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Buchanan Ingersoll 1.\\ Rooney PC 1700 K Street, N.W., Suite 300 Washington, DC 20006-3807 Edward John Allera T 202 452 7900 202 452 7985 F 202 452 7989 [email protected] www.bipc.com Barbara A. Binzak Blumenfeld 202 452 7906 [email protected] -V1 December 1, 2015 VIA HAND DELIVERY RETURN RECEIPT REQUESTED - Division of Dockets Management U.S. Food and Drug Administration Department of Health and Human Services 5630 Fishers Lane, Rm. 1061 Rockville, MD 20852 CITIZEN PETITION On behalf of Concordia Pharmaceuticals ("Concordia" or "the Company"), sponsor of the 1 Lanoxin ® (digoxin tablets) new drug application ("NDA"), the undersigned submit this Citizen Petition ("Petition") and accompanying Expert Statement2 in five parts (one original plus four copies) pursuant to § 505Gi of the Federal Food, Drug, and Cosmetic Act ("FFDCA" or "the Act") and 21 C.P.R. § 10.20, § 10.30, and Part 320. Concordia requests that the Acting Commissioner of Food and Drugs take two specific actions. First, the U.S. Food and Drug Administration ("FDA" or "the Agency") should amend the May 2008 digoxin tablets bioequivalence guidance to reflect digoxin's narrow therapeutic index ("NTI") drug status and recommend more appropriate bioequivalence tests and specifications. Second, FDA should change the therapeutic equivalence rating for the approved generic digoxin tablet products in the "Approved Drug Products with Therapeutic Equivalence Evaluations" ("Orange Book") from AB to BX because they do not meet appropriate bioequivalence and other requirements to be considered therapeutically equivalent and therefore substitutable. FDA has long recognized that digoxin is an NTI drug product due to the narrow window between efficacious and toxic doses, as well as the need for therapeutic monitoring and dose adjustments. Digoxin was first marketed before 1938 and, in the 1970s, existing digoxin products were subject to FDA's batch certification program to ensure appropriate dissolution, potency, and bioavailability. Lanoxin was the first historical digoxin tablet product to receive NDA approval in 1997, and it is the reference listed drug ("RLD"). 1 NDA 20-405 (approved September 30, 1997). 2 Expert Statement ofManju Beier. 3 Codified at 21 U.S. C. § 355G). Division of Dockets Management U.S. Food and Drug Administration Department of Health and Human Services December 1, 20 15 Page2 The Agency's views on NTI drug bioequivalence have evolved in recent years in conjunction with the recommendations of the Advisory Committee for Pharmaceutical Science and Clinical Pharmacology ("AC"). These recommendations impact the design and acceptable pharmacokinetic ("PK") parameters for NTI drug bioequivalence studies. FDA agreed with these recommendations, and stated that its product-specific bioequivalence guidance documents for NTI drugs would incorporate appropriate study design and testing parameters. A number of these product-specific guidance documents, including warfarin, incorporate some of the AC's recommendations. However, the digoxin guidance was never updated to include them. FDA should therefore amend the May 2008 digoxin guidance to reflect, at a minimum, the same bioequivalence criteria that the Agency has already recommended for other NTI drugs, including: (1) 4-way, fully-replicated crossover in vivo fasting and fed studies; and (2) a reference-scaled average bioequivalence ("RSABE") approach. Concordia also urges FDA to include the AC's other NTI drug bioequivalence recommendations in the digoxin guidance as well- specifically: (3) a 90% confidence interval ("CI") for area under the curve ("AUC'') and maximum concentration ("Cmax") of 90-111.11%; and (4) a drug substance potency range of 95.0-105.0%. These requirements are imposed on NTI drugs such as oncology drugs. Four of the five abbreviated new drug applications ("ANDAs") for digoxin tablets were approved prior to issuance of the existing May 2008 digoxin guidance, and all five were approved before the AC's NTI drug bioequivalence recommendations from 2010 and 2011. Pursuant to the Agency's contemporary NTI standards, at least some of these drugs would not be bioequivalent to Lanoxin. Furthermore, ongoing concerns about digoxin bioavailability, content uniformity, dissolution, and potency- as well as recalls due to poor current good manufacturing practices ("cGMPs") and splitting digoxin tablets that may not be bioequivalent to Lanoxin - also raise bioequivalence questions. As a result, these generic digoxin products cannot be therapeutically equivalent to Lanoxin. Their AB ratings should be changed to BX. Substituting a generic drug that is not therapeutically equivalent to Lanoxin may result in sub- or supra-therapeutic doses causing severe adverse events or worse. As the RLD NDA holder, Concordia is responsible for maintaining its labeling, and inappropriate drug substitution raises significant questions of product liability for the Company. Because the safety and effectiveness of digoxin is called into question by inappropriate bioequivalence standards, specification concerns, and inadequate cGMPs, FDA should adopt the AC's recommendations for NTI drug bioequivalence studies before any generic is considered therapeutically equivalent to Lanoxin. A. Action Requested As addressed further herein, Concordia respectfully requests that FDA take the following actions: Division of Dockets Management U.S. Food and Drug Administration Department of Health and Human Services December 1, 2015 Page 3 1. Amend the May 2008 digoxin tablets bioequivalence guidance to reflect digoxin's NTI status and to recommend that generic drug sponsors meet the bioequivalence criteria recommended in other NTI drug guidance documents, including: a. Conducting a 4-way, fully-replicated crossover design for both in vivo fasting and fed studies; and b. Using an RSABE approach. Amend the digoxin guidance to reflect the AC's additional NTI drug bioequivalence recommendations, including: c. Meeting a bioequivalence range of 90-111.11% for the 90% CI for both AUC and Cmax, and require that the data "cross the one" (i.e., cross the 100% point); and d. Meeting a drug substance potency range of95.0-105.0%. 2. Determine that approved generic digoxin oral drug products are not therapeutically equivalent to Lanoxin and should therefore be rated BX. The bases for our requests are discussed in detail below. B. Statement of Grounds I. INTEREST OF CONCORDIA A. Concordia is the Lanoxin NDA Holder and Therefore Responsible for Maintaining Product Labeling Concordia acquired NDA 20-405 for Lanoxin oral tablets from Covis Pharma Sarl ("Covis") on April 21, 2015. As the current NDA holder, Concordia remains responsible for monitoring, collecting, and reporting adverse events associated with the drug product to FDA. The Company also remains responsible for updating its labeling based upon new safety and pharmacovigilance signals, which generic digoxin drug sponsors rely upon for their own product labeling. Concordia has a vested interest in ensuring that any generic digoxin drugs are, in fact, bioequivalent and therefore therapeutically equivalent to Lanoxin. Approving a generic digoxin product that does not meet appropriate NTI drug bioequivalence criteria will introduce drug variability making therapeutic substitution potentially dangerous for patients. It also creates marketplace liability risks for Concordia. These labeling responsibilities and potential liability issues are discussed in greater detail in Section V.G. herein. Division of Dockets Management U.S. Food and Drug Administration Department of Health and Human Services December 1, 2015 Page4 B. The Current Petition is an Extension of Two Earlier Petitions This current Petition is an extension of the issues raised in two prior petitions that Co vis filed in 2013. The first petition,4 filed on October 21, 2013, requested that FDA require all ANDA sponsors of digoxin 0.0625 mg and 0.1875 mg dosage strengths to conduct and pass all validation testing that FDA required Covis to perform, namely dissolution and blend uniformity. That Bioequivalence Petition also requested that FDA not grant testing waivers for these two dosage strengths. Covis filed a second petition5 on October 21, 2013 asking FDA to confirm that the Agency had not fully approved the 0.0625 mg and 0.1875 mg Lanoxin tablets in 1997, and that the awarded three-year exclusivity for these two strengths only began running in October 2013 when FDA approved Covis' prior approval supplement ("PAS") containing the validation testing refe1Ted to above. FDA has not yet responded to this Exclusivity Petition or to the Bioequivalence Petition. Neither petition requested amendment of the digoxin bioequivalence guidance to reflect digoxin's NTI status, and neither raised the issue of therapeutic equivalence. As a result, this current Petition is intended to complement and not duplicate those previous 2013 submissions. Because the issues are inteiTelated, Concordia requests that FDA render decisions on all of the petitions at the same time. II. DIGOXIN BACKGROUND A. Digoxin is an NTI Drug Digoxin is a cardiac glycoside used to treat a number of cardiovascular conditions. Lanoxin tablets are indicated for (1) treatment of mild to moderate heart failure in adults; (2) increasing myocardial contractility in pediatric patients with heart failure; and (3) control of resting ventricular rate in patients with chronic atrial fibrillation in adults. 6 Digoxin is an NTI drug because therapeutic levels are only slightly lower than toxic