Bioequivalence of generic thioridazine drug products--the FDA viewpoint

The phenothiazines are among the most widely used drugs to treat symptoms commonly associated with acute and chronic psychoses. One of the commonly prescribed compounds within this class of drugs is thioridazine, available both as a generic product as well as the innovator product, Mellaril. Each of these products is coded as bioequivalent and consequently therapeutically equivalent by the Food and Drug Administration (FDA). A recent issue of this journal contained an article that raised a number of questions concerning the bioequivalence of the generic versions of thioridazine that have been approved by the FDA. Their article was based in part on information obtained from the FDA as well as information supplied to the authors by Sandoz, Inc., the manufacturer of the original thioridazine drug product Mellaril. The FDA has reviewed its original decision of bioequivalence. Based on this reassessment, the FDA strongly rejects the assertion by the authors that several of the approved generic thioridazine products are not bioequivalent. The rationale behind the FDA decisions and the FDA's viewpoint on the bioequivalence of generic thioridazine drug products is discussed in detail.