pH-sensitive film coatings: towards a better understanding and facilitated optimization

pH-Responsive Copolymer Films Prepared by Surface-Initiated Polymerization and Simple Modification

We report the preparation of pH-responsive, ester/carboxylic acid random copolymer films via simple modification of poly(norbornene diacyl chloride) (pNBDAC), prepared via surface-initiated ring-opening metathesis polymerization, with mixtures of water and ethanol to form carboxylic acid and ethyl ester side groups. The pNBDAC film serves as a compositionally versatile platform to controllably obtain copolymers with multiple functionalities. In modifying the pNBDAC to form the copolymer film, ethanol exhibits a significantly higher reactivity with acyl chloride groups within the film than does water. The magnitude and range of the pH-responsive performance are highly dependent on the carboxylic acid content in the copolymer films, which demonstrates the effect of film hydrophilicity on the pH-responsive switching of ionic barrier properties. The resistance of the film against ion transfer can be decreased by a factor of 10⁴ through pH change, demonstrating pH-induced switching from hydrophobic and insulating to swollen and ion-permeable films. The interactions of the copolymer films with water at different pH values were also explored. When the copolymer contains 34% carboxylic acids, a 4× greater film thickness is obtained in high pH solution than in low pH solution due to ionically driven water swelling. The reversibility of the pH-responsive performance of these copolymer films is high based on measurements using quartz crystal microbalance with dissipation (QCM-D).

Preparation and evaluation of duloxetine hydrochloride enteric-coated pellets with different enteric polymers

The main purpose of the present study was to prepare duloxetine hydrochloride (DXH) enteric-coated pellets using different enteric polymers. Three layers (drug-loaded layer, barrier layer, and enteric-coated layer) were applied to the inert core pellets, successively. The optimal formulation was manufactured by employing suspension layering method in fluidized bed processor (FBP) with varieties of enteric polymers like Aqoat^® AS-LF, Eudragit^® L30D55 and HPMCP-HP55. The prepared pellets were measured for physical characterization and the in vitro dissolution profile. Scanning electron microscopy (SEM) was conducted to observe the morphology of pellets, and different kinetic models were applied to analyze the release mechanism of Cymbalta^® and home-made pellets. The coating weight gain of enteric-coated layer containing Eudragit^® L30D55, Aqoat^® AS-LF and HP-55 were determined to be 35%, 26% and 24%, respectively. The similarity factors (f₂) of self-made capsules with above polymers and commercially available capsules (Cymbalta^®) were above 50 in the dissolution medium of pH 6.8 phosphate buffer solution (PBS). SEM figures showed the smooth surfaces of self-prepared pellets using Eudragit^® L30D55 and Aqoat^® AS-LF, whereas rough surface was found in the HP-55 pellets at day 0, and an impurity was appearing in the condition of 40 °C/75% relative humidity for 1 month. In conclusion, the pellets prepared by utilizing Eudragit^® L30D55 and Aqoat^® AS-LF were the optimal preparations based on the dissolution profile and stability.

Influence of process parameters on tablet bed microenvironmental factors during pan coating

Recent studies have shown the importance of monitoring microenvironmental conditions (temperature, relative humidity) experienced by the tablet bed during a pan coating process, thereby necessitating the need to understand how various process parameters influence these microenvironmental conditions. The process parameters studied in this work include exhaust air temperature, spray rate, inlet airflow rate, gun-to-bed distance, coating suspension percent solids, and atomization and pattern air pressure. Each of these process parameters was found to have an impact on the tablet bed relative humidity (RH), as measured using PyroButton data logging devices. A higher tablet bed RH was obtained with an increase in spray rate and atomization air pressure and with a decrease in exhaust air temperature, inlet airflow rate, gun-to-bed distance, suspension percent solids, and pattern air pressure. Based on this work, it can be concluded that the tablet bed thermodynamic conditions are a cumulative effect of the various process conditions. A strong correlation between the tablet bed RH and the frequency of tablet coating defect (logo bridging) was established, with increasing RH resulting in a higher percent of logo bridging events.

A review of the advancements in probiotic delivery: Conventional vs. non-conventional formulations for intestinal flora supplementation

Probiotic delivery systems are widely used nutraceutical products for the supplementation of natural intestinal flora. These delivery systems vary greatly in effectiveness to exert health benefits for a patient. Probiotic delivery systems can be categorized into conventional, pharmaceutical formulations, and non-conventional, mainly commercial food-based, products. The degree of health benefits provided by these probiotic formulations varies in their ability to deliver viable, functional bacteria in large enough numbers (effectiveness), to provide protection against the harsh effects of the gastric environment and intestinal bile (in vivo protection), and to survive formulation processes (viability). This review discusses the effectiveness of these probiotic delivery systems to deliver viable functional bacteria focusing on the ability to protect the encapsulated probiotics during formulation process as well as against harsh physiological conditions through formulation enhancements using coatings and polymer enhancements. A brief overview on the health benefits of probiotics, current formulation, patient and legal issues facing probiotic delivery, and possible recommendations for the enhanced delivery of probiotic bacteria are also provided. Newer advanced in vitro analyses that can accurately determine the effectiveness of a probiotic formulation are also discussed with an ideal probiotic delivery system hypothesized through a combination of the two probiotic delivery systems described.

In-line prediction of drug release profiles for pH-sensitive coated pellets

A new method for the prediction of the drug release profiles during a running pellet coating process from in-line near infrared (NIR) measurements has been developed. The NIR spectra were acquired during a manufacturing process through an immersion probe. These spectra reflect the coating thickness that is inherently connected with the drug release. Pellets sampled at nine process time points from thirteen designed laboratory-scale coating batches were subjected to the dissolution testing. In the case of the pH-sensitive Acryl-EZE coating the drug release kinetics for the acidic medium has a sigmoid form with a pronounced induction period that tends to grow along with the coating thickness. In this work the autocatalytic model adopted from the chemical kinetics has been successfully applied to describe the drug release. A generalized interpretation of the kinetic constants in terms of the process and product parameters has been suggested. A combination of the kinetic model with the multivariate Partial Least Squares (PLS) regression enabled prediction of the release profiles from the process NIR data. The method can be used to monitor the final pellet quality in the course of a coating process.

Prednisolone-α-cyclodextrin-star poly(ethylene glycol) polypseudorotaxane with delayed pH-sensitivity as a targeted drug delivery system

The acylation of prednisolone 20-hydrazone with star poly(ethylene glycol) tetracarboxylic acid (M = 20,000) has been used to prepare the corresponding pH-sensitive conjugate. With α-cyclodextrin, this conjugate forms a polypseudorotaxane, which was characterised by means of (1)H NMR spectra, powder X-ray diffraction patterns and STM microscopy. The rate of acid-catalysed hydrolysis of the conjugate was studied under in vitro conditions in model media of hydrochloric acid solutions, phosphate and acetate buffers (pH 2-5.8). The acid-catalysed hydrolysis (at pH 2) of the polypseudorotaxane was ca 3.5 times slower than that of the original conjugate. After 1h in this medium, 86% of the covalently attached prednisolone remained unchanged. The prepared polypseudorotaxane represents a promising peroral transport system of prednisolone with a pH-sensitive linker with delayed acid-catalysed hydrolysis thanks to protection at the molecular level using α-cyclodextrin.

Development of sustained release capsules containing "coated matrix granules of metoprolol tartrate"

The objective of this investigation was to prepare sustained release capsule containing coated matrix granules of metoprolol tartrate and to study its in vitro release and in vivo absorption. The design of dosage form was performed by choosing hydrophilic hydroxypropyl methyl cellulose (HPMC K100M) and hydrophobic ethyl cellulose (EC) polymers as matrix builders and Eudragit® RL/RS as coating polymers. Granules were prepared by composing drug with HPMC K100M, EC, dicalcium phosphate by wet granulation method with subsequent coating. Optimized formulation of metoprolol tartrate was formed by using 30% HPMC K100M, 20% EC, and ratio of Eudragit® RS/RL as 97.5:2.5 at 25% coating level. Capsules were filled with free flowing optimized granules of uniform drug content. This extended the release period upto 12 h in vitro study. Similarity factor and mean dissolution time were also reported to compare various dissolution profiles. The network formed by HPMC and EC had been coupled satisfactorily with the controlled resistance offered by Eudragit® RS. The release mechanism of capsules followed Korsemeyer-Peppas model that indicated significant contribution of erosion effect of hydrophilic polymer. Biopharmaceutical study of this optimized dosage form in rabbit model showed 10 h prolonged drug release in vivo. A close correlation (R(2) = 0.9434) was established between the in vitro release and the in vivo absorption of drug. The results suggested that wet granulation with subsequent coating by fluidized bed technique, is a suitable method to formulate sustained release capsules of metoprolol tartrate and it can perform therapeutically better than conventional immediate release dosage form.

Aplicações farmacêuticas de polímeros

Os polímeros representam uma das classes de materiais mais versáteis disponíveis para aplicações em diversas áreas, inclusive a farmacêutica. Polímeros naturais, naturais modificados e sintéticos são empregados como excipientes farmacêuticos para a formulação de cosméticos e medicamentos de liberação convencional e de liberação modificada. Nos dias atuais, polímeros são desenvolvidos para atuarem como moduladores e direcionadores da liberação de fármacos em sítios específicos no organismo. Polímeros biodegradáveis, bioadesivos, biomiméticos e hidrogéis responsivos têm sido amplamente incluídos em formulações farmacêuticas. Os avanços na idealização de novos Sistemas de Liberação de Fármacos somente são e serão permitidos a partir do desenvolvimento de polímeros projetados especificamente para a área farmacêutica. Neste sentido, o presente artigo visa a revisar e apresentar informações sobre o uso de polímeros em aplicações farmacêuticas que poderão ser úteis no planejamento de novos sistemas com desempenhos superiores.

Prediction of drug release from ethylcellulose coated pellets

The aim of this study was to elucidate the underlying drug release mechanisms in pellets coated with aqueous ethylcellulose dispersion, providing long term stable drug release profiles and containing different types of starter cores. The systems were thoroughly characterized using mechanical analysis; the sensitivity of drug release to the osmolality of the release medium was measured; scanning electron microscopy and optical macroscopy were used to monitor the pellets' morphology and dimensions upon exposure to different media, and drug release was measured from single and ensembles of pellets as well as from thin, free films. All experimental results indicate that diltiazem HCl release from pellets coated with ethylcellulose containing small amounts of poly(vinyl alcohol)-poly(ethylene glycol) graft copolymer is primarily controlled by drug diffusion through the intact polymeric membranes, irrespective of the type of starter core (consisting of microcrystalline cellulose or sugar, optionally coated with ethylcellulose). Importantly, the apparent diffusion coefficient of the drug in the macromolecular networks could easily be determined with thin free films and successfully be used to quantitatively predict the release rate from coated pellets. Thus, based on this knowledge and using the presented mathematical theories the development of new/ optimization of existing controlled drug delivery systems of this type can be significantly facilitated.

Composite microparticle drug delivery systems based on chitosan, alginate and pectin with improved pH-sensitive drug release property

Composite microparticle drug delivery systems based on chitosan, alginate and pectin with improved pH sensitivity were developed for oral delivery of protein drugs, using bovine serum albumin (BSA) as a model drug. The composite drug-loaded microparticles with a mean particle size less than 200mum were prepared by a convenient shredding method. Since the microparticles were formed by tripolyphosphate cross-linking, electrostatic complexation by alginate and/or pectin, as well as ionotropic gelation with calcium ions, the microparticles exhibited an improved pH-sensitive drug release property. The in vitro drug release behaviors of the microparticles were studied in simulated gastric (pH 1.2 and pH 5.0), intestinal (pH 7.4) and colonic (pH 6.0 and pH 6.8 with enzyme) media. For the composite microparticles with suitable compositions, the releases of BSA at pH 1.2 and pH 5.0 could be effectively sustained, while the releases at pH 7.4, pH 6.8 and pH 6.0 increased significantly, especially in the presence of pectinase. These results clearly suggested that the microparticles had potential for site-specific protein drug delivery through oral administration.