ethyl-cellulose and acetylcellulose

The objective of this work was the preparation of osmotic tablets using polymer blends of cellulose acetate butyrate (CAB) or ethylcellulose with ammonio methacrylate copolymer (Eudragit® RL). The advantage of these coatings in comparison to the traditionally used cellulose acetate is their solubility in safer organic solvents like ethanol. Polymer films were characterized with respect to their water uptake, dry mass loss, and mechanical properties. The effect of the polymer blend ratio on drug release and on the rupture force of the coating was investigated. In addition, the effect of drug solubility and content, pH and agitation rate of the release medium, and coating level and plasticizer content on the release were studied. With increased Eudragit® RL content in the coating blends, higher medium uptake of the film was observed, resulting in shorter lag times and faster drug release from the osmotic tablets. Replacing ethylcellulose with cellulose acetate butyrate as a coating material led to shorter lag times and faster drug release due to increased film permeability. In addition, CAB-based films had a higher strength and flexibility. The drug release was osmotically controlled and decreased with increasing coating level. It increased with increased drug solubility, plasticizer content, change of buffer species (acetate > phosphate), and decreased coating level. Agitation rate and drug content had no effect on the drug release. A 20% w/w coating level was sufficient for the tablet to tolerate forces of more than five times of the gastric destructive force reported in literature.

Topics: Cellulose; Drug Liberation; Excipients; Osmosis; Plasticizers; Polymethacrylic Acids; Solubility; Tablets

The present study was aimed at developing and evaluating polymeric beads with sustained drug release and prolonged gastric residence. The polymeric beads were prepared by solvent evaporation technique using Cellulose acetate (CA) as matrix former for model drug Ibuprofen (IBF) in 1% aqueous polyvinyl alcohol (PVA) solution as external phase. Effects of various formulation variables like drug-polymer ratio, external phase viscosity, external phase volume, solvent ratio and processing variables like stirring speed, temperature of external phase, stirring time, and drying temperature on properties of beads were accessed. Drug polymer ratio was optimized to maximize the percent yield and drug content. Beads were characterized for shape, size, percent buoyancy, entrapment efficiency, floating time and in-vitro drug release. The scanning electron micrographs show a porous nature of beads thereby enabling them to float. When used alone, CA though formed good beads, drug entrapment efficiency was very low. To increase the drug entrapment, CA was partially substituted with Ethyl cellulose EC (up to 20%) to modulate drug entrapment efficiency and optimize the bead properties including drug release. Beads formed with higher viscous solution either formed agglomerates or dumbbell shaped structures. The optimized batches have uniform size distribution, remained buoyant for more than 18 hours and sustained the drug release up to 10 hours with diffusion through matrix being the main drug releasing mechanism.

Topics: Biological Availability; Cellulose; Delayed-Action Preparations; Drug Delivery Systems; Gastrointestinal Agents; Ibuprofen; Microscopy, Electron, Scanning; Microspheres; Particle Size; Polyvinyl Alcohol; Solvents; Surface Properties; Temperature; Time Factors; Viscosity

The objective of this study was to assess the in vitro and in vivo degradation properties of macroporous sponges composed of oxidized acetyl-cellulose (AC; 45.000 Mw) and ethyl-cellulose (EC; 50.000 Mw). The sponges were constructed by solvent-casting and particulate-leaching technique using a polymer concentration of 2.5 and 5.0% (w:v), and periodate oxidation. The resulting sponges were: AC2.5, AC5.0, EC2.5 and EC5.0. While AC sponges exhibited a gradual degradation overtime, EC sponges had a very slow in vitro mass loss. In general, sponges made up of 2.5% (w:v) polymer content degraded faster than the ones with 5.0% (w:v). The sponges degraded faster at pH 5.0, compared to pH 6.0 and 7.4 conditions. About 60%, 44% and 31% of dry mass loss was determined for AC2.5 sponges after 60 weeks at pH 5.0, pH 6.0 and pH 7.4 conditions, respectively; thus, ca. 21%, 13% and 12% of dry mass loss from EC2.5 sponges was observed at the same pH conditions, in the same order. The in vivo degradation studies were performed on Wistar rats (n = 24) for a duration of 60 weeks. In general, all sponge implants were well-tolerated by the subjects. While granulation tissue or fibrotic capsule was not formed around the sponges, neovascularization was observed. AC and EC sponges demonstrated an in vivo degradation behavior quite similar to that observed for the in vitro study conducted at pH 5.0 conditions. Histomorphometric analysis revealed that the in vivo degradation of AC2.5 and EC2.5 after 60 weeks was about 47% and 18%, respectively. The results indicate that oxidized acetyl cellulose may be considered as a partially degradable scaffold material for tissue engineering applications.

Topics: Animals; Biodegradation, Environmental; Cellulose; Male; Materials Testing; Rats; Rats, Wistar

The objective of this study was to compare the performance of cellulose acetate (CA) and ethylcellulose (EC)-HPMC combination coatings as semipermeable membranes (SPMs) for osmotic pump tablets (OPTs) of naproxen sodium (NPS) so as to deliver a constant, predetermined amount of drug in solution form over a fixed span of time, independent of external environmental conditions. Osmotic pump tablets were designed with different coating variables and optimized in terms of nature of plasticizer, membrane thickness, and orifice diameter. The effect of insertion of an inner microporous film around the NPS core to minimize deformation of the SPM due to peristaltic movement of the gut was also studied. Osmotic pump tablets composed of membranes with water-soluble plasticizer, propyleneglycol (PG), released drug mainly through diffusion, whereas those designed with CA and EC-HPMC (4:1) coats containing water-insoluble plasticizer, castor oil, released their contents by perfect zero-order kinetics over a prolonged period of time, though the average release rate that could be achieved with the EC-HPMC (4:1) membrane was only about half the rate achieved with the CA membrane for the same membrane thickness. Release rates for both the membranes decreased with increasing membrane thickness and were found to be independent of orifice diameter, agitation intensity, and pH of the dissolution medium.

Topics: Administration, Oral; Anti-Inflammatory Agents, Non-Steroidal; Cellulose; Dosage Forms; Drug Compounding; Excipients; Hypromellose Derivatives; Methylcellulose; Naproxen; Osmosis; Permeability; Tablets

The effects of physical aging on the water permeation of cellulose acetate and ethylcellulose, the mechanical properties of ethylcellulose, and the dissolution property of hydroxypropyl methylcellulose phthalate were investigated. The water permeabilities of cellulose acetate and ethylcellulose and the dissolution rate of hydroxypropyl methylcellulose phthalate were found to decrease with physical aging time after being quenched from above the glass transition temperatures to sub-Tg temperatures. The gradual approach toward thermodynamic equilibrium during physical aging decreases the free volume of the polymers. This decrease in free volume is accompanied by a decrease in the transport mobility, with concomitant changes in those properties of the polymer that depend on it. The effects of long-term aging on the dissolution rate and water permeabilities of these polymers can be estimated from a linear double-logarithmic relationship between the mobility properties and physical aging time. The existence of the linear double-logarithmic relationship can be derived from the Williams-Landel-Ferry equation, the Doolittle equation, Struik's model, and Fujita's relationship between diffusion and free volume.

Topics: Cellulose; Chemistry, Pharmaceutical; Delayed-Action Preparations; Methylcellulose; Permeability; Polymers; Solubility; Tablets; Temperature; Time Factors