Placebo granules as cores for timed release drug delivery systems

Abstract

A drug delivery system is proposed constituted of spherical placebo granules as cores with polymeric surface films containing drug. This timed release dosage form has been prepared by means of a fluidized bed coating technique using ethyl cellulose as the polymeric film and caffeine and salicylic acid as model drugs. The release of the drugs from the dosage form (a) at different drug concentrations and (b) into solutions of different pH showed that drug release was linearly related to the square root of time. Good agreement was found between the theoretical release rate of caffeine, calculated according to Higuchi's equation for a homogenous matrix using membrane permeation parameters measured on linear films, and the experimental results in the case of low drug concentrations. Deviation of the release rate from the homogenous model at high drug concentrations could be explained by crystallization of the drug from the film.

Heterogeneous model of drug release from polymeric matrix

“…Friedman et al (9) prepared timed-release dosage forms using ethylcellulose as the polymeric matrix and salicylic acid and caffeine as model drugs. They determined drug release rates for different initial drug concentrations, and their experimental results are presented in Tables V and VI.…”

Polysorbate 20 as a drug release regulator in ethyl cellulose film coatings

“…First order kinetics, the theoretical equation dealing with the release mechanism of film-coated tablets and free films, do not apply when the film changes with time (Goldman 1970;Shah & Sheth 1972;Lee & Robinson 1978;Friedman et al 1979;Lippold & Forster 1981;Donbrow & Benita 1982) and, in some cases, zero order release kinetics can be obtained with appropriate changes in the coat. Leaching of polysorbate 20 changed the coat during the dissolution test, which may be a reason for zero order kinetics.…”