We thank Glisson and colleagues for their letter and their recognition of the inherent limitations of the research of dietary supplements marketed to consumers. The purpose of my laboratory is to conduct phase 1 electrocardiographic studies of commercially marketed herbal supplements to healthy volunteers. In this way, we strive to closely simulate the actual scenario in which a patient would purchase a product “off the shelf” at his or her local drug store and potentially experience a clinical adverse drug event during the course of self-administration. To that end, Glisson and colleagues attempt to establish the hypothesis that our study is flawed because research has shown that selected dietary supplements have demonstrated interlot and intralot variability. However, Glisson and colleagues have not produced evidence showing that the specific product we tested (Enzyte) has demonstrated interlot or intralot variability. Moreover, the Food and Drug Administration, on June 22, 2007, published a final rule requiring manufacturers of dietary supplements to adhere to current good manufacturing practices. Among other things, the final rule states that manufacturers of dietary supplements must maintain proper manufacturing operations and quality control procedures and perform end process and/or in-process testing of all components included in the preparation.1 To date, there has been no evidence that Vianda, LLC, has failed to comply with this rule.
McBride BF. Dietary Supplements: Safety Issues and Quality Control—Reply. Arch Intern Med. 2011;171(5):476-477. doi:10.1001/archinternmed.2011.54