The DSRU monitors the literature and the worldwide web for important drug safety signals generated elsewhere, particularly those that cause public health or regulatory concerns. The Unit also receives requests from regulatory authorities and manufacturers to investigate drug safety signals in the PEM database. Whenever possible the DSRU conducts retrospective analyses (which usually include follow up of reports for the drug in question and comparator drugs). Such analyses contribute to the debates on these signals and to regulatory and public health decisions.
One example is the study on sertindole (Wilton et al., 2001). Sertindole is an atypical antipsychotic known to be associated with prolongation of the QTc interval. The product was withdrawn from markets in the European Union following reports of sudden death and serious cardiac arrhythmias. The comparative analyses of the PEM studies of sertindole and two other atypical antipsychotics, risperidone and olanzapine, studied cardiovascular events, deaths from cardiovascular events as well as deaths from other causes such as suicide. The report of the comparative analysis was considered to be a very important source of information for the regulatory decision on the matter.
Another example of a retrospective analysis of a PEM study is the analysis conducted on the association between selective serotonin re-uptake inhibitors (SSRIs) and bleeding, which showed a possible weak association (Layton et al., 2001).
While such comparisons produce valuable additions to the understanding of the safety of medicines, it is important to emphasise that comparisons of independent cohorts are subject to bias and confounding, which must be taken into consideration in the analysis and evaluation process. However, the paucity of post-marketing safety studies in large populations makes the information provided by these comparative studies very useful. Real benefit can only be achieved when not only the limitations of any post-marketing safety study are taken into consideration but when its results are considered in relation to other studies that had been conducted on the same product.
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