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New Paroxetine Salt Approved for Use

Cheryl A. Thompson

The Food and Drug Administration (FDA) has approved the marketing of paroxetine mesylate for the treatment of depression, obsessive-compulsive disorder, and panic disorder, Synthon Pharmaceuticals Ltd. announced Monday. 

Paroxetine hydrochloride, another salt of the selective serotonin-reuptake inhibitor, was approved by FDA in 1992. In FDA terminology, the two salts of paroxetine are pharmaceutical alternatives, not pharmaceutical equivalents, and thus a comparison of those products is not eligible for designation with an "A" or "B" code in the agency's Approved Drug Products with Therapeutic Equivalence Evaluations, or Orange Book

According to a Synthon spokesman, approval of the paroxetine mesylate product was achieved through a process in which the company established bioequivalency between its product and Paxil, GlaxoSmithKline's paroxetine hydrochloride product, but referred to information that FDA already had on file regarding the safety and efficacy of paroxetine, "the active moiety." 

Final labeling, including the brand name of the new product, has not been approved by FDA, the spokesman said. The Netherlands-headquartered company, he said, is negotiating with a distributor for the U.S. market and hopes that the product will be available in the fourth quarter of 2003 or sooner. 

Gary Yingling, a pharmacist and Synthon's legal counsel, said the contraindications to use of paroxetine mesylate are the same as for paroxetine hydrochloride. "The mesylate or the hydrochloride is broken off in the gut," he said, leaving paroxetine as the molecule responsible for the product's effects in patients. 

As for the language on prescriptions, Yingling said pharmacists could fill orders for "paroxetine" with either drug salt but, in most areas of the country, could not automatically substitute paroxetine mesylate in orders for "Paxil."