[Ambulatory heparin-antivitamin K relay]

In order to reach the active threshold as quickly as possible, heparin is usually given at the onset of anticoagulant therapy. The risk of thrombopenia is reduced by early initiation of antivitamin K drugs which also simplifies the treatment regimen and reduces costs. During this transition period, the desired level of hypocoagulation is attain by two mechanisms. Treatment effectiveness, side effects and interactions must be monitored regularly with the active participation of the patient after discharge. Laboratory tests for monitoring heparin therapy, including activated cephalin time for non-fractionated heparin and anti-Xa activity for low molecular weight heparin and biweekly platelet counts are maintained. Antivitamin K therapy is initiated without a loading dose and followed with coagulation time expressed in INR (isocoagulability = 1) at regular intervals, depending on the half-life of the chosen drug, for adapting dosage. Heparin can be withdrawn when the INR has reached equilibrium between 2 and 3. For ambulatory patients, the protocol must be rigorously applied and requires at least four laboratory tests over a period of six days. Except in cases of emergency, the two treatments are given simultaneously for a period of about one week which means that the antivitamin K must be given within 72 hours in order not to override the generally accepted duration of heparin therapy of ten days.