Warfarin bioavailability with feeding tubes and enteral formula

Earlier literature showed reduced efficacy of warfarin when co-administered with enteral nutrition formulas through feeding tubes. This study used an in vitro model for gastric administration of warfarin through a feeding tube to evaluate potential causes for reduced warfarin absorption when administered through feeding tubes.

There were 2 phases of the study. The first phase used an artificial stomach model with or without the infusion of enteral nutrition formula. Warfarin was added to the contents either directly into the vessel or passed through a feeding tube. Warfarin tablet dissolution was compared to the injectable formulation, which served as a control. The second phase used chopped feeding tube material added to beakers containing warfarin in increasing amounts.

Warfarin injection and tablet formulations showed decreased solubility when combined with acid. The warfarin solubility was higher when enteral formula was added. Warfarin concentration dropped by 35% when the drug was passed through a feeding tube, as opposed to added directly to the flask.In the second study, the warfarin levels were lower in the beakers containing feeding tubes. Doubling the amount of warfarin added did not raise levels to that of the initial dissolved. Doubling the amount of feeding tube material further reduced the concentration dissolved.

Feeding-tube administration compromises the total amount of warfarin reaching patients. It appears, from this in vitro study, that the mechanism of the interaction of warfarin may be a result of direct binding to the feeding tube.