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Executive Summary

J&J's OMADINE MDS DANDRUFF SHAMPOO IS "MOLECULARLY DISTINCT" from pyithione zinc, Procter & Gamble maintained in June 19 comments to FDA.. P&G objected to J&J's petition requesting that omadine MDS be declared ANDA suitable on the basis of its comparability to pyrithione zinc, the active ingredient in P&G's Head & Shoulders shampoo. "The two materials have different physical and chemical properties which in and of themselves are sufficient reasons to conclude that data for pyrithione zinc cannot be used to judge either the safety or effectiveness of omadine MDS," P&G stated. P&G argued that "pyrithione zinc is a particulate solid, virtually insoluble in a shampoo matrix, while omadine MDS is a soluble material." The firm noted that FDA's OTC advisory panel concluded "the effectiveness of a pyrithione zinc shampoo formulation is dependent upon the deposition of fine particles on the scalp which resist rinsing off with water." In addition, P&G maintained there are differences in safety profiles between the two ingredients. "A key toxicity issue associated with any pyrithione derivative is central peripheral distal axonopathy," P&G said. "Of particular note, the dose for producing neurotoxicity for a soluble pyrithione, such as NaPT, is much lower than [for] an insoluble pyrithione, such as pyrithione zinc." The firm said that in order to establish the safety of omadine MDS, the no-effect dose for toxicity and the human exposure to the ingredient under use conditions must be determined. P&G asserted that FDA should not allow the marketing of omadine MDS "(1) without direct demonstration of antidandruff efficacy through at least two well controlled human clinical studies under normal use conditions, and (2) without specific demonstration of the safety of omadine MDS through a combination of animal studies and human clinicals designed to assure the existence of an adequate safety margin between no effect doses in animals and systemic loads in humans." At a minimum, P&G stated, FDA should require that bioavailability and bioequivalence testing be performed under conditions of normal shampoo use. With respect to the efficacy of omadine MDS, P&G maintained that "there is no compelling evidence that omadine MDS has inherent antidandruff activity." The firm asserted that "the single small base size foreign clinical study" cited by J&J to support the efficacy of the ingredient "is so seriously flawed that the validity of the data and their analysis as well as the blindness of its execution are highly questionable." For example, P&G said, at least 282 subjects entered the study, but data on only 77 subjects is reported.

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