Abstract
In pharmacoepidemiological analysis, one covariate that might act as a
confounder is the type of prescriber issuing a prescription. The type of
prescriber typically fulfills the criteria for confounding, as it is
associated both with the exposure (e.g., prescriber types may differ in
their choice of first-line treatment) and with the outcome (as different
types of prescribers often treat patients with different disease
severity). Additionally, the type of prescriber may correlate with other
factors such as treatment adherence, surveillance, or coding practices.
While information on the type of prescriber is often available to
researchers, it is rarely employed to control for confounding in
pharmacoepidemiological analyses. In an applied example, we conducted a
cohort study using Danish healthcare registers from 2011 to 2018 to
assess the risk of ischemic stroke associated with the use of direct
oral anticoagulants (DOACs) compared to warfarin. We found a hazard
ratio (HR) of 0.95 (95% CI: 0.90-1.01) for DOACs versus warfarin when
adjusting only for age and sex. Further adjustment for prescriber type
showed an effect of similar magnitude (HR 0.93; 95% CI: 0.87-0.98).
However, in stratified analyses, we observed higher estimates in the
group of general practitioners (HR 1.06; 95% CI: 0.94-1.2) compared to
hospital prescribers (HR 0.88; 95% CI: 0.82-0.95), indicating potential
effect modification. This highlights the potential value of prescriber
type as an important covariate in pharmacoepidemiological analyses.
Further research is needed to fully establish the importance of
prescriber type in such analyses.