Abstract

The practice of performing regular blood counts during therapy with drugs known to cause dyscrasias has varied over the years. For a time they were thought essential during treatment with drugs like thiouracil and phenylbutazone, but they were abandoned when it was realised that blood changes can develop so quickly that a normal count might give only a false sense of security. It seemed better to take a preliminary count to exclude prior abnormality and to warn patients to stop the drug and report at once if they developed symptoms such as sore throat or mouth ulceration, so that a count could be done and the treatment changed if necessary. However, this approach is not satisfactory when either gold or cytotoxic drugs are used because potentially fatal irreversible aplasia may occur before symptoms are noticed. Recent advances in knowledge of the mechanisms of drug-induced blood dyscrasias¹ allow a more rational approach to their detection and avoidance. These dyscrasias may be divided into five types.