ANTITHROMBIN III RECOMMENDED FOR APPROVAL FOR THREE INDICATIONS

ANTITHROMBIN III RECOMMENDED FOR APPROVAL FOR THREE INDICATIONS by FDA's Blood Products Advisory Committee at its Sept. 14 meeting. Based on clinical data presented by KabiVitrum, Baxter, Cutter Biologicals, and Hoescht-Roussel, the committee recommended approval of antithrombin III (AT-III) for treatment of patients with congenital deficiency of AT-III, for patients with low AT-III levels associated with acute fatty liver of pregnancy, and as a prophylactic treatment against deep-vein thrombosis associated with hip and knee replacement surgery. All four companies have PLAs pending for AT-III products. The committee did not distinguish among company products when discussing approval of each indication. Kabi, Cutter, and Baxter all presented data on treatment of the congenital deficiency of AT-III; Baxter added the study on fatty liver of pregnancy; and Hoechst focused exclusively on the application in hip and knee surgery. All four companies have received orphan designations for their AT-III products as therapies for the congenital deficiency. Cutter and Baxter produce their products under a process licensed from Kabi. Meanwhile, Hoechst, which was originally also pursuing the deficiency indication, has now dropped it in favor of the hip and knee surgery application. FDA noted that "with respect to congenital deficiency of AT-III, no controlled trials have been performed." The supporting data for congenital deficiency applications, FDA told the advisory committee, "consist entirely of separate treatment episodes, either prophylactic or therapeutic. However, a very good argument can be made that a controlled trial in congenital deficiency would be difficult if not impossible to perform. There are several reasons for this. First, there are too few patients with congenital AT-III deficiency. Second, to do such a trial prospectively would take a very long time and would be very expensive. And, third, some feel that it would not be ethical to deny treatment to patients who are clearly at risk of thrombosis." KabiVitrum presented data on the greatest number of patients (50) for the congenital deficiency indication; Baxter reported on 15 patients and Cutter on 19. Each of the studies reported no recurrence of thrombus in patients given AT-III to prevent thrombolytic attacks during surgery for other causes, and successful resolution of all but two cases when AT-III was given as therapy after a thrombolytic event. The committee voted unanimously to approve AT-III as a treatment for the congenital deficiency condition. Committee members did point out some difficulties in the data, notably that most patients studied also received heparin in addition to AT-III, making it more difficult to distinguish the therapeutic contribution of AT-III alone. Hoechst's study of AT-III's effectiveness in preventing thrombosis in patients undergoing hip and knee surgery had a much larger patient population. The committee voted for approval five to one, with one abstention. Because these surgeries require an arterial tourniquet, patients are particularly prone to venous thrombosis. Hoechst said that there is as great as a 70% incidence of thrombolytic events after the operation. Hoechst delivered data on 103 patients who had undergone total hip replacement and 73 who had had total knee replacements; both groups were randomized to receive either AT-III or dextran as a prophylaxis. In the hip replacement group, the AT-III patients had a post-op thrombosis incidence of 7%, compared to a 40% incidence among patients getting dextran. The knee replacement group saw a 35% incidence of thrombosis among AT-III patients; among those receiving dextran, the incidence was 80%. The third condition for which AT-III use was approved, fatty liver of pregnancy, was described by Baxter as an extremely rare, life-threatening disease of the liver occurring in pregnant women in the third trimester. Very low or non-existent levels of circulating AT-III are a feature of the condition. Baxter presented data on nine women who were successfully restored to normal AT-III levels through AT-III therapy. The committee recommended approval again with a five to one vote.