title: Enhanced oral bioavailability of 2'- beta-fluoro-2',3'-dideoxyadenosine (F-ddA) through local inhibition of intestinal adenosine deaminase.
abstract: OBJECTIVE
  Intestinal enzyme inhibition may be an effective tool to increase the oral bioavailability of compounds that undergo first-pass intestinal metabolism. However, systemic enzyme inhibition may be undesirable and therefore should be minimized. 2-Beta-fluoro-2',3'-dideoxyadenosine (F-ddA) is an adenosine deaminase (ADA) activated prodrug of 2-beta-fluoro-2',3'-dideoxyinosine (F-ddI) with enhanced delivery to the central nervous system (CNS) that has been tested clinically for the treatment of AIDS. Unfortunately, intestinally localized ADA constitutes a formidable enzymatic barrier to the oral absorption of F-ddA. This study explores various factors involved in inhibitor selection and dosage regimen design to achieve local ADA inhibition with minimal systemic inhibition.
  
  
  METHODS
  In situ intestinal perfusions with mesenteric vein cannulation were performed in the rat ileum to determine the lumenal disappearance and venous blood appearance of F-ddA and F-ddI. Coperfusions with the ADA inhibitor erythro9-(2-hydroxy-3-nonyl)adenine [(+)-EHNA] over a range of concentrations were used to monitor inhibitor effects on F-ddA absorption and metabolism.
  
  
  RESULTS
  High concentrations of EHNA in coperfusions with F-ddA completely inhibited intestinal ADA, increasing the permeability coefficient of F-ddA by nearly threefold but producing high systemic inhibition of ADA. Mathematical models were utilized to show that in full-length intestinal perfusions an optimal log mean lumenal EHNA perfusate concentration of 0.5 microg/ml could achieve an intestinal bioavailability of 80% with <20% systemic inhibition.
  
  
  CONCLUSIONS
  Optimizing local enzyme inhibition may require careful selection of a suitable inhibitor, the dose of the inhibitor, and the inhibitor vs. drug absorption profiles.
authors.affiliation: Division of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington 40536, USA.
authors.forename: R T
authors.initials: RT
authors.lastname: DeGraw
authors.forename: B D
authors.initials: BD
authors.lastname: Anderson
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology; D058892:Adenosine Deaminase Inhibitors; D000465:Algorithms; D000818:Animals; D019380:Anti-HIV Agents / Q000737:chemistry / Q000493:pharmacokinetics*; D001682:Biological Availability; D001692:Biological Transport; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D016048:Dideoxyadenosine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000493:pharmacokinetics*; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology*; D007408:Intestinal Absorption / Q000187:drug effects; D007422:Intestines / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D058892:Adenosine Deaminase Inhibitors; D019380:Anti-HIV Agents; D004791:Enzyme Inhibitors; C073072:lodenosine; D016048:Dideoxyadenosine; C010192:9-(2-hydroxy-3-nonyl)adenine; D000225:Adenine