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FDA DEVELOPING GUIDANCE FOR GENERIC RETIN-A (TRETINOIN) PRODUCTS

Executive Summary

FDA DEVELOPING GUIDANCE FOR GENERIC RETIN-A (TRETINOIN) PRODUCTS, FDA Division of Anti-Infective Drug Products Dermatology Group Leader C. Carnot Evans, MD, told a topical drug products workshop cosponsored by FDA and the American Association of Pharmaceutical Scientists March 26-28. Noting that "anti-acne drugs, tretinoins, will go off patent in April of 1990," Evans said: "We are preparing guidance for the types of studies...that will probably be recommended in the show of bioequivalence." The kind of study FDA is considering for proof of therapeutic equivalence, Evans explained, would be a single randomized "double-blind multicenter parallel study comparing proposed generic products and reference product, which will be [Ortho's] Retin-A, and a placebo control in the treatment of grade 2 and grade 3 acne." The study would last 12 weeks with study size determined by statistical consultation. "The primary endpoint will be lesion counts, including inflammatory and non-inflammatory, and a global evaluation performed by the investigators at baseline and at regular intervals," Evans remarked. FDA recently released draft guidances on topical antifungal and vaginal antifungal products that require similar clinical studies for the generic versions of such products ("The Pink Sheet" March 12, p. 8). The new draft guidances resulted from a reworking of documents at a November workshop between FDA and industry members on topical antifungals. Acne products were also considered at that meeting. Generic topical corticosteroids have not been required to undergo clinical trials to show bioequivalence. The only requirement has been a vasoconstrictor test called the Stoughton assay, Evans noted. However, "in the last year or two, there have been reports that have caused us to reconsider our position on the appropriateness of the test for this purpose," Evans commented. Although FDA "would prefer to be able to continue to use this assay because it has certain utility and because it is [in] keeping with the spirit of the Waxman Hatch amendment" by remaining a relatively inexpensive procedure, Evans said, "this subject will be revisited at FDA during the months to come." The FDAer emphasized that "we need simple, inexpensive methods to predict efficacy with topical drugs and to demonstrate therapeutic equivalence." Alternative bioequivalence studies for antifungals that have been suggested include animal inocculation tests, skin stripping, perfusion through cadaver or human skin, and inocculation of an organism on human skin followed by application of the test product. However, "there are just inadequate data to accept any one of these techniques as we would clinical trials and be comfortable," Evans remarked, noting that FDA is sponsoring research on percutaneous absorption of drugs in order to find new methods of demonstrating bioequivalence for topical products.
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