With the Food and Drug Administration’s approval of Pristiq, Wyeth said the company planned a big sales effort to introduce the product to psychiatrists and primary care doctors.

Dr. Philip Ninan, a Wyeth vice president for neuroscience, said he thought that Pristiq, which is chemically similar to Effexor, would have similar benefits in treating major depression. But the company said the drug had distinct advantages over its existing product.  Another advantage is that Pristiq does not have to be broken down by the liver, Dr. Ninan said, so it is not likely to interact with other medications metabolized by the liver. Wyeth is also seeking F.D.A. approval for Pristiq as a drug to reduce hot flashes in menopause. The agency has asked for more data for that use.