A simple spectroscopic method for the determination of the release kinetics of drugs from PHB

A simple method is proposed for the determination of the release kinetics of small molecular weight drugs from amorphous PHB. The method uses the hipsochromic shift of the absorbance of active molecules caused by changes in the UV–Vis spectra as an effect of changing environment. Fuchsine with a strong hypsochromic shift was used as model drug in the experiments. A simple experimental setup was created which consists of the positioning of a thin PHB film into the center of the cell of a spectrometer. The light goes through the film and the surrounding solution and records their spectra simultaneously. The arrangement makes possible the quantitative determination of the dissolution of the drug without any further interference. The solution of Fick's second law under the initial and boundary conditions of the experimental setup and the numerical solution of the equation allow the quantitative analysis of the experimental results and the prediction of release kinetics. Excellent agreement was found between prediction and the experimental results. The approach made possible also the determination of the diffusion coefficient of the model drug in amorphous PHB. The developed method can be used for all polymers and with all drugs, which show sufficiently strong hypsochromic shift during their transfer from the polymer to the solution phase.