(Reuters) - U.S. health regulators approved a nonprescription version of Merck & Co Inc's Oxytrol to treat overactive bladder in women ages 18 and older, the agency said on Friday. The U.S. Food and Drug Administration said the over-the-counter version of Oxytrol would be available for women only and that the drug remained available to men by prescription only. Oxytrol for Women is a patch that contains oxybutynin, a medicine that helps relax the bladder muscle, and is designed to be applied to the skin every four days, the FDA said. ...