Merck & Co., Inc. is a research-intensive biopharmaceutical company engaged in research to deliver health solutions that advance the prevention and treatment of diseases in people and animals. Its Pharmaceutical segment includes human health pharmaceutical and vaccine products. Human health pharmaceutical products consist of therapeutic and preventive agents, generally sold by prescription, for the treatment of human disorders. Human health vaccine products consist of preventive pediatric, adolescent and adult vaccines. The Animal Health segment discovers, develops, manufactures and markets a range of veterinary pharmaceutical and vaccine products, as well as health management solutions and services, for the prevention, treatment and control of disease in all major livestock and companion animal species. It is also engaged in developed a novel class of small molecules that target cancer cells lacking expression of a key DNA repair protein called O6-methylguanine methyl transferase.