Supplementary and sensitivity analyses
To assess the potential impact from other drugs interacting with warfarin, the main analysis was repeated excluding patients filling of a prescription for other potentially interacting drug in the observation period (8 weeks before to 12 weeks after the date of statin initiation). These drugs included specific antifungals, macrolides, quinolones, metronidazole and amiodarone as described in Appendix B.10
Furthermore, the main analysis was repeated excluding patients with a mechanical heart valve, identified through the NPR 21to assess the potential influence of this patient group with other target INR ranges than 2-3.22
Finally, some INR measurements were labeled as imprecise (up to 5-7% higher than actual values) due to prolonged storage of the blood sample before analysis of INR. We therefore conducted an analysis were these INR measurements were discarded.