Agranulocytosis associated with chronic oral administration of cloxacillin for suppression of staphylococcal osteomyelitis.

Oral cloxacillin was used for chronic suppression of a 59-year-old woman with staphylococcal osteomyelitis. She received 380.5 gm of cloxacillin over 263 consecutive days. Severe agranulocytosis followed, reverting rapidly to normal with cessation of drug. The absence of signs of an allergic reactions such as rash, fever, or eosinophilia suggests that cloxacillin, like other semisynthetic penicillins, may exert a direct bone marrow toxicity.