Friedman M, Donbrow M, Samuelov Y
J Pharm Pharmacol. 1979 Jun;31(6):396-9. doi: 10.1111/j.2042-7158.1979.tb13531.x.
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.
提出了一种药物递送系统，该系统由球形安慰剂颗粒作为核心，其表面为含有药物的聚合物薄膜。这种定时释放剂型是通过流化床包衣技术制备的，使用乙基纤维素作为聚合物薄膜，咖啡因和水杨酸作为模型药物。药物从剂型中的释放情况：(a) 在不同药物浓度下；(b) 在不同pH值的溶液中，结果表明药物释放与时间的平方根呈线性关系。对于低药物浓度的情况，根据Higuchi方程，利用在线性薄膜上测得的膜渗透参数计算出的咖啡因理论释放速率与实验结果之间具有良好的一致性。在高药物浓度下，释放速率偏离均匀模型的情况可以用药物从薄膜中结晶来解释。
