Alterations in pentobarbital pharmacokinetics in response to parenteral and enteral alimentation in the rat.

Recent in vitro observations suggest that the intestine, in addition to the liver, may be an important organ of first-pass drug metabolism. While a variety of changes in intestinal morphology and function in response to continuous parenteral and enteral nutrition have been documented, the effect of different routes of alimentation on intestinal drug metabolism has not been previously investigated. Objectives of this study were to assess the contribution of intestinal pentobarbital metabolism to overall in vivo pentobarbital pharmacokinetics in the rat and to determine if differences in pentobarbital pharmacokinetics were seen between parenterally and enterally nourished animals. After 7 days of continuous infusion of amino acid-glucose mixture via a gastric or jugular vein catheter, pharmacokinetic parameters were determined after 40 mg/kg of pentobarbital was given orally or into the portal or femoral vein. Reduced systemic availability of pentobarbital after oral administration as compared to portal vein injection was seen in both alimentation groups indicating that significant intestinal metabolism of pentobarbital occurred in vivo. Total area under the pentobarbital plasma concentration-time curve was significantly greater in parenterally nourished animals as compared with enterally alimented animals after oral, portal vein and systemic vein drug administration. Differences in pentobarbital, pharmacokinetics between the two alimentation groups appeared to be primarly due to effects on hepatic pentobarbital metabolism. While the mechanism producing these changes has not been defined, differences in gut hormones release and/or pancreatic secretion in response to the two routes of alimentation may be contributory. The widespread use of enteral and parenteral alimentation in clinical medicine suggests that studies to determine if nutrition route of administration similarly influences drug metabolism in humans may be indicated.