Factors Influencing Concomitant Use of Complementary and Alternative Medicines with Warfarin

Aim: To investigate factors influencing complementary and alternative medicines (CAM) use among patients on warfarin. 

Method: Cross-sectional study of randomly selected patients at a hospital-based anticoagulation clinic in Malaysia. A 38- item validated data collection form was used to interview patients and investigate the reasons, perceived efficacy and adverse drug events experienced. Data were also collected on potential drug interactions and the international normalised ratio (INR). 

Results: Of the 138 randomly selected patients, 76 (55%) reported using CAM - 46 (61%) used biologically based practices such as herbal products, vitamins and supplements. Monthly household income (p = 0.05, r = 0.13) and family history of CAM use (p = 0.001, r = 0.32) were significantly associated and positively correlated with CAM use. 19 patients reported adverse events with warfarin use while none reported adverse events with CAM use. 19 and 58 patients, respectively, were identified as being at risk of potential interactions between warfarin-CAM and warfarin-conventional medicines. No significant difference in the mean INR was found between CAM and non-CAM users. 

Conclusion: A large number of patients attending the anticoagulation clinic reported using CAM. Socioeconomic factors such as monthly household income, education level and family history of CAM use were significantly related with CAM use. Routine medication interviews should include questions about concomitant CAM use.