FDA CHOLESTYRAMINE INTERIM BIOEQUIVALENCE GUIDE TO REQUIRE IN VITRO TESTS ONLY

FDA's interim guidance on the bioequivalence testing of cholestyramine will require a series of in vitro tests rather than in vivo methods, Office of Generic Drugs Director Roger Williams told the National Association of Pharmaceutical Manufacturers mid- year meeting in Washington, D.C. June 23. The OGD's "feeling is that bioequivalence for cholestyramine can be documented on the basis of in vitro methodology," the FDAer said. "So you can see we're kind of creating an exception to the way we generally work." Williams hopes to issue the interim guide "very soon, hopefully within the next month or so." He added that his "anticipation is that that exception will occur rarely; maybe cholestyramine is one of the very few drugs where it would apply. But [the office is] going to try it and see how it works." Instead of in vivo data, the guidance would require a series of bile acid binding studies that would compare the binding of the generic version to that of the innovator resin. Other bioequivalence documents in preparation at the office include: guidances on controlled-release products, which may be issued in interim form; general bioequivalence policy; and bioanalytical validation. The last is expected "fairly shortly," Williams said. OGD hopes to bring the issue of metered-dose inhaler and albuterol metered-dose inhaler bioequivalence testing before the Generic Drugs Advisory Committee in the early fall. Studies at Johns Hopkins University on MDIs have been completed and FDA had hoped to bring them before the committee in early June, but data analysis has not been completed, Williams explained. OGD will issue an interim guidance on the subject following the advisory committee meeting, he added ("The Pink Sheet" May 24, In Brief). Another future topic for the advisory committee, possibly to be addressed in the fourth quarter of 1993, is applications of in vitro dissolution testing, including use as a surrogate marker for bioequivalence.