Current practice in reporting exposure in pharmacoepidemiological studies

Background: Exposure definitions vary across pharmacoepidemiological studies. As different definitions can lead to different results, transparent reporting of the exposure definition is of utmost importance. Objectives: This study assessed the current status of reported exposure definitions in pharmacoepidemiological research as baseline measurement compared to the ISPE-ISPOR taskforce reporting guideline published in 2018. Methods: We systematically reviewed all observational pharmacoepidemiological studies that used routinely collected health data. We included studies with > = 250 subjects published in 2017 in six leading (pharmaco-)epidemiological journals. Information was extracted about all items regarding reporting of exposure as presented in the ISPE-ISPOR guideline. Primary outcome was the percentage of studies reporting each ISPE-ISPOR guideline item. Results: 91 studies were included. Almost all studies reported the type of exposure (e.g. current use, cumulative dose) (n = 89, 97.8%), the exposure risk window in general terms (n = 77, 84.6%) and the exposure assessment window (n = 89, 97.8%). The operationalisation of the exposure window was poorly described: only 14 (15.4%) studies explicitly reported the presence or absence of an induction period, 5 (5.5%) respectively 21 (23.1%) studies reported how they handled stockpiling and bridging of exposure episodes, and 28 (30.8%) studies mentioned how long the exposure was extended. How switching between drugs was dealt with and specific drug codes were reported in 52 (57.1%) and 24 (26.4%) publications. Conclusions: Reporting of exposure definitions in current pharmacoepidemiologic studies is suboptimal when compared to the ISPOR-ISPE guideline. Publications of pharmacoepidemiological studies should include more details on exposure ascertainment to allow both replication and quality assessment.