Post market Research of Oral Anti-Diabetic Drugs: Metformin, Glipizide, and Pioglitazone

The aims of this study were to document the post market research of the pharmaceutical industry and the effects of labeling revisions on post market studies and outcomes of oral anti-diabetics. A literature search identified post market studies of metformin, glipizide, and pioglitazone. Labeling revisions in MedWatch® were collected as indicators of the FDA’s response to post market drug safety. Data were analyzed by comparing industry and non-industry sponsored studies for the number of pre- and post-market studies, study sponsorship, drug labeling revisions, and outcomes after the drugs became generic. The number of industry versus non-industry sponsored studies was 149 (49%) and 155 (51%) for metformin; 33 (44%) and 42 (56%) for glipizide; and 85 (80.2%) versus 21 (19.8%) for pioglitazone. The differences in favorable results between industry and non-industry sponsored studies were similar for metformin and glipizide. The number of industry-sponsored studies with favorable results did not significantly increase after metformin or glipizide became generic. Studies sponsored by the manufacturer of glipizide reported significantly more favorable outcomes in comparison to studies sponsored by industry competitors (90% favorable, 10% neutral, 0% unfavorable, P < 0.05). For pioglitazone, significantly more favorable results were reported in industry-sponsored studies (88.2%) as compared to non-industry (66.7%) (p = 0.008) sponsored studies. A significant correlation exists between the number of pioglitazone’s labeling revisions and the number of post market studies (p = 0.008). Post market research is guided by the pharmaceutical industry and by individual researchers’ interests. Pharmaceutical industry-sponsored studies support the favorable use of the patented drug and show unfavorable results of the generic equivalent. A possible correlation exists between drug labeling revisions and the number of post market studies.