James Shunnan Chu

Effect of colonic lactulose availability on the timing of drug release onset in vivo from a unique colon-specific drug delivery system (CODES).

AbstractPurpose. To test the hypothesis that the onset of drug release in vivo from a unique colon-specific drug delivery system (CODES™) would depend on the colonic availability rate of lactulose. The site specificity of drug release in canine GI tract was also estimated. Methods. CODES™ tablets were prepared by tableting the granulation of acetaminophen and lactulose, followed with film coating. The pharmacokinetic performance of different CODES™ formulations was evaluated in six beagle dogs under fasted conditions. The release of acetaminophen and lactulose was also characterized in vitro. Results. The onset of acetaminophen release in beagle dogs was found to be dependent on the coating level of Eudragit E and lactulose loading in the core tablet. At Eudragit E coating levels of 4%, 8%, and 12% (coating weight gain), the onset of in vivo drug release occurred 5.5 (±1.9) h, 4.8 (±1.0) h. and 7.5 (±1.0) h, respectively, after dosing. A similar trend was observed when the loading of lactulose in the core tablet decreased from 78% to 58% and 38%. However, the rate and extent of acetaminophen absorption did not vary significantly in each situation based on the values of AUC and Cmax. Conclusions. The onset of drug release in vivo from CODES™ tablets is predominantly dependent on colonic availability rate of lactulose because drug release from this system is triggered by localized drop of colonic pH from the fermentation of lactulose.

Viscoelastic Properties of Polyacrylic Acid Gels in Mixed Solvents

The objective of this study is to investigate the viscoelastic properties of Carbopol 934P polymeric systems in a variety of mixtures of pharmaceutical solvents. Carbopol 934P neutralized with a 1:1 equivalent ratio of triethanolamine was dissolved in various binary or ternary solvent mixtures consisting of propylene glycol, glycerol formal, and water. Dynamic moduli G′ and G″, complex viscosities, η′ and η″, and loss tangent, tanδ, were examined over a frequency range of 10-3 to 10 Hz using an oscillatory viscoelastic rheometer at 30°C. The results indicated that for 0.5-1.5 wt% neutralized Carbopol in ternary mixtures, G′ and G″ increased by 3-4 orders of magnitude and the phase angle decreased from 80 to 25° when the water content in the solvent mixture increased from 10 to 80 wt%. These studies also indicated that the addition of water to nonaqueous Carbopol 934P polymer systems transforms them from low-viscosity solutions to gels with significant elastic behavior involving physical interaction and entanglement of polymer segments with solvents.

Mixture Experimental Design in the Development of a Mucoadhesive Gel Formulation

The objective of the present study is to apply response surface methodology to the design and analysis of composite experiments containing independent covariate(s). The approach is illustrated here by the study of viscosity characteristics of a polymeric mucoadhesive formulation in multicomponent solvent vehicles. The nonaqueous formulation will produce a gel network with significant rheological change when in contact with body fluids. The process of water inclusion will induce not only solvent compositional change of the mixture but also concomitant dilution of the polymer concentration. To study the viscosity change over the solvent compositions and polymeric concentrations of interest, an experimental design is utilized consisting of a 10-point simplex-centroid lattice augmented with three interior points at each polymeric concentration. The contour patterns are compared with the experimental, data using the variance and lack of fit, starting with the Scheffe linear model and building up to the full cubic model including the covariate terms. The fitted model provides information needed to predict optimum formulations, i.e., initial viscosity of less than 100 cP, but yielding rheological profiles commensurate with high degrees of substantivity when diluted with water. For illustrative purposes, the Carbopol resins neutralized with a 1:1 molar equivalent ratio of triethanolamine in three primary solvents, propylene glycol, glycerol formal, and water, were chosen for this study.

Viscometric study of polyacrylic acid systems as mucoadhesive sustained-release gels.

This report describes a novel nonaqueous polymeric formulation that exhibits low-viscosity fluid behavior for ease of spraying with conventional nebulizer, which when sprayed into the nasal cavity, transforms to a high-viscosity gel for efficient retention and drug absorption. The transformation occurs because of the rheological changes induced by a change in the solvent composition of the polymeric formulation in the moist nasal cavity. Such a rheological change would then facilitate enhanced residence time of the drug at the site of administration in order to avoid drainage losses. This study reports the results of the effects of a variety of factors such as solvent composition and polymer concentration on the rheological properties of a polyacrylic acid polymer. An attempt to correlate viscosity enhancement effects with enhanced and sustained-release behavior of propranolol, a drug that undergoes extensive first-pass effects, from such formulations via nasal administration in beagle dogs is also described.