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Table 3 Drugs that interact with pyrimethamine

From: Combination of probenecid-sulphadoxine-pyrimethamine for intermittent preventive treatment in pregnancy

Drug

Effect of Interaction

Gold salts

Increased risk of blood dyscrasias

Methotrexate

Increased risk of bone marrow suppression

Dapsone

Folate antagonists may increase the likelihood of adverse hematologic reactions (e.g., agranulocytosis, anaemia)

Carvedilol

Possible for increased serum concentration of the S-carvedilol enantiomer

Phenothiazines

Anti-malarial agents may increase the serum concentration

Fesoterodine

Serum concentrations of the active metabolite may be increased

Nebivolol

Serum concentration may be increased

Zidovudine, abacavir, lamivudine

Increased risk of bone marrow suppression

Tamoxifen

Metabolism of Tamoxifen to the active metabolites may be decreased

Lorazepam

Increases risk of elevated liver function tests

Codeine

CYP2D6 inhibitors may prevent the metabolic conversion of codeine to its active metabolite morphine, diminishing its therapeutic effect

Tramadol

CYP2D6 inhibitors may prevent the metabolic conversion to the active metabolite, diminishing its therapeutic effect

Antacids

Reduce the absorption of pyrimethamine (decreased bioavailability)