FDA mulls incentives for chiral compounds

WASHINGTON - An FDA proposal released last week holds out the prospect of an additional two years of market exclusivity for newly approved drug products such as Interneuron Pharmaceuticals Inc. 's Redux dexfenfluramine whose active ingredient is a single enantiomer of fenfluramine, a previously approved racemate

FDA was prompted to revisit its policies in part by IPIC's dexfenfluramine, which was approved in April 1996 as a treatment for obesity. Dexfenfluramine was the first single enantiomer of a previously approved racemate to be approved in the U.S.

Racemic compounds contain mixtures of isomers, of which one often is associated with a drug's side effects while the other isomer provides the drug's benefits without the toxicities. Enantiomers are stereoisomers, or molecules that cannot be superimposed on their chiral pair (see accompanying definition).

Biotech companies including Sepracor Inc. (SEPR, Marlborough, Mass.) and Celgene Corp. (CELG, Warren, N.J.) and pharmaceutical companies such as Merck that are developing drugs based on enantiomers could benefit significantly if FDA implements the proposal, according to representatives of the companies and consultants specializing in chiral compounds.

Under terms of 1984 amendments to the Food, Drug and Cosmetic Act, FDA currently grants five years of non-patent protection to NDAs and ANDAs for products in which no active ingredient has been previously approved. The protection is accorded by refusing to accept additional applications for products containing the novel ingredient(s) for five years. Because of the time required to review and

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