Use of in vitro release models in the design of sustained and localized drug delivery systems for subcutaneous and intra-articular administration

Predictive in vitro release methods for parenteral depots should be developed with emphasis on the intended administration site as well as the formulation principles and the properties of drug administered. For subcutaneous/intra-articular administration, drug release from the depot and subsequent tissue transport away from the injection site involve diffusive and/or convective processes. The present review gives an account of drug transport in the synovial joint and the subcutaneous (or connective) tissue and how to implement such drug transport processes in the release model, e.g. the use of dialysis membrane for simulating the synovium and hydrogels for mimicking the subcutaneous tissue. This review summarizes the in vitro release studies performed using the rotating dialysis cell model including drug release assessment for the design of lipophilic drug/prodrug solutions. The initial exploration of the UV imaging technology for studying drug transport and release processes for depots intended for subcutaneous injection is commented on.