Doris A. Wall

pH-Dependent Dissolution in Vitro and Absorption in Vivo of Weakly Basic Drugs: Development of a Canine Model

No HeadingPurpose.The aim of this research was to develop a pH-dependent canine absorption model for studying pH effect on both dissolution in vitro and pharmacokinetics in vivo using the weak bases ketoconazole and dipyridamole as model drugs.Methods.Ketoconazole and dipyridamole pH-dependent dissolution profiles in vitro were determined by dissolution test at different pH values using USP apparatus II and an Opt-Diss Fiber Optic UV System. In vivo absorption studies for ketoconazole and dipyridamole were performed with crossover design in three groups of beagle dogs under control (no treatment), pentagastrin, and famotidine treatments. Ketoconazole and dipyridamole plasma concentrations were quantified by gradient high performance liquid chromatography mass spectroscopy (HPLC MS/MS). Pharmacokinetic parameters were determined from individual plasma concentration vs. time profiles.Results.Ketoconazole and dipyridamole displayed pH-dependent dissolution. Increasing the pH of the dissolution medium from 1.2 to 6.8 reduced the extent of dissolution of ketoconazole and dipyridamole at 1 h by 96% and 92%, respectively. In vivo studies in dogs under control (no treatment), pentagastrin, and famotidine treatments show marked differences in systemic ketoconazole and dipyridamole exposure. Area under the concentration-time curve (AUC) increased more than 4-fold as compared to control group, whereas it increased nearly 30-fold for ketoconazole and 9-fold for dipyridamole with pentagastrin (gastric pH ∼2–3) as compared to famotidine (gastric pH ∼5–7.5) treatment.Conclusions.This work demonstrates a pH-dependent dissolution in vitro and absorption in vivo for the weak bases ketoconazole and dipyridamole independent of food effects. This model is useful to examine pH-dependent effects on oral drug absorption and for screening formulations to overcome the pH dependency.

Lack of Effect of Ammonium Glycyrrhizinate on the Morphology of Ovine Nasal Mucosa in Vitro

Glycyrrhetinic acid derivatives are reported to be nasal absorption promoters (1). Effects of ammonium glycyrrhizinate (AMGZ) on the in vitro morphology of ovine nasal mucosa were therefore examined by light and electron microscopy. Nasal mucosa was stripped from the submucosa and mounted in Ussing chambers. Exposure of the apical surface to 2% ammonium glycyrrhizinate (24 mM) for 90 min caused no histopathological changes to the nasal epithelium. Epithelial integrity remained intact as evidenced by the continued presence of morphologically intact junctional complexes. No sloughing of the epithelial layer from the basement membrane was observed, and cilia and microvilli were not affected by treatment with AMGZ. The results indicate that short-term exposure in vitro to ammonium glycyrrhizinate caused no overt morphological damage to ovine nasal mucosa.

Expression Profile of Drug and Nutrient Absorption Related Genes in Madin-Darby Canine Kidney (MDCK) Cells Grown under Differentiation Conditions

The expression levels of genes involved in drug and nutrient absorption were evaluated in the Madin-Darby Canine Kidney (MDCK) in vitro drug absorption model. MDCK cells were grown on plastic surfaces (for 3 days) or on Transwell® membranes (for 3, 5, 7, and 9 days). The expression profile of genes including ABC transporters, SLC transporters, and cytochrome P450 (CYP) enzymes was determined using the Affymetrix® Canine GeneChip®. Expression of genes whose probe sets passed a stringent confirmation process was examined. Expression of a few transporter (MDR1, PEPT1 and PEPT2) genes in MDCK cells was confirmed by RT-PCR. The overall gene expression profile was strongly influenced by the type of support the cells were grown on. After 3 days of growth, expression of 28% of the genes was statistically different (1.5-fold cutoff, p < 0.05) between the cells grown on plastic and Transwell® membranes. When cells were differentiated on Transwell® membranes, large changes in gene expression profile were observed during the early stages, which then stabilized after 5–7 days. Only a small number of genes encoding drug absorption related SLC, ABC, and CYP were detected in MDCK cells, and most of them exhibited low hybridization signals. Results from this study provide valuable reference information on endogenous gene expression in MDCK cells that could assist in design of drug-transporter and/or drug-enzyme interaction studies, and help interpret the contributions of various transporters and metabolic enzymes in studies with MDCK cells.

Effect of Delivery Route on Pulmonary Response to Oncostatin M

The effect of delivery route on lung tissue response to oncostatin M (OM) was evaluated in isolated perfused rat lung (IPRL) and normal human bronchial epithelial cell line BEAS-2B in vitro models. In this study, the extent of induction of the cytokine IL-6 by OM was examined as evidence for local pharmacological activity in response to OM in lung tissue. OM stimulated dose-dependent release of IL-6 in both BEAS-2B cells and IPRL after exposure of either the apical (AP) or basolateral (BL) side of the epithelium. The increase in IL-6 was rapid, beginning 2 h after dosing, and sustained over 48 h. Similar amounts of IL-6 were released to both AP and BL sides of BEAS-2B cells, regardless of the side of OM dosing. However, in IPRL the extent of response of IL-6 induction to OM was always higher at the dosing side. In addition, airway dosing of OM resulted in an overall lower IL-6 response than perfusate dosing, which may result from the low rate of OM transport (<1%/h) across pulmonary epithelium. We conclude that the route of delivery significantly affects the overall extent of the pharmacological response to OM, with a lesser and more localized response after airway delivery to the lung.