Hoechst Marion Roussel, Inc., and Baker Norton Pharmaceuticals, Inc.; Terfenadine; Proposal To Withdraw Approval of Two New Drug Applications and One Abbreviated New Drug Application; Opportunity for a Hearing

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The Food and Drug Administration (FDA) is proposing to withdraw approval of two new drug applications (NDA's) and one abbreviated new drug application (ANDA) for drug products containing terfenadine. NDA 18-949 (Seldane) and NDA 19-664 (Seldane-D) are held by Hoechst Marion Roussel (HMR), Inc., P.O. Box 9627, Kansas City, MO 64134-0627. ANDA 74-475 is held by Baker Norton Pharmaceuticals, Inc., 4400 Biscayne Blvd., Miami, FL 33137. On July 25, 1996, FDA approved HMR's NDA 20-625 for fexofenadine hydrochloride (Allegra). Fexofenadine is the active metabolite of terfenadine that is responsible for the desired beneficial properties of terfenadine. When patients take terfenadine, parent terfenadine is ordinarily present in their blood at very low concentrations, because the terfenadine molecule is metabolized to form fexofenadine. Fexofenadine is responsible for providing patients with essentially all the clinical benefits of taking terfenadine. If terfenadine's metabolism is inhibited, either by another drug or by intrinsic liver disease, the level of parent terfenadine can rise to levels that can cause serious side effects in people as a result of the effect of parent terfenadine on