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Keryx CEO vs. a Short-Seller: Zerenex Patent Debate

Stocks in this article: KERX AMRN

Bentsur: An interesting data point for people to think about is Ferrlecit, an IV iron ferric gluconate compound that was able to obtain NCE, when there were two ferric dextran IG iron formulations that were approved prior to Ferrlecit's approval. Why would the FDA grant Ferrlecit an NCE, if the active moiety is ferric just like the prior ferric IV iron drugs. The answer we believe is that the sponsor was able to prove to the FDA from an inorganic chemistry perspective that Ferrlecit's physiochemical properties, mainly its high molecular weight complex structure, were critical for its improved activity as an IV iron formulation compared to the other IV iron compounds. We don't believe it will be difficult to prove that Zerenex represents a different complex compared to any OTC ferric citrate or any other ferric-based compounds.

Keryx short-seller: Ferrlecit's approval and NCE status designation occurred before the FDA convened an in-house working group in 2000 to address issues about the granting of market exclusivity for metal-based drugs with equivalent active ingredients. The result of this FDA working group was a more restrictive policy on the granting of NCE status. For example, Venofer, another IV iron, came up for review after the FDA's implemented changes recommended by the metals working group. FDA approved Venofer but did not grant NCE market exclusivity. FDA concluded that Venofer's active ingredient, ferric iron, had already been approved in several other drugs. Bentsur is not telling the complete story when he mentions Ferrlecit's NCE designation but omits Venofer NCE rejection. The latter is far more relevant to Zerenex.

Bentsur: With that perspective in mind, let me also discuss ferric ammonium citrate that has been mentioned as a potential impediment for Zerenex obtaining patent term extension. Ferric ammonium citrate is altogether a different salt and complex molecule with a different USB classification. Clearly, these are also different complexes and that would be very easy to prove in vitro if necessary, but the difference is so clear even organically, ferric ammonium citrate has two ph ket irons and one n iron compared to Zerenex which has one ket iron and one n iron. Secondly, it's activity as a phosphate binder has never been clinically proven and arguably it would have a very different activity profile. For example, it is likely to cause complications such as metabolic acidosis due to the ammonium component. Third, for the ferric ammonium citrate USB monographs. One of the impurity test for making ferric ammonium citrate is the absence of ferric citrate, meaning you cannot have ferric citrate in the ferric ammonium citrate salt. It is considered an impurity when making ferric ammonium citrate. Also, the fairly recent PhotoCure precedent whereby a methyl ester of an approved salt received patent from extension is reassuring. In particular, given the fact that we don't believe that ferric ammonium citrate and ferric citrate are the same salt or salt of one another and even if they were derivatives of one another, the PhotoCure precedent is very favorable. Bottom line, we strongly believe that ferric ammonium citrate will not be an impediment to patent from extension.

Keryx short-seller: I don't think the approval ferric ammonium citrate is relevant to the NCE argument. There is more than enough precedent established by the metal complex working group to eliminate NCE from consideration. The Photocure decision is relevant because it was subsequently appealed and the Federal Circuit court ruled that "product" equals the "active moiety." In fact, current FDA guidance now specifically states that altering an active moiety by changing its ester or salt does not constitute a new active moiety.

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