Revista de Bioanálise e Biomedicina

31 P-NMR and Differential Scanning Calorimetry Studies for Determining Vesicle’s Drug Physical State and Fraction in Alendronate Liposomes

Abstract

Eyal Afergan, Yousef Najajreh, Dikla Gutman, Hila Epstein, Omar Elmalak and Gershon Golomb

Background: A liposomal delivery system requires a complete understanding of the physicochemical characteristics of the drug– liposome system in order to predict their behavior and stability in-vitro and in-vivo .

Objectives: Develop a rapid and simple experimental method to determine the fractions of the drug, alendronate (ALN), encapsulated and as a free form distributed in the liposomal suspension, and the physical state of the encapsulated drug.

Methods: 31 P-NMR measurements utilizing Ga +3 as a shifting reagent in comparison to HPLC determinations, theoretical calculations and differential scanning calorimetry (DSC) studies of various liposomal ALN formulations.

Results: The 31 P-NMR demonstrated that titrating liposomal ALN with increasing amounts of Ga +3 induced a signi fi cant shift in the exterior fraction without changing the interior fraction. Quantitative determination of the encapsulated and non-encapsulated f ractions of ALN has been achieved at Ga +3 concentrations of 3.2-25mM. The DSC study revealed that none of the formulation ingredients is in a solid phase.

Conclusions: 31 P-NMR was found to be sensitive enough to allow accurate differentiation of the distributed fractions of ALN, encapsulated and the non-encapsulated free form. Based on theoretical calculations and DSC analysis it can be concluded that AL N is dissolved in the aqueous core of the liposome.