Reporting rates of adverse reactions to specialty care medicines exhibit a direct positive correlation with patient exposure: A lack of evidence for the Weber effect

Aims: The classical Weber effect describes an increase in adverse reaction (AR) reports after medicinal product authorisation, with a peak in AR reporting at the end of the second year followed by a decline, despite increasing patient exposure. The present study aimed to evaluate the validity of the Weber effect in the context of authorised medicines in a specialty care setting.

Methods: Using 6-monthly sales data as a proxy for exposure, the exposure-adjusted reporting rates for AR reports for 10 selected specialty care medicines were plotted against time. These data were also evaluated based on the source of report (solicited or unsolicited) and the nature of the AR contained within the reports (listed or unlisted). Unsolicited reports were analysed against sales volumes. Goodness of fit (R² ) was calculated and the trend representing the highest R² was selected.

Results: Study data comprised a total of 1 222 852 AR reports for 10 specialty care medicines. Amongst all of the products evaluated, none of the associated data represented reporting patterns entirely consistent with the classical Weber effect (see Figure 1). The results, however, showed a systemic direct correlation between AR reporting and sales volumes, especially throughout the first 5 years post-authorisation.

Conclusion: The study not only presents evidence of the absence of the Weber effect with specialty care medicines but also provides a substantial evidence of linear AR reporting correlating with sales volumes, especially during the first 5 years after marketing.