Abstract
Poor oral bioavailability is the single most important challenge in drug delivery. Prominent among the factors responsible for this is metabolic activity of the intestinal and hepatic cytochrome P450 (CYP450) enzymes. In preliminary studies, it was demonstrated that 8-arm-PEG was able to inhibit the felodipine metabolism. Therefore, this report investigated the oral bioavailability-enhancing property of 8-arm-PEG employing detailed in vitro, in vivo, and in silico evaluations. The in vitro metabolism of felodipine by cytochrome P450 3A4-expressed human liver microsomes (HLM) was optimized yielding a typical Michaelis-Menten plot through the application of Enzyme Kinetic Module software from where the enzyme kinetic parameters were determined. In vitro investigation of 8-arm-poly(ethylene glycol) against CYP3A4-catalyzed felodipine metabolism employing human liver microsomes compared closely with naringenin, a typical grapefruit flavonoid, yielding IC50 values of 7.22 and 121.97 mu M, respectively. The investigated potential of 8-arm-poly(ethylene glycol) in oral drug delivery yielded satisfactory in vitro drug release results. The in vivo studies of the effects of 8-arm-poly(ethylene glycol) on the oral bioavailability of felodipine as performed in the Large White pig model showed a > 100% increase in plasma felodipine levels compared to controls, with no apparent effect on systemic felodipine clearance. The outcome of this research presents a novel CYP3A4 inhibitor, 8-arm-poly(ethylene glycol) for oral bioavailability enhancement.