A Comparative Study on Physicochemical and Analytical Characterizations of Doxil® and its Generic Drug Products

Doxil®, a PEGylated liposomal doxorubicin (DOX) hydrochloride suspension, was the first liposome drug product approved by the U.S. Food and Drug Administration (FDA). Although off-patent, limited generic products have been approved due to challenges in achieving bioequivalence compounded by manufacturing complexity. Regulatory agencies require generic drug products to be bioequivalent to the reference listed drug. In this regard, we developed various analytical methods to analyze Doxil® and its generic drug products for multiple attributes, including liposome size distribution, zeta potential, DOX content, lipid content, purity, non-encapsulated doxorubicin, morphology, nanostructure similarity, and quantified in vitro release. Batch-to-batch variation exists across attributes for different formulations. Minor differences in particle size and zeta potential were observed. Cryo-TEM imaging reveals the distinct coffee bean shape and morphology of the Doxil® liposome. SAXS similarity analysis shows a distinct difference in nanostructure for Dr. Reddy's formulation compared to the innovator formulation. Still, it is revealed to be a consequence of liposome uniformity and homogeneity as depicted in cryo-TEM images. Several methods developed in this work can be complementary to provide a more thorough physicochemical analysis for generic evaluation. Size, morphology, and nanostructure evaluated by DLS, cryo-TEM, and SAXS should be readily employed to assess physicochemical similarity. Content, impurity identification, and amount of free non-encapsulated DOX are used to evaluate formulation sameness. The methods developed in this work provide a physicochemical framework for analytical comparison of complex liposomal generics and may support subsequent development efforts to improve generic drug availability for patient populations in need.