SILVER SPRING, Md.Advisory Committee raised no significant objections on Thursday toWinRho SD, Univax Biologics Inc.'s polyclonal antibody preparationto treat acute and chronic idiopathic thrombocytopenic purpura (ITP).The product appears to be on track for approval, and FDA officials saidthat no further public review of the drug will be necessary."We'll take it internally from here," Curtis Scribner, deputy director ofthe Division of Blood Applications in FDA's Office of Blood Researchand Review (OBRR), told BioWorld. "But there's plenty more to do."A shortened discussion of the WinRho product license application(PLA) was sufficient for FDA purposes because the agency has nosignificant safety concerns about the drug, according to Scribner.Usual procedure for full review of a new drug often includes a day-long discussion of PLA data, ending in a formal vote by an advisorycommittee.Scribner declined to estimate a date for formal FDA approval of theproduct. Univax filed its PLA for approval to market WinRho SD inthe U.S. last June, a mere nine months ago. In his introduction toThursday's discussion, OBRR's deputy director of the Division ofHematology, Donald Tankersley, noted that due to user fee regulations,"we need to move quickly."The WinRho SD PLA was based on five Phase III clinical studies inadults and children with acute and chronic ITP, as well as in patientswith AIDS-related ITP. The primary indications include treatment ofITP, treatment of ITP secondary to HIV and prevention of Rhisoimmunization in newborns. The product was approved in Canada in1980 for the prevention of Rh isoimmunization, but has not yet beenapproved there as a treatment for ITP.ITP is a severe blood disorder that afflicts children and adults,including approximately 11 percent of people infected with HIV. Thedisorder is characterized by abnormally low platelet levels and risks ofexcessive bleeding and bruising. The WinRho SD preparation isproduced by stimulating plasma donors with Rh-positive blood cells.The SD signifies solvent-detergent, a method used to insure viralinactivation of the blood-derived product.One primary endpoint of the WinRho trials was an increase in plateletcounts above baseline levels. According to the company's presentation,WinRho achieved a significant increase in platelet counts in all fivestudies and was generally well-tolerated by patients. The only serioussafety concern raised by committee members and the FDA was theoccurrence of anemia potentially caused by a deficiency ofhemoglobin. However, Scribner concluded that careful monitoring ofhemoglobin levels by prescribing physicians might adequately addressthe problem.
Scott Harkonen, vice president of medical and regulatory affairs atUnivax of Rockville, Md., said that anemia was a manageable andanticipated side effect of WinRho therapy. He added that the companyis studying the compound's effect on hemoglobin levels in a trial inhealthy patients, which will be complete in four to five weeks. TheFDA did not request the study nor will the agency likely delay itsdecision on WinRho to wait for the results, Harkonen told BioWorld.Committee members queried company officials about the study designof several of the five trials in the PLA, including problems with patientenrollment and statistical methodology. When Scribner presented FDAconclusions about the product, he noted that several of the trials were"suboptimal" in design. But the agency concluded nonetheless that allof the studies were "very supportive" of WinRho's efficacy for acute,chronic and HIV-related ITP.Current standard therapies for the treatment of ITP include intravenousimmune globulin (IVIG), chemotherapy, steroids and splenectomy.Advantages of WinRho therapy over existing therapies include asmaller volume of drug needed per patient, a shorter infusion time,potentially fewer side effects and a smaller protein load. In addition,the company suggested Thursday that WinRho would be priced lowerthan IVIG.Univax licensed the U.S. marketing rights for WinRho SD inNovember of 1992 from the Canadian company Rh Pharmaceuticals.In November 1993, Univax received orphan drug designation for theproduct from the FDA.
-- Lisa Piercey Washington Editor
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