Friday's FDA approval of Hoechst Marion Roussel's Allegra antihistamine marks the first approval of an improved chemical entity developed by Sepracor Inc. (SEPR). However, SEPR will have to wait until 1998 to begin seeing a revenue stream from Allegra.

SEPR's royalties will take effect when HMR's composition of matter patent on its existing Seldane antihistimine lapses in April 1999. Allegra (terfenadine carboxylate) is a metabolite version of Seldane.