Enteric polymers as acidifiers for the pH-independent sustained delivery of a weakly basic drug salt from coated pellets.

Weakly basic drugs and their salts exhibit a decrease in aqueous solubility at higher pH, which can result in pH-dependent or even incomplete release of these drugs from extended release formulations. The objective of this study was to evaluate strategies to set-off the very strong pH-dependent solubility (solubility: 80 mg/ml at pH 2 and 0.02 mg/ml at pH 7.

pH-Sensitive polymer blends used as coating materials to control drug release from spherical beads: elucidation of the underlying mass transport mechanisms.

Purpose: To elucidate the drug release mechanisms from pellets coated with pH-sensitive polymer blends.

Methods: Verapamil hydrochloride-loaded beads were coated with various blends of a water-insoluble and an enteric polymer, ethylcellulose:Eudragit L and Eudragit NE:Eudragit L, respectively. Both experimental and theoretical techniques were used to characterize the systems before and upon exposure to 0.

pH-sensitive polymer blends used as coating materials to control drug release from spherical beads: importance of the type of core.

The aim of this study was to coat theophylline-loaded spherical beads with pH-sensitive polymer blends to control the resulting drug release kinetics. Various mixtures of ethylcellulose (water-insoluble) and Eudragit L (methacrylic-acid-ethyl-acrylate-copolymer; water-insoluble/water-soluble below/above pH 5.5) were used as coating materials.

Polymer blends used for the coating of multiparticulates: comparison of aqueous and organic coating techniques.

Purpose: The purpose of this study was to use polymer blends for the coating of pellets and to study the effects of the type of coating technique (aqueous vs. organic) on drug release.

Methods: Propranolol HCl-loaded pellets were coated with blends of a water-insoluble and an enteric polymer (ethyl cellulose and Eudragit L).

Investigating the coating-dependent release mechanism of a pulsatile capsule using NMR microscopy.

Chronopharmaceutical capsules, ethylcellulose-coated to prevent water ingress, exhibited clearly different release characteristics when coated by organic or aqueous processes. Organic-coated capsules produced a delayed pulse release, whereas aqueous-coated capsules exhibited less delayed and more erratic release behaviour. Nuclear magnetic resonance microscopy was used to elucidate the internal mechanisms underlying this behaviour by studying the routes of internal water transport and the timescale and sequence of events leading to the pulse.

Measurement and mapping of pH in hydrating pharmaceutical pellets using confocal laser scanning microscopy.

Purpose: pH modifiers are often used to promote drug solubility/ stability in dosage forms, but predicting the extent and duration of internal pH modification is difficult. Here, a noninvasive technique is developed for the spatial and temporal mapping of pH in a hydrated pharmaceutical pellet, within a pH range appropriate for microenvironmental pH control by weak acids.

Methods: Confocal dual excitation imaging (Ex 488/Ex 568) of pellets containing a single, soluble, pH-sensitive fluorophore with cross-validation from a pH microelectrode.