Osmolality of Excipients for Parenteral Formulation Measured by Freezing Point Depression and Vapor Pressure - A Comparative Analysis.

Purpose: To investigate the difference in methods to determine the osmolality in solutions of stabilizers used for long-acting injectable suspensions.

Methods: The osmolality was measured by freezing point depression and vapor pressure for 11 different polymers and surfactants (PEG 3350, 4000, 6000, 8000, 20,000, PVP K12, K17 and K30, poloxamer 188, 388 and 407, HPMC E5, Na-CMC, polysorbate 20 and 80, vitamin E-TPGS, phospholipid, DOSS and SDS) in different concentrations.

Results: Independently of the measuring method, an increase in osmolality with increasing concentration was observed for all polymers and surfactants, as would be expected due to the physicochemical origin of the osmolality.