The significance of drug-to-lipid ratio to the development of optimized liposomal formulation.

Liposomes are considered to be one of the most extensively investigated drug delivery nanosystems. Each drug can be loaded either in the liposomal hydrophilic core or within the lipidic bilayer and delivered eventually to the proper site into the organism. There are already many marketed approved liposomal products. The development of a liposomal product is a quite complicated process, while many critical parameters have to be investigated during the preparation process. The present study deals with the drug-to-lipid ratio (D/L ratio), which is a critical process parameter, expresses the actual capacity of the liposome to accommodate the drug and can play a key role at the optimization of every liposomal formulation. D/L ratio is affected by the composition, the different biomaterials and the loading method being used, so the improvement of D/L ratio can optimize the liposomal formulation. D/L ratio can be used as an index of the effectiveness of the preparation method too. Furthermore, D/L ratio influences the therapeutic efficacy of the liposomal product, expressing the actual dose of the drug being administrated. There is a variety of analytical methods, quantifying the drug and the lipids and estimating eventually the D/L ratio. According to the regulatory framework of nanomedicine, about the development of nanosimilars, D/L ratio is a necessary element for the nanosimilar product description and the statement of product comparability.