To the Editor.
—Several cases of leukopenia induced by penicillinase-resistant penicillins have been reported.1-3 Theories for understanding drug-induced leukopenia have included: hypersensitivity reactions, dose-dependent, nonimmunologic, inhibition of myeloid precursor cells in the bone marrow and autoimmune phenomena with leukocyte antibodies.1,4,5 Despite these hypotheses, the mechanism of the neutropenia still remains unclear. The leukopenia in these cases has always been rapidly reversible after discontinuation of the drug; rechallenge has never been attempted. We describe a patient with cloxacillin-induced leukopenia in whom maintenance of half the initial dose produced a return of leukocytes and neutrophils to the normal ranges.
Report of a Case.
—A 73-year-old man was admitted to the hospital with a diagnosis of staphylococcal vertebral osteomyelitis. After 19 days of treatment, receiving only intravenous cloxacillin sodium, 12 g/day, the total leukocyte count dropped to 2.3x109/L, the neutrophil count to 1.0 x 109/L, and the