Complementary and Alternative Medicines Use in Patients on Warfarin and Matched Controls: A Retrospective Cohort Study

Abstract

Aim To investigate complementary and alternative medicines (CAM) knowledge and use in patients on warfarin and matched controls, and the association between CAM use and adverse events (bleeding or clotting). Method A retrospective cohort study was undertaken in the emergency department of a Melbourne hospital. Patients in the warfarin and control groups were those taking/not taking warfarin, respectively (groups matched for age and gender). An investigator‐administered questionnaire was used to collect data on CAM knowledge and use, and bleeding/clotting events during the previous 6 months. The international normalised ratio (INR) data during the previous 6 months were obtained from medical and pathology records. Results 246 warfarin and 246 control group patients were enrolled. Approximately 50% in each group indicated that they knew of the potential for CAM–drug interactions. Only 60 (24%) patients in the warfarin group reported having been advised about CAM use. Compared to controls, a similar proportion of warfarin patients reported CAM use (29% vs 37%; p = 0.07) and significantly fewer used a CAM known to interact with warfarin (‘interacting CAM‘) (11% vs 19%; p = 0.03). In the warfarin group, CAM users and non‐users reported a similar number of events below and above their therapeutic INR range and when the INR exceeded 5. CAM users in the warfarin group tended to have more abnormal bleeding events (42% vs 30%; p = 0.06) but a similar number of clotting events (9% vs 10%; p = 0.8) than CAM non‐users. Warfarin patients who used ‘interacting CAM’ had significantly more clotting events than those who used CAM not known to interact with warfarin (18% vs 2%; p = 0.02). Conclusion CAM knowledge in people on warfarin was poor. ‘Interacting CAM' used concomitantly with warfarin may be associated with increased rates of clotting events.

New antithrombotic therapies and complementary and alternative medicine (CAM): Chartering into unknown territory

“…Moreover these therapies, particularly warfarin, also have known potential interactions with food and complementary and alternative medicines (CAMs) [16][17][18] which, as defined by the Australian Medical Association (AMA), include a wide range of products and treatments with therapeutic claims that are not presently considered to be part of conventional medicine [19]. In Australia CAM use is substantial with more than two-thirds of the Australian adult population using at least one form of CAM [20], often in conjunction with conventional medicines and with failure to report CAM use to their doctor [20,21].…”