Cainzos-Achirica M, Varas-Lorenzo C, Pottegard A, Asmar J, Plana E, Rasmussen L, Bizouard G, Forns J, Hellfritzsch M, Zint K, Perez-Gutthann S, Pladevall-Vila M. Methodological challenges when evaluating potential off-label prescribing of drugs using electronic health care databases: a case study of dabigatran etexilate in Europe. Pharmacoepidemiol Drug Saf. 2018 Jul;27(7):713-23. doi: 10.1002/pds.4416

PURPOSE: To report and discuss estimated prevalence of potential off-label use and associated methodological challenges using a case study of dabigatran.

METHODS: Observational, cross-sectional study using three databases with different types of clinical information available: Cegedim Strategic Data Longitudinal Patient Database (CSD-LPD), France (cardiologist panel, n=1,706; general practitioner panel, n=2,813; primary care data); National Health Databases, Denmark (n=28,619; hospital episodes and dispensed ambulatory medications); and Clinical Practice Research Datalink (CPRD), UK (linkable to Hospital Episode Statistics [HES], n=2,150; not linkable, n=1,285; primary care data plus hospital data for HES-linkable patients).

STUDY PERIOD: August 2011 to August 2015. Two definitions were used to estimate potential off-label use: a broad definition of on-label prescribing using codes for disease indication (e.g., atrial fibrillation [AF]), and a restrictive definition excluding patients with conditions for which dabigatran is not indicated (e.g., valvular AF).

Prevalence estimates under the broad definition ranged from 5.7% (CPRD-HES) to 34.0% (CSD-LPD) and, under the restrictive definition, from 17.4% (CPRD-HES) to 44.1% (CSD-LPD). For the majority of potential off-label users, no diagnosis potentially related to anticoagulant use was identified. Key methodological challenges were the limited availability of detailed clinical information, likely leading to overestimation of off-label use, and differences in the information available, which may explain the disparate prevalence estimates across data sources.

CONCLUSIONS: Estimates of potential off-label use should be interpreted cautiously due to limitations in available information. In this context, CPRD HES-linkable estimates are likely to be the most accurate.

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