Accelerated in vitro release methods for characterizing biodegradable microspheres

摘要

The first hypothesis of this research was that accelerated or short-term release can be correlated with real-time (37°C) or long-term release. Such correlation would allow accelerated release to be used as a quality control tool for the approval of clinical and commercial batches. The second hypothesis was that accelerated release of drug from microspheres, which can be described by a mathematical model, will aid in the prediction of real-time release. The objectives to accomplish these hypotheses were accomplished as described below.;The first objective was to select an appropriate method to study in vitro peptide release from biodegradable microspheres. A comprehensive search of the literature revealed the disadvantages of the existing methods which necessitated method development. A novel dialysis method was developed using a commercially available dialyzer and peptide diffusion at varying temperatures and different buffers was studied. Peptide diffusion was rapid at the temperatures studied with no detectable binding to the dialysis membrane enabling assessment of initial burst release from peptide-loaded microspheres. Other advantages of the dialyzer were ease of set-up and sampling and also, reusability of the membrane, which made it cost-effective.;The second objective of this research was to accelerate peptide release from microspheres and correlate it with real-time release at 37°C in 0.1M phosphate buffered saline (PBS) pH 7.4 using the dialysis method. Peptide release was accelerated using elevated temperatures (50--60°C) and Acetate buffer pH 4.0 and correlated well with real-time release at 37°C, indicating the predictive nature of accelerated or short-term release. A model dependent approach (Weibull equation) was used to analyze in vitro release data at 37°C and the elevated temperatures. Various mechanistic and empirical models were evaluated prior to selection of the Weibull equation, which was modified to describe the sigmoidal tri-phasic release of Leuprolide from PLGA microspheres. A comparison of model parameters 'alpha' and 'beta' revealed that accelerated release at 55°C in 0.1M PBS pH 7.4 and 50°C in 0.1M acetate buffer pH 4.0 correlated best with real-time release at 37°C.;The third objective assessed the use of accelerated release as a quality control tool for approval of clinical or commercial batches. Two batches of peptide-loaded microspheres differing in particle size (formulation variants) were prepared and short-term release compared with a standard microsphere formulation at 55°C in 0.1M PBS pH 7.4. Data analysis using the Weibull equation was able to discriminate the rate and shape of the release profiles for the batches. In addition, good reproducibility was obtained for release within and between batches, suggesting that accelerated release could be used as a discriminatory quality control tool for batch approval.