Trimethoprim sulphamethoxazole therapy and folate nutrition

Treatment of infection with the drug combination of trimethoprim sulphamethoxazole (TMP S) in the recommended dose did not result in adverse haematological effects in patients with normal folate nutrition. TMP S given to patients with suboptimal folate stores sometimes resulted in the appearance or aggravation of both morphological and biochemical indices of folate depletion, although over a period of 10 days there were no significant alterations in the haemoglobin levels or platelet counts. It is suggested that if treatment with TMP S in 'at risk' patients is necessary over prolonged periods, then haematological indices and tests of folate status should be checked at regular intervals.