NEW YORK (AP) — Targacept Inc. said Wednesday that a depression treatment it is developing met its goals in a midstage clinical trial, sending Targacept shares soaring. Targacept stock more than doubled in value on the news, jumping to $7.81 after closing at $3.06 on Tuesday. More than 3 million shares were traded before midday, compared with an average full-day volume of 70,000 shares. Targacept said its drug candidate, called TC-5214, significantly improved symptoms of major depressive disorder for patients who did not respond to an older drug, Forest Laboratories Inc.’s Celexa. TC-5214 was better than a placebo at improving an overall depression measurement, as well as reducing depression, irritability and severity of illness, and leading to better cognition and overall improvement. The Winston-Salem, N.C., company said it is in talks with several drugmakers to find a partner to help complete development of TC-5214. It expects to begin a late-stage trial of the drug in the second quarter of 2010 after it produces the required material and holds talks with the Food and Drug Administration. The first phase of the trial started with 579 patients who took 20 milligrams of Celexa per day for four weeks, and then 40 mg per day for another four weeks. Patients who had not experienced much improvement, and did not have very low scores on a scale used to measure depression symptoms, continued taking Celexa and were also given either TC-5214 or a placebo for the next eight weeks. The two drugs were considered comparable because they are both selective serotonin reuptake inhibitors. The patients started with 2 mg of the drug per day. Investigators were allowed to increase the dose to 4 mg or 8 mg per day. The most common side effects were headache, dizziness and constipation. One patient had a seizure. Among patients who dropped out of the trial, Targacept said there was not a significant difference between the TC-5214 group and the placebo group. Full results from the study will be presented in October at a Society for Neuroscience meeting in Chicago. Targacept does not have any products currently on the market. It is developing drugs for depression, high blood pressure, and inflammation. Through a partnership with AstraZeneca PLC, it is testing drugs for cognitive disorders, including attention deficit hyperactivity disorder and Alzheimer’s disease.