Novel dissolution methods for drug release testing of Long-Acting injectables

Long-acting parenteral drug products are a popular choice for therapeutic areas requiring long term treatment. These products range from dispersed systems such as drug suspensions and polymeric microspheres to in situ forming polymeric implants. The lack of reliable drug release testing methods for these drug products not only impedes the development of new drug products but also affects generic drug development. Current release methods suffer from a range of problems such as high variability, poor reproducibility, poor discriminatory ability, lack of depot-like structure formation (that could mimic the in vivo situation). Moreover, shorter duration (less than a week) of release renders them unsuitable for in vitro-in vivo correlations (IVIVCs). To overcome these issues, novel adapters were developed for both USP-type-II & IV apparatus. These adapters were validated and assessed using the long-acting injectable (LAI) suspension drug product Depo Provera 150® as well as its Q1/Q2 equivalents. For USP-type-IV apparatus, two open adapter designs (conical and ellipsoidal shaped cavity with volume capacities of 50 µl and 1 ml, respectively) were developed. A closed conical adapter design with a volume capacity of 0.05 ml was developed for USP apparatus type-II. All three novel adapter designs effectively retained the suspensions, achieved release durations of 3-6 weeks with good reproducibility, minimal variability (RSD≤5%) and had good discriminatory ability. Based on this, the adapter-based dissolution methods were deemed suitable for IVIVC development of long-acting injectables. A successful Level A IVIVC was developed for Depo SubQ Provera 104® and its Q1Q2 equivalents using USP apparatus type IV with a conical adapter design. The closed adapter design for apparatus type-II was also investigated for suitability with risperidone in situ forming implants. The adapter was able to securely retain and maintain the shape of the in situ forming implants and resulted in release profiles of up to one month with good discriminatory ability and low standard error (RSD≤5%). These novel adapters hold promise of wide use for in vitro release testing of different long-acting parenteral drug products.