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ABSORPTION, DISTRIBUTION, METABOLISM, AND EXCRETION

The Impact of G on the Oral Bioavailability of Low Bioavailable Therapeutic Agents

Pharmacokinetics-Biopharmaceutics Laboratory, Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland at Baltimore, Baltimore, Maryland (N.N.S., N.D.E.); and Division of Pediatric Gastroenterology and Nutrition and Gastrointestinal Section, Center for Vaccine Development, Department of Physiology, School of Medicine, University of Maryland at Baltimore, Baltimore, Maryland (A.F., M.T.)

Low oral bioavailability continues to drive research toward identifying novel approaches to enhance drug delivery. Over the past few years, emphasis on the use of absorption enhancers has been overwhelming despite their major adverse effects. Zonula occludens toxin (Zot) was recently established as a safe and effective absorption enhancer, reversibly opening the tight junctions for hydrophilic markers and hydrophobic drugs across the small intestine and the blood brain barrier. G, the biologically active fragment of Zot, was isolated and shown to increase the in vitro transport and in vivo absorption of paracellular markers. The objective of this study was to examine the effect of G on the oral bioavailability of low bioavailable therapeutic agents. Jugular vein cannulated Sprague-Dawley rats were randomly assigned to receive the following treatments intraduodenally (ID): [³H]cyclosporin A, [³H]ritonavir, [³H]saquinavir, or [³H]acyclovir at (120 µCi/kg) alone, with protease inhibitors (PIs), or with G (720 µg/kg)/PI. Serial blood samples were collected, and plasma was analyzed for radioactivity. After ID administration with G/PI, C_max significantly (p < 0.05) increased over a range of 197 to 5700%, whereas area under the plasma concentration time curve displayed significant increases extending over a range of 123.8 to 4990.3% for the investigated drugs. G significantly increased the in vivo oral absorption of some low bioavailable drugs in the presence of PI. This study suggests that G-mediated tight junction modulation, combined with metabolic protection, may be used to enhance the low oral bioavailability of certain drugs when administered concurrently.

Address correspondence to: Dr. Natalie D. Eddington, Pharmacokinetics-Biopharmaceutics Laboratory, Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland at Baltimore, Health Sciences Facility II, 20 Penn Street, Room 543, Baltimore, MD 21201. E-mail: neddingt{at}rx.umaryland.edu