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Executive Summary

FDA TRANSDERMAL PATCH PHARMACEUTICAL EQUIVALENCE CRITERIA will be detailed in a Federal Register notice being prepared by the agency's Office of Generic Drugs, FDA's Donald Hare announced at the inaugural meeting of the Generic Drugs Advisory Committee Dec. 14. The document offers four basic criteria for equivalence. First, there must be equal amounts of drug in the patch reservoir, Hare said, noting: "We will go up plus or minus 10%." Patches "have to have the same controlled-release mechanism or they are not going to be considered pharmaceutically equivalent." Surface area will not be considered. "We don't feel that this is important, much like if you have a 25 mg tablet, whether the tablet is a small one or large one, as long as the 25 mgs are there," Hare said. The fourth criterion is proof of bioequivalence. Hare said three firms have developed generic transdermal patches and conducted clinical trials that proved the effectiveness of their products. These firms' ANDAs have been transferred to the Division of Cardio-Renal Drugs, which is in the process of selecting a reference drug product against which all transdermal ANDAs will be compared. Two of the ANDAs have been converted to NDA submissions, Hare said, indicating that these two products could not show bioequivalence to the pioneer drug. Noting that he had to be careful in the way he phrased his statement, Hare said: "We approve ANDAs that are bioequivalent, not necessarily because they are effective. In other words, you can have a product that proves safety and effectiveness that may not be bioequivalent." Office of Generic Drugs Director Roger Williams, MD, indicated that the transdermal patch guidance is one of a number of upcoming guidelines that will come out of the Office of Generic Drugs. "First and foremost" will probably be a guidance on conjugated estrogens. Williams also said the agency will be developing bioequivalence guidelines for big-selling drugs before they go off-patent. Williams, prefacing a presentation on the history of conjugated estrogens from Ann Witt of the Office of General Counsel, predicted: "Certainly conjugated estrogens will be topic for a future advisory committee." Witt concurred with Williams that the Generic Drugs Advisory Committee would "surely become embroiled" in the issue, adding: "I wish you luck." She noted that the question of whether bioequivalence should be based on urinary excretion studies and/or rate absorption studies has stymied two previous FDA advisory committees. Williams returned to the issue of bioequivalence guidelines for blockbuster products at a Dec. 12 session of the Food and Drug Law Institute's annual meeting. A "goal that I want to sell over the next several months is to develop guidances for the products that are coming off patent. I think industry deserves them," Williams stated. "We should offer you fairly clearcut guidelines on how to do a bioequivalence study for some of these very important drug products that are going to be available to the generic industry over the next 10 years." FDA's usual practice has been to develop bioequivalence guidelines sometime after a brandname product loses patent protection. At the Generic Drugs Advisory Committee, the agency was asked what products the agency has had in mind in developing its policy on blockbuster drugs. Tom McGinnis, of the office's legal/regulatory affairs staff, said an upcoming Federal Register notice on the issue would name about nine drugs, including Eli Lilly's Ceclor and other antibiotics. Williams told the group that the types of issues "that I'll be asking the advisory committee to be focusing on" include bioequivalence testing procedures, in vitro dissolution, and "some of these test specifications that we use to evaluate a product." Williams also said that "at some point in time, I'm fairly certain that the committee's going to get involved in this issue of scale-up and what are the scientific pertinent points regarding it." More generally, Williams commented on the office's wish to obtain support from the committee in improving the science underlying product application reviews and in developing "scientific investigation" of issues affecting generics. "And the way I see that happening is there are two areas of focus: I see science at the office level in terms of review support. In other words, getting the comments and statements of the advisory committee" on review issues. Committee member Leslie Benet, University of California/San Francisco Department of Pharmacy, emphasized his concern that the committee "should address the issue of bioequivalence for the agency as a whole," not just in relation to ANDAs. "Bioequivalence is used just as often in the NDA process" and for subsequent changes in dosage formulations, he pointed out. Committee Chairman Terrence Blaschke, MD, Stanford University Medical Center, said he would like the group to meet three times per year, probably in two-day meetings due to the complexity of the issues likely to be included on its agenda. He indicated the next meeting is being scheduled for sometime in February.

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