Drug-induced agranulocytosis.

An unexpected precipitous fall in peripheral leucocyte count may occur during treatment of certain sensitised individuals with drugs usually well tolerated by most people. Three basic mechanisms for drug sensitivity have been found. One is characterised by sudden destruction of large numbers of leucocytes in peripheral blood by antibodies elicited in response to drug sensitivity. A prototype for this type of reaction is aminopyrine. A second mechanism involves the production of a lupus-like syndrome followed by leucopenia in response to sensitisation to drugs such as procainamide. A third type involves development of agranulocytosis following a latent period during which a sensitive patient is treated with large amounts of chlorpromazine. This type of reaction is associated with production of bone marrow insufficiency in a patient who is believed to have a limited proliferative potential of bone marrow cells, which limit compensatory bone marrow response during treatment with a drug (e.g. chlorpromazine) that has limited bone marrow toxicity.