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.