Anaesthetic benefits of a ternary drug delivery system (Ropivacaine-in-Cyclodextrin-in-Liposomes): in-vitro and in-vivo evaluation

Objectives To evaluate whether a ternary system composed of hydroxypropyl-beta-cyclodextrin (HP-beta CD) further encapsulated into egg phosphatidylcholine liposomes (LUV) could prolong the action and reduce the toxicity of ropivacaine (RVC). Methods Dynamic light scattering and NMR were used to characterize the inclusion complex (RVC : HP-beta CD), liposomal (RVC : LUV) and ternary (LUV : RVC : HP-beta CD) systems containing 0.25% RVC. Their encapsulation efficiency, release kinetics, in-vitro cytotoxicity and in-vivo anaesthetic effect (paw-withdraw tests in mice) were also evaluated. Key findings 1 : 1 RVC : HP-beta CD inclusion complex was encapsulated in liposomes (220.2 +/- 20.3 nm size, polydispersity <0.25, zeta potentials = -31.7 +/- 1.4 mV). NMR (diffusion-ordered spectroscopy (DOSY)) revealed stronger anaesthetic binding to LUV : RVC : HP-beta CD (K-a = 342 m(-1)) than to RVC : HP-beta CD (K-a = 128 m(-1)) or liposomal formulation (K-a = 22 m(-1)). The formulations promoted in-vitro sustained drug release and partially reverted the cytotoxicity of RVC against 3T3 fibroblasts in the profile: LUV : RVC : HP-beta CD >= RVC : HP-beta CD > RVC : LUV. Accordingly, in-vivo sensory block of free RVC (180 min) was prolonged ca. 1.7 times with the ternary system and RVC : HP-beta CD (300 min) and 1.3 times with RVC : LUV (240 min). Conclusions These results confirm the suitability of this double-carrier system in clinical practice, to decrease the toxicity and prolong the anaesthesia time evoked by RVC.