The objective of this investigation is to develop a multi-unit sustained release dosage form of a water soluble drug from a completely aqueous environment avoiding the use of any organic solvent. The drug was complexed with resin and calcium alginate or polyethyleneimine-treated calcium alginate beads loaded with the resinate were prepared by a ionic/polyelectrolyte complexation method. The effect of different formulation variables on the characteristics of the beads was investigated. Although the drug release from spherical and smooth-surfaced calcium alginate beads in both acidic and alkaline dissolution media were slower than those obtained from plain resinate, none of the variables were found to prolong the drug release considerably due to rapid swelling and disintegration of calcium alginate beads in alkaline medium. On the other hand, drug release from polyethyleneimine-treated calcium alginate beads in acidic medium did not increase appreciably following a burst release. However, in alkaline medium, the drug release was found to increase gradually and extend over a different period of time depending on the intensity of polyethyleneimine treatment. Scanning electron micrographs revealed the formation of a dense membrane around the resinate-loaded calcium alginate matrix. The membrane appeared to be responsible for reduced swelling and protracted disintegration of the beads resulting in slow release of the drug. The results indicate that sustained release of a water soluble drug from polyethyleneimine-treated calcium alginate beads could be achieved by adjusting the formulation variables.
Studies were made of pulmonary diffusion capacity and oxygen transport before and after an expedition to altitudes at and above 4900 m. Maximum power (Pmax) and maximal oxygen uptake (VO2max) were measured in 11 mountaineers in an incremental cycle ergometer test (25W.min-1) before and after return from basecamp (30 days at 4900 m or higher). In a second test, cardiac output (Qc) and lung diffusion capacity of carbon monoxide (DL,cg) were measured by acetylene and CO rebreathing at rest and during exercise at low, medium and submaximal intensities. After acclimatization, VO2max and Pmax decreased by 5.1% [from 61.0 (SD 6.2) to 57.9 (SD 10.2) ml.kg-1, n.s.] and 9.9% [from 5.13 (SD 0.66) to 4.62 (SD 0.42) W.kg-1, n.s.], respectively. The maximal cardiac index and DL,cg decreased significantly by 15.6% [14.1 (SD 1.41) 1.min-1.m-2 to 11.9 (SD 1.44)1.min-1.m-2, P < 0.05] and 14.3% [85.9 (SD 4.36) ml.mmHg-1. min-1 to 73.6 (SD 15.2) ml.mmHg-1.min-1, P < 0.05], respectively. The expedition to high altitude led to a decrease in maximal Qc, oxygen uptake and DL,cg. A decrease in muscle mass and capillarity may have been responsible for the decrease in maximal Qc which may have resulted in a decrease of DL,cg and an increase in alveolar-arterial oxygen difference. The decrease in DL,cg especially at lower exercise intensities after the expedition may have been due to a ventilation-perfusion mismatch and changes in blood capacitance. At higher exercise intensities diffusion limitation due to reduced pulmonary capillary contact time may also have occurred.
The purpose of this study was to examine the suitability of polystyrene-coated (PS-coated) microcapsules of drug-resin complex for achieving prolonged release of diltiazem-HCl, a highly water-soluble drug, in simulated gastric and intestinal fluid. The drug was bound to Indion 254, a cation-exchange resin, and the resulting resinate was microencapsulated with PS using an oil-in-water emulsion-solvent evaporation method. The effect of various formulation parameters on the characteristics of the microcapsules was studied. Mean diameter and encapsulation efficiency of the microcapsules rose with an increase in the concentration of emulsion stabilizer and the coat/core ratio, while the same characteristics tended to decrease with an increase in the volume of the organic disperse phase. The desorption of drug from the uncoated resinate was quite rapid and independent of the pH of the dissolution media. On the other hand, the drug release from the microcapsules was prolonged for different periods of time depending on the formulation parameters and was also found to be independent of the pH of the dissolution media. Both the encapsulation efficiency and the retardation of drug release were found to be dependent on the uniformity of coating, which in turn was influenced by the formulation parameters. Kinetic studies revealed that the desorption of drug from the resinate obeyed the typical particle diffusion process, whereas the drug release from the microencapsulated resinate followed the diffusioncontrolled model in accordance with the Higuchi equation. PS appeared to be a suitable polymer to provide prolonged release of diltiazem independent of the pH of the dissolution media.
Propranolol-HCl, a water soluble drug, was bound to Indion 254, a cation exchange resin, and the resulting resinate was microencapsulated with polystyrene using an oil-in-water emulsion-solvent evaporation method with a view to achieve prolonged drug release in simulated gastric and intestinal fluid. The effect of various formulation parameters on the characteristics of the microcapsules was studied. The diameter of the resinate-loaded polystyrene microcapsules increased with increase in the concentration of emulsion stabilizer and coat/core ratio and decreased with increase in the volume of organic disperse phase. The variation in the size of the microcapsules appeared to be related with the inter-facial viscosity which was influenced by the viscosity of both the aqueous dispersion medium and the organic disperse phase. The resinate encapsulation efficiency and hence the drug entrapment efficiency of the microcapsules increased with increase in the concentration of emulsion stabilizer and coat/core ratio and decreased with increase in the volume of organic disperse phase. These characteristics were found to depend on the extent of formation of fractured microcapsules and subsequent partitioning of the resinate into the aqueous dispersion medium. The degree of fracture on the microcapsules depended on the viscosity of the aqueous dispersion medium and the organic disperse phase. The uncoated resinate discharged the drug quite rapidly following the typical particle diffusion process. Although the desorption of the drug from the resinate was independent of pH of the dissolution media, increase in ionic strength increased the drug desorption. On the other hand, release of drug from the coated resinate was considerably prolonged and followed a diffusion controlled model. The prolongation of drug release was dependent on the uniformity of coating which was influenced by the formulation parameters. The drug release from the microcapsules was also found to be independent of pH of the dissolution media and increased with increase in ionic strength. The pH-independent release of the drug from both the uncoated and microencapsulated resinate was due to pH-independent solubility of the drug and high equilibrium concentration of the resinate in both the dissolution media. Polystyrene appeared to be a suitable polymer to provide prolonged release of propranolol independent of pH of the dissolution media.
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