Patent citation analysis of new chemical entities claimed as pharmaceuticals

Abstract

Patent references are of particular interest for technology analysis because they offer a measure of patent importance and a method of identifying links between patents. Citation analysis was performed on the set of all US patents issued during the years 1993 through late 1997 that cover new chemical entities (NCEs) claimed as pharmaceuticals. Merck & Co. heads the list, with 577 patents, almost 5% of the total, Hoechst Marion Roussel is second with 499 patents, about 4% of the total, and Eli Lilly is third with 337 patents, about 3% of all patents. However, Allergan, ranked 30th by its number of patents, is the top cited company, with 975 citations, almost all coming from subsequent Allergan patents. Merck is second with 779 citations. High levels of self-citation seem to predominate in NCE pharmaceuticals, perhaps reflecting the incentives to develop proprietary niches of in-depth knowledge and capability in the industry. Thus, looking at a company’s most highly cited patents may provide insight into the fields that it believes are most important. All 25 of Allergan’s highly cited patents are for NCEs having ‘retinoid like activity’ that are clearly related to Allergan’s development of retinoid medications for skin disorders. Similarly, all seven of American Home Products’ highly cited patents deal with one topic: rapamycin, an immunosuppressant. In the NCE pharmaceutical area, patent citations, and particularly self-citations, provide additional information beyond simple patent counts about the importance of particular lines of investigation to particular companies.