Serious
pancytopenia and megaloblastic anaemia have been described in patients
given
pyrimethamine and either
co-trimoxazole (which contains sulfamethoxazole) or other
sulfonamides.
Pyrimethamine is usually given with a sulfonamide for
toxoplasmosis and malaria.
Nevertheless, caution should be used in prescribing the combination, especially in
the presence of other drugs (e.g. methotrexate) or disease states that may
predispose to folate deficiency. When high-dose
pyrimethamine is used for the
treatment of
toxoplasmosis, the manufacturer recommends that all patients should receive a folate supplement. Note that the manufacturer of sulfadoxine/pyrimethamine recommends that the concurrent use of
sulfonamides (including co-trimoxazole) should be avoided.