 mg tablet daily. Glaxo-Wellcome has an HIV Patient Assistance Program for this drug.