Abstract
The influence of drug properties such as solubility and core shape on microencapsulation with ethyl cellulose (EC) by the phase separation method was studied. Drugs having various solubilities from about 1% to 37% in the 1st fluid of the disintegration test in JP (vitamin C, vitamin B6, isoniazid, trimebutine maleate and theophylline) were pulverized, granulated into spherical or cylindrical shapes, and used as core materials to eliminate the influence of crystal shape. To obtain spherical microcapsules (MC) having a uniform wall, various preparation conditions were tested; wall thickness could be adjusted by changing the cooling time. It was found by use of spherical core materials of vitamin C and isoniazid that the permeability constants, Pm, linearly decreased as the wall thickness increased up to 12 μm, and then remained constant. Comparison of microcapsules containing the above five drugs revealed that the content of EC in MC decreased with increasing drug hydrophilicity. The dissolution rates from MC having a wall thickness of 12-15 μm were slower for less water-soluble drugs, though the plots of dissolution percent against the so-called reduced time showed similar dissolution patterns. Pm values were almost the same for all drugs except theophylline. As regards core shape, crystalline material showed the fastest dissolution, followed by cylinder and sphere in that order.
