CHARACTERIZING DRUG-RELEASE PROCESSES WITHIN CONTROLLED-RELEASE DOSAGE FORMS USING THE CONFOCAL LASER-SCANNING MICROSCOPE

A new method has been developed for quantifying drug release processes within controlled release dosage forms using the confocal laser scann ing microscope (CLSM). The changing internal distribution of a fluores cent marker drug (minocycline HCl) within a spherical controlled relea se pellet undergoing drug release was followed using CLSM, which allow ed internal mapping of the drug non-invasively and without prior sampl e preparation. Image analysis routines were developed to quantify the changing drug concentration profile with time across the radius of the pellet, and the results were fitted to a theoretically derived mathem atical model which predicted a biphasic depletion mechanism. The exper imental results closely fitted the predicted profile, and enabled calc ulation of the drug dissolution rate constant, the diffusion coefficie nt of drug within the matrix, and the time drug dissolution within the matrix ended.