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Executive Summary

THE CHLORZOXAZONE/ASPIRIN ANDA SUITABILITY DEPENDS ON CLINICAL TRIALS demonstrating the drug's safety and efficacy, FDA Office of Drug Standards Director Peter Rheinstein, MD, stated in a Sept. 3 letter to McNeil. "The agency has determined that investigations consisting of adequate and well controlled clinical trials are necessary to show the safety and effectiveness of the proposed product. Thus, the product is not suitable for submission as an ANDA," Rheinstein stated. McNeil petitioned FDA for a determination that chlorzoxazone and aspirin 250/325 mg tablets are ANDA suitable. The firm had claimed that the chlorzoxazone/aspirin combo is pharmacologically related to a DESI-effective drug, i.e. methocarbamol/ aspirin, and that chlorzoxazone is a listed ingredient that may be substituted for another ingredient in a listed combo drug under the FD&C Act. Rheinstein explained that the agency's aspirin/acetaminophen substitution policy is limited to those ingredients. "It appears that you may have misinterpreted the agency policy of allowing substitution between aspirin and acetaminophen in combination, to mean an acceptance of substitution among different chemicals with similar pharmacological activity which are found in combination with aspirin or acetaminophen," Rheinstein said. He noted that McNeil's petition implied a similarity between the proposed and the currently approved meprobamate/aspirin combos. While acknowledging that FDA has allowed substitution between acetaminophen and aspirin in combos based on "extensive scientific knowledge and long term experience," Rheinstein explained that "no comparable experience and scientific knowledge exists with regard to substitution between chlorzoxazone and meprobamate."

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