The Food and Drug Administration approved on Friday a combination drug developed by Merck that lowers a patient’s cholesterol but has not been shown to reduce the risk of cardiovascular disease or death, the company said. The drug pairs Merck’s Zetia, which lowers low-density lipoprotein (LDL or “bad cholesterol”) with the generic version of Lipitor, the best-selling statin made by Pfizer that lost its patent protection in 2011. Although the combination drug, to be called Liptruzet, was shown in a clinical trial to reduce LDL cholesterol more than patients who took Lipitor alone, the company said Liptruzet did not reduce patients’ chances of developing heart disease. That fact troubled some cardiologists, who questioned why it was approved. “This is extremely surprising and disturbing,” said Dr. Steven E. Nissen, chairman of the department of cardiovascular medicine at the Cleveland Clinic. Cardiologists have long questioned the value of Zetia and Vytorin, which combined Zetia wit