Is reporting rate a good predictor of risks associated with drugs?

Aims: Uncertainty as to relative under-reporting plagues the comparisons of spontaneous reporting rates as a tool for decision-making in pharmacovigilance. However, it is generally accepted that under-reporting should be reasonably similar for similar drugs sharing the same indication, country and period of marketing. To test this, we compared the adverse drug reaction reporting rates to the French regional pharmacovigilance centres for six pairs of identical drug marketed at the same time by different companies under different brand names (co-marketing).
Methods: All reaction reports were related to sales, to compute reporting rate; within each pair, the reporting rate ratio and its confidence interval were calculated.
Results: The rate ratios were all between 0.76 and 1.33. Two of them were significantly different from 1 (1.28; 95% C.I. [1.01; 1.60] and 1.33; 95% C.I. [1.06; 1.74]).
Conclusions: These small differences in reporting rates would not warrant regulatory action and support the usual assumption of similar reporting for similar drugs.