(AP)—Merck & Co. says it is ending development of an experimental Parkinson's disease drug because the drug wasn't working.

says it reviewed initial data from three late-stage clinical trials and did not find evidence preladenant was more effective than a placebo.

The company says it doesn't plan to file for marketing approval of the drug. It says the decision was not related to any safety problems.

Shares of Merck rose 62 cents to $47.33 on Thursday. The stock lost 21 cents to $47.12 in after-hours trading.

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