Use of Modified Ethylcellulose Lattices for Microporous Coating of Osmotic Tablets

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Abstract
Commercially available lattices are often used to coat nonpareils or beads. Drug release occurs via diffusion through the polymer coating. Adequate release rates may be achieved with small particles because the surface area is large. However, tablets coated with unmodified lattices have exceedingly slow release rates. Therefore, a pore-forming agent, urea, was added to a commercially available ethyl cellulose latex, Aquacoat, to increase the release rate of drugs from coated osmotic tablets. Modified lattices were used to coat KC1 and diltiazem · HC1 tablets. Release of KC1 and diltiazem into water or buffer solutions was determined in a standard U.S.P. dissolution apparatus. Rates varying from 1 to 100% release in 12 hr were obtained by varying the coating thickness, pore-former level, and plasticizer type and concentration. Scanning electron microscopy (SEM) showed that the urea was eluted from the coat in aqueous solution leaving a porous coating. Coat burst strengths were dependent on the coat thickness and the concentrations of pore former and plasticizer. Hence, modified lattices hold potential for use as coatings for controlled release osmotic formulations.

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