Influence of Testing Parameters on In Vitro Tramadol Release from Poloxamer Thermogels using the Immersion Cell Method

The immersion cell is an in vitro performance test of drug release from semisolids. Several studies made use of immersion cells to investigate drug release from thermosensitive Poloxamer-based gels; however, specifications on the parameter setting are not yet available. Therefore, the aim of this study was to evaluate the influence of testing parameters on tramadol (a model drug) release, release rate, and dissolution efficiency (DE) from Poloxamer gels, using immersion cells. The thermosensitive gelling formulation showed batch-to-batch uniformity of gelling behavior, drug content, and drug release. The use of a membrane in the immersion cell resulted in slower drug release as compared to the absence of a membrane. Moreover, the faster the paddle rotation, the faster the drug release was. Membrane thickness showed a strong and significant linear relationship with corresponding DE values (Pearson's correlation coefficient, r = -0.9470; p = 0.004). Factors that did not influence drug release include paddle position, i.e., distance between paddle and membrane, as well as membrane mean pore size. This study sets forth the importance of carefully controlling the following parameters including presence/absence of membrane, paddle rotation speed, and membrane thickness during the setup of release experiments from gels using immersion cells.