Hematologic abnormalities after oral trimethoprim-sulfamethoxazole therapy in children.

The development of hematologic abnormalities was prospectively evaluated in 50 children treated for ten days each with oral trimethoprim-sulfamethoxazole and compared with a control group of 20 children with similar infections treated with amoxicillin trihydrate. Neutropenia (polymorphonuclear neutrophilic leukocyte counts, less than or equal to 1,500/cu mm) developed in 17 (34%) of the 50 children treated with trimethoprim-sulfamethoxazole compared with one (5%) in the control group of 20 children (P less than 0.001). Thrombocytopenia (platelet count, less than 150,000/cu mm) developed in six (12%) of the children treated with trimethoprim-sulfamethoxazole, but it did not develop in any of the amoxicillin-treated children (P less than .01). Neutropenia occurred mostly during the first week of treatment and lasted a mean of 8.9 days. Thrombocytopenia was noted between the seventh and 16th day (mean, 10.3 days) and lasted a mean of 12.7 days. Both side effects resolved spontaneously without ill effects. Children treated with oral trimethoprim-sulfamethoxazole should be followed up with biweekly leukocyte and platelet counts, and treatment should be discontinued if severe neutropenia or thrombocytopenia develops.