Characterization of the Physiological Spaces and Distribution of Tolbutamide in the Perfused Rat Pancreas

Changes in antibiotic distribution due to pancreatitis

This work sought to define how pancreatitis affected antibiotic distribution in a perfused rat pancreas model. The distribution kinetics of four antibiotics were examined in control animals and animals with pancreatitis. Meropenem and piperacillin distributed into the extracellular space, and their distribution kinetics were unaffected by pancreatitis. In contrast, in pancreatic cells from animals with pancreatitis, ciprofloxacin showed a reduced uptake and clindamycin showed a reduced distribution.

Drug structure-transport relationships

Malcolm Rowland has greatly facilitated an understanding of drug structure–pharmacokinetic relationships using a physiological perspective. His view points, covering a wide range of activities, have impacted on my own work and on my appreciation and understanding of our science. This overview summarises some of our parallel activities, beginning with Malcolm’s work on the pH control of amphetamine excretion, his work on the disposition of aspirin and on the application of clearance concepts in describing the disposition of lidocaine. Malcolm also spent a considerable amount of time developing principles that define solute structure and transport/pharmacokinetic relationships using in situ organ studies, which he then extended to involve the whole body. Together, we developed a physiological approach to studying hepatic clearance, introducing the convection–dispersion model in which there was a spread in blood transit times through the liver accompanied by permeation into hepatocytes and removal by metabolism or excretion into the bile. With a range of colleagues, we then further developed the model and applied it to various organs in the body. One of Malcolm’s special interests was in being able to apply this knowledge, together with an understanding of physiological differences in scaling up pharmacokinetics from animals to man. The description of his many other activities, such as the development of clearance concepts, application of pharmacokinetics to the clinical situation and using pharmacokinetics to develop new compounds and delivery systems, has been left to others.

Sulphonylurea physicochemical-pharmacokinetic relationships in the pancreas and liver

This study examined the physicochemical-pharmacokinetic relationships for the sulphonylureas in the perfused rat pancreas and liver. Multiple indicator dilution studies were conducted with bolus injections of tolbutamide, chlorpropamide, gliclazide, glipizide, glibenclamide and glimepiride, and a reference marker albumin, in the perfused pancreas and liver. Individual solute pharmacokinetics were analysed using nonparametric moment analysis and nonlinear regression assuming a physiologically based pharmacokinetic model. All solutes had similar shaped outflow concentration-time profiles in both the pancreas and liver, but varied in extraction. Negligible drug extraction was evident in the pancreas. Hepatic extraction ranged from 0.03 (tolbutamide) to 0.52 (glibenclamide) and could be related to solute lipophilicity and perfusate protein binding. The sulphonylurea mean transit times in both the pancreas and liver varied four- and ninefold respectively and were related to the lipophilicity and perfusate protein binding of the drug. The permeability surface area product of sulphonylureas from the perfusate into the organs were greater in the liver and were mainly determined by lipophilicity (pancreas, r2 = 0.89; liver, r2 = 0.80). The distribution of the sulphonylureas in both the perfused pancreas and perfused liver was dependent on their lipophilicity and perfusate protein binding.