Immune thrombocytopenia induced by cotrimoxazole.

Cotrimoxazole administration is occasionally associated with thrombocytopenia. Interference with folate metabolism has been postulated. The drug has also been postulated to induce an autoantibody by acting as a hapten, but proof has not been forthcoming. A case is reported in which the serum has been shown to contain an anti-platelet autoantibody requiring sulphamethoxazole or cotrimoxazole for activity.