Warfarin-Vitamin K Interactions

Assessment of Healthcare Professionals’ Knowledge About Warfarin-Vitamin K Drug-Nutrient Interactions

R. Rebecca Couris, PhD, RPh, Gary R. Tataronis, MS, Gerard E. Dallal, PhD, Jeffrey B. Blumberg, PhD, FACN, Johanna T. Dwyer, DSc

Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University (R.R.C., G.E.D., J.B.B., J.T.D.), Massachusetts College of Pharmacy and Health Sciences (R.R.C., G.R.T.), Boston, Massachusetts

Objective: Dietary vitamin K can interact with oral anticoagulant drugs and interfere with their therapeutic safety and efficacy. Therefore, knowledge about drug-nutrient interactions involving vitamin K possessed by physicians, pharmacists, dietitians and nurses practicing anticoagulant therapy was assessed.

Methods: Healthcare practitioners were surveyed using a 30-question, 98-item questionnaire on the most common and/or important food interactions with warfarin, drug interactions with warfarin and general drug-nutrient interactions involving vitamin K. The study sample included 160 randomly selected healthcare providers (40 physicians, pharmacists, dietitians and nurses) from 10 hospitals with 200 to1000 beds from six Massachusetts regions. Random selection was conducted from a pool of selected healthcare providers practicing anticoagulant therapy who counsel patients receiving warfarin.

Results: All surveys were completed within three months of the start of the study, and all participants provided usable data for statistical analysis. The mean scores (± SD) on the overall test were 72.5 ± 9.0 for pharmacists, 62.5 ± 10.6 for physicians, 56.9 ± 8.8 for dietitians and 50.2 ± 9.3 for nurses, with 100 being a perfect score. Pharmacists scored significantly higher in the area of drug interactions (75.9 ± 11.3, p<0.05). Dietitians scored higher in the area of food interactions (73.0 ± 10.3). No significant differences between physicians and pharmacists were evident on general drug-nutrient interactions. While over 87% of the healthcare professionals correctly identified some common foods containing large amounts of vitamin K, such as broccoli and spinach, fewer than 25% were able to identify others such as pea soup, coleslaw and dill pickles.

Conclusions: Although the healthcare professionals surveyed in this study appear to have demonstrated some proficiency in their respective areas of expertise, they exhibited less knowledge in others. Therefore, additional training and integration of knowledge and expertise about drug-nutrient interactions among healthcare professionals are essential to provide appropriate patient counseling and optimal therapeutic outcomes.

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