Terminology in prescription-event monitoring.

The terminology used in prescription-event monitoring for postmarketing surveillance is described. It has been developed by the Drug Safety Research Unit while processing records of 500,000 events associated with the use of new chemical entities by 460,000 patients in England since 1981. Currently, the events are arranged in 24 classes which include 108 high-level terms and 1197 low-level terms. Low-level terms are used to code individual events reported by general practitioners, usually without an opinion about any possible causal relationship with a particular drug. Some low-level terms are lumped together as one high-level term when the event rates are estimated.