Inherent limitations of the yellow card system for the detection of unsuspected adverse drug reactions.

The number of cases of an adverse reaction which could be seen by individual doctors was investigated taking realistic values for the frequency of drug prescribing and a range of frequencies of adverse drug reactions. The results indicated that, for almost all drugs, general practitioners (GPs) will seldom see other than single cases of an adverse reaction. It is argued that doctors will be unlikely to recognize an adverse reaction from a single case (unless it presented with some striking clinical features) so that potential new adverse reactions will rarely be reported by GPs under the Yellow Card scheme. A similar analysis for hospital doctors indicated that clinicians working in some specialties, may have a greater chance of seeing more than one case of an adverse reaction. A review of the identification of several important adverse reactions revealed that all the reports from British doctors were submitted by clinicians with hospital appointments. This study suggests that the major part of the operation of the Yellow Card system will contribute little to the identification of adverse reactions and that its organization and activities need to be reassessed. A modified system designed to encourage reporting by hospital clinicians could be of greater value.