2.2 Safety outcomes
The primary outcome in the illustrative analysis was the occurrence of any haemorrhagic or thromboembolic event following OAC exposure. These events could occur at any point during the observation period, as long as the criteria for drug exposure was fulfilled (as mentioned above under ‘2.1 Sample cohort assembly and drug exposure ’). The list of events considered (along with their OMOP concept IDs) are listed in the Supplementary Material. Two separate queries were written to identify haemorrhagic and thromboembolic outcomes, respectively. Each query returned the sequence of OAC exposure followed by the occurrence of the event(s), if any. Only events that occurred following OAC exposure were extracted. If a patient had both haemorrhagic and thromboembolic events, the earlier outcome was considered.
Patients in the cohort were then grouped according to their OAC drug exposure. Patients in each group were analysed for the type of diagnosis as well as for the use of any concurrent medications that may potentially exacerbate bleed risks, for example anti-platelets like aspirin or clopidogrel, for seven days prior to any haemorrhagic event. Specifically, these concurrent medications were only included if the concurrent period of exposure fell within the preceding seven-day period of the event. For instance, if a patient was dispensed with aspirin for a period of three months on 1st January 2013 and the haemorrhagic event occurred on 1st March 2013, this was considered as concurrent exposure since the dispensing period (and theoretical exposure period) includes the bleeding event date. Conversely, if another patient was dispensed with aspirin for a period of two weeks on 1st January 2013, and the event occurred on 1st February 2013, this would be excluded as concurrent exposure.