Preparing for the new anticoagulants.

New anticoagulant agents with differing properties, risks, and potential economic consequences are becoming available. Two subcutaneously injected synthetic pentasaccharide anticoagulants, fondaparinux and idraparinux, employ the minimal chain length required to bind to antithrombin and confer a conformational change, increasing its ability to catalyze inactivation of activated factor X (Xa). Melagatran has also been developed as an injectable drug for markets outside the United States. Recently synthesized oral anticoagulants other than VKAs have proven effective in clinical trials. These drugs do not act by enhancing antithrombin activity, but rather act directly to inhibit the active site of thrombin (melagatran and its orally absorbed derivative, ximelagatran) or factor Xa (razaxaban [DPC-906]). Several studies have been performed with ximelagatran, an oral synthesized pro-drug developed by AstraZeneca, which is rapidly metabolized into the active agent, melagatran.