Serious
pancytopenia and megaloblastic anaemia have been described in patients given
pyrimethamine and
co-trimoxazole.
Caution should be used in prescribing the combination, especially in the presence of other drugs (e.g. methotrexate, phenytoin) or disease states that may predispose to folate deficiency. Note that the manufacturer of sulfadoxine/pyrimethamine recommends that the concurrent use of
sulfonamides (including co-trimoxazole) should be avoided.