Effect of Body Weight on Dose of Vitamin K Antagonists

Timothy H. Self, PharmD; Jessica L. Wallace, PharmD, BCPS; Sami Sakaan, PharmD, BCPS; Christopher W. Sands, MD


South Med J. 2015;108(10):637-643. 

In This Article


Although most evidence suggests that body weight affects VKA dosing, further study is needed. The available literature more strongly suggests a correlation between VKA dose and body weight in obese and morbidly obese patients, with a decreased response to VKA warranting higher initial doses to maintain a therapeutic INR.[5,11] Given that more than one-third of the US population is obese,[36] this clinical consideration is commonly encountered in practice, and providers need to be reminded to pay attention to the patient's body weight when initiating VKA. Based on the available evidence, we suggest an initial increase in VKA dose of approximately 30% in obese patients and up to 50% in morbidly obese patients in addition to considering other established variables.[5,11] Also, clinicians should take into consideration that the time to reach a therapeutic INR can be prolonged in these patients. Further studies are needed to fully investigate this correlation to provide initial dosing guidance for obese and morbidly obese individuals.