Drug Interaction Study of Lopinavir/Ritonavir and Gemfibrozil (GEM-PK)

Hyperlipidemia continues to be a common problem in individuals with HIV, particularly those receiving HIV protease inhibitors (PIs) or the nucleoside reverse transcriptase inhibitor, stavudine. PI-treated patients have been noted to have increases in low-density lipoprotein (LDL), triglycerides (TG), and total cholesterol compared to PI-treatment naive individuals. The prevalence of lipid abnormalities in patients receiving PI-containing therapy has been estimated at 27-57 percent; moreover, cardiovascular complications have begun to be revealed. Triglyceride elevations, in particular, are not only an independent risk factor for the development of coronary artery disease, but may also lead to pancreatitis. Despite treatment with fibric acid derivatives, such as gemfibrozil, TGs typically remain elevated above the upper limit of normal in HIV-infected subjects. One possible reason for persistently elevated TGs in these patients is reduced efficacy of their fibric acid therapy, which may result from an unrecognized drug-drug interaction. Fibric acid derivatives are metabolized in the liver via uridine 5'-diphosphate-glucuronosyl transferase enzymes (UGT), which are induced by the HIV PI ritonavir. Indeed, ritonavir significantly lowers plasma concentrations of other drugs metabolized by this enzymatic system by 40-50 percent. As UGT activity is induced, the metabolism of UGT substrates (gemfibrozil) will increase, resulting in a decrease in their plasma concentrations. Preliminary data in non-HIV-infected subjects suggest that reduced plasma concentrations of gemfibrozil are likely to result in reduced efficacy of the drug. Despite the fact that many HIV-infected patients with hypertriglyceridemia are likely to be receiving triglyceride-lowering therapy with a fibric acid derivative while simultaneously receiving antiretroviral therapy that includes ritonavir (i.e. lopinavir + ritonavir [LPV/r]), these two drugs have not been studied in combination to determine whether or not they interact. The objective of this study is to characterize the impact of LPV/r on the pharmacokinetic (PK) profile of gemfibrozil, after a single 600 mg oral dose, administered to healthy volunteers. In a longitudinal study design, fifteen subjects will receive a single, 600 mg dose of gemfibrozil before and after 13 days of LPV/r 400/100 mg twice daily. Gemfibrozil pharmacokinetics will be determined on days one and 14 and compared using the student t-test. Results from this study will provide (or refute) the rationale for further studies designed to assess the possibility of dose-adjusting gemfibrozil when it is given in combination with ritonavir in order to maximize the pharmacologic effects of gemfibrozil.