Bimodal release of theophylline from "seed-matrix" beads made of acrylic polymers

Coatings of Eudragit® RL and L-55 Blends: Investigations on the Drug Release Mechanism

In a previous study, generally lower drug release rates from RL:L55 blend coated pellets in neutral/basic release media than in acidic release media were reported. The aim of this study was to obtain information on the drug release mechanism of solid dosage forms coated with blends of Eudragit® RL (RL) and Eudragit® L-55 (L55). Swelling experiments with free films were analyzed spectroscopically and gravimetrically to identify the physicochemical cause for this release behavior. With Raman spectroscopy, the swelling of copolymer films could be monitored. IR spectroscopic investigations on RL:L55 blends immersed in media at pH 6.8 confirmed the formation of interpolyelectrolyte complexes (IPECs) that were not detectable after swelling in hydrochloric acid pH 1.2. Further investigations revealed that these IPECs decreased the extent of ion exchange between the quaternary ammonium groups of RL and the swelling media. This is presumably the reason for the previously reported decreased drug permeability of RL:L55 coatings in neutral/basic media as ion exchange is the determining factor in drug release from RL coated dosage forms. Gravimetric erosion studies confirmed that L55 was not leached out of the film blends during swelling in phosphate buffer pH 6.8. In contrast to all other investigated films, the 4:1 (RL:L55) blend showed an extensive swelling within 24 h at pH 6.8 which explains the reported sigmoidal release behavior of 4:1 blend coated pellets. These results help to understand the release behavior of RL:L55 blend coated solid dosage forms.

Effect of the dispersion of Eudragit S100 powder on the properties of cellulose acetate butyrate microspheres containing theophylline made by the emulsion-solvent evaporation method

The dispersion/incorporation of Eudragit S100 powder as a filler in cellulose acetate butyrate (CAB-551-0.01) microsphere containing theophylline was investigated as a means of controlling drug release. Microspheres of CAB-551-0.01 of different polymer solution concentrations/viscosities were prepared (preparations Z(0), Z(A), Z(B) and Z(C)) and evaluated and compared to microspheres of a constant concentration of CAB-551-0.01 containing different amounts of Eudragit S100 powder as a filler (preparations X(A), X(B) and X(C)). The organic solvent acetonitrile used was capable of dissolving the matrix former CAB-551-0.01 only but not Eudragit S100 powder in the emulsion-solvent evaporation method. The CAB-551-0.01 concentration in Z(A), Z(B) and Z(C) was equal to the total polymer concentration (CAB-551-0.01 and Eudragit S100 powder) in X(A), X(B) and X(C), respectively. Scanning electron microscopy (SEM) was used to identify microspheres shape and morphology. In vitro dissolution studies were carried out on the microspheres at 37 degrees C (+/-0.5 degrees C) at two successive different pH media (1.2 +/- 0.2 for 2 h and 6.5 +/- 0.2 for 10 h). Z preparations exhibited low rates of drug release in the acidic and the slightly neutral media. On the other hand, X preparations showed an initial rapid release in the acidic medium followed by a decrease in the release rate at the early stage of dissolution in the slightly neutral pH which could be due to some relaxation and gelation of Eudragit S100 powder to form a gel network before it dissolves completely allowing the remained drug to be released.

The pH-dependent biphasic release of azidothymidine from a layered composite of PVA disks and P(MMA/MAA) spheres

A composite device was developed to provide a biphasic drug release using poly(vinyl alcohol) (PVA) and poly(methylmethacrylate-co-methacrylic acid) (P(MMA/MAA)) spheres. Azidothymidine (AZT), an anti-HIV agent with a short biological half-life, was used as the model drug. Dynamic and equilibrium swelling of the polymers, and kinetics of AZT release from these polymers were determined in pH 1.2 and 6.8 buffer solutions. The swelling of PVA and release of AZT from PVA disks were fast and nearly pH-independent, whereas the swelling behavior and drug release kinetics of P(MMA/MAA) spheres were strongly pH-dependent. A swelling interface number for the spheres at pH 6.8 was determined to be Sw&z.Lt;1 and time dependent. Nevertheless, Fickian diffusion might also contribute to the drug release in this system. The composite disks consisting of PVA matrix and P(MMA/MAA) spheres provided prolonged (over 20 h) and more steady release profiles, differing profoundly from individual components. Such release profiles resulted from the second phase release at pH 6.8 and the presence of PVA layer. The relative drug loading in the matrix could be tailored to produce release profiles varying from a distinct bimodal release to a pseudo zero-order release with an initial burst.

Synthesis and characterization of surface-hydrophobic ion-exchange microspheres and the effect of coating on drug release rate

Biodegradable, dextran-based ion-exchange microspheres (IE-MS) have been used for localized delivery of anticancer drugs and chemosensitizers. Because of their hydrophilic nature, the IE-MS release their payload quickly. The purpose of this work was to develop an IE-MS system that could provide a broad range of release rates for in vitro and in vivo applications. Sulfopropylated dextran microspheres (SP C25 MS) were surface-modified by acylation. These hydrophobically modified sulfopropylated dextran microspheres (HM-MS) were further coated with the cationic acrylic polymer Eudragit RL100 (EU-MS). The changes in chemical composition after the surface modification and coating were characterized by X-ray photoelectron spectroscopy. The effects of the modification and coating on the surface hydrophobicity, equilibrium swelling, surface morphology, and drug loading capacity were investigated. The HM-MS showed little change in swelling and functionality, despite significantly increased affinity to oil and carbon content on the surface. The coated microspheres (EU-MS) exhibited a profoundly decreased swelling ratio, an even higher affinity to oil, a higher loading capacity, and a lower drug release rate. Through further coating of the EU-MS with different amounts of corn oil, the rate of drug release could be tailored to cover a relatively wide range. These results suggest that a versatile delivery system with various release profiles can be prepared by a combination of hydrophobic modification, polymer coating, and oil coating.