Drug interactions update: Drugs, herbs, and oral anticoagulation

Management of warfarin drug interactions is often complicated by lack of in formation regarding interactions with new drugs and with herbal medicinals. The pharmaceutical industry has increased both the number and quality of d rug interaction studies prior to marketing new agents. Interactions may sti ll occur in patients, however, despite negative pre-marketing studies in he althy volunteers. The clinical significance and intensity of warfarin inter actions with prescription drugs (e.g., celecoxib, proton pump inhibitors, a nd selective serotonin reuptake inhibitors) can often be predicted on the b asis of known metabolic characteristics of the drugs and warfarin enantiome rs. Drug interactions with herbal medicinals are much more difficult to cha racterize and predict because of the lack of federal regulations regarding safety, efficacy, and manufacturing standards. Published case reports of in teractions between warfarin and even the most widely used herbal medicinals are limited. Practitioners are encouraged to report such interactions thro ugh the FDA MedWatch program.