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Date of Award

2007

Document Type

Dissertation - Pacific Access Restricted

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Pharmaceutical and Chemical Sciences

First Advisor

Bhaskara Jasti

First Committee Member

Xiaoling Li

Second Committee Member

John Crison

Third Committee Member

Timothy Smith

Fourth Committee Member

Miki Park

Abstract

Drugs exhibiting decreased extent of absorption in the fed state administration when compared to the fasted state administration are termed to exhibit a negative food effect. The known causes for negative food effects are luminal degradation and complexation to metal ions/Ca 2+ . For the drugs that do not undergo GI degradation and metal ion complexation, different factors were attributed to cause negative food effects, which are inconclusive. The objectives of this investigation were; to identify the physicochemical and physiological changes between fasted and fed states and their role in causing negative food effects; to develop an empirical model that correlates the biopharmaceutical properties of molecules to negative food effects; and translate the empirical model to a mechanistic model and explain the mechanisms of negative food effects for drugs that do not have clearly defined mechanisms of negative food effects. The important physicochemical change in the upper intestine was identified to be pH. The pH of the upper intestine in the fasted state is typically 6.5, whereas, the overall post-prandial pH after a standard meal in the duodenum is 5.4 (5.0 − 5.7) and the jejunal pH is 4.7 owing to the emptying of acidic chyme. Negative food effect drugs exhibited incomplete GI absorption, low Log P values and low apical to basolateral Caco-2 permeabilities. Acidic/basic drugs exhibiting either negative food effects or no food effects with a molecular size range of 200–450 Da and no physiological effects (such as secretions and motility) were selected from the literature. Multiple linear regression analysis using five drugs exhibiting negative food effects and seven drugs exhibiting no food effects indicated that, percent food effects correlated to acidic/basic dissociation constants (Ka/Kb) and to Caco-2 permeability (R 2 = 0.9114, Power ≈ 1 and p < 0.00002). A mathematical model, adopted to understand the mechanisms of negative food effects suggested that, lowering of permeability or solubility of the model compounds at the lower pH of the postprandial upper intestinal state may contribute to their negative food effects. Finally, this model was found to be useful in predicting negative food effects using in situ rat permeability values.

Pages

170

ISBN

9780549422341

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