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    Folate synthesis inhibitors

    Folate synthesis inhibitors proguanil and pyrimethamine act similar in protozoa as trimethoprim in bacteria: they inhibit the enzyme dihydrofolate reductase. Without folic acid the parasite cannot synthesize nucleic acids.

    Pyrimethamine is usually given in combination with a sulphonamide to enhance folate synthesis inhibition. This combination can treat malaria and toxoplasmosis.

    Pyrimethamine has low toxicity when applied in low doses. Rash is a side effect; in high doses folate deficiency can occur, causing depression of haematopoiesis. In high doses it can have teratogenic effects.

    1

    A sulfonamide is combined with pyrimethamine to produce an antimalarial action by sequential blockade of folate synthesis in sensitive Plasmodium strains.

    2

    Co-treatment with proguanil and pyrimethamine is preferred since cross-resistance can easily develop when used separately. 

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