Toxicity of co-trimoxazole in nutritional haematinic deficiency.

Introduction Co-trimoxazole is an antibacterial combination of trimethoprim and sulphamethoxazole which acts by sequentially blockading folate metabolism (Elion, Singer & Hitchings, 1954; Darrell, Garrod & Waterworth, 1968). Cases of haematological toxicity have been reported following its use in patients with initially normal haematological status (Kahn, Fein & Brodsky, 1968; Paulley, 1970; McPherson & Raik, 1970; Geddes et al., 1971; Jewkes, Edwards & Grant, 1970; Jenkins, Hughes & Hall, 1970; Hulme & Reeves, 1971) but only a few have been of such severity as to be clinically significant. Chanarin & England (1972) reported the use of co-trimoxazole in four patients with known megaloblastic anaemia due to vitamin B12 or folate deficiency. There was suppression of the reticulocyte response in all, pancytopenia in two and anaemia with neutropenia in a third. We report serious pancytopenia following the administration of cotrimoxazole to a patient with iron, folate and vitamin B12 deficiency.