Determinants of signal selection in a spontaneous reporting system for adverse drug reactions

Detection of new adverse drug reactions (ADR) after marketing is often based on a manual review of reports sent to a Spontaneous Reporting System (SRS). Among the many potential signals that are identified, only a limited number are important enough to require further attention. The goal of this study is to gain insight into factors contributing to the selection and dissemination of possible signals originating from the SRS maintained by the Netherlands Pharmacovigilance Foundation.

In a case control design, all signals (n = 42) disseminated to the Medicines Evaluation Board from the second quarter of 1997 until the third quarter of 2000, which could be expressed as a combination of a single ATC code and a single WHO preferred term, were included. For each case, four controls were matched in time. Logistic regression analysis was used to investigate the influence of various factors, such as the fact whether the ADR or drug is new, the strength of the association, the seriousness of the reaction and the documentation of the reports.

Multivariate analysis showed that the presence of a 'serious report' (Odds Ratio 3.8, 95% CI 1.3, 11.0), a WHO 'critical term' (OR 4.7, 95% CI 1.8, 13), the ADR being unlabelled (OR 6.1, 95% CI 2.3, 16) and the presence of a disproportionate association (OR 3.5, 95% CI 1.4, 8) were all independently associated with signal selection. The number of reports and the time after marketing of the drug had no influence.

This study showed that selection of signals is based on both qualitative and quantitative aspects. Knowledge of these factors may improve the efficiency of the underlying signal selection process.