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

Abstract

To evaluate whether a ternary system composed of hydroxypropyl-β-cyclodextrin (HP-βCD) further encapsulated into egg phosphatidylcholine liposomes (LUV) could prolong the action and reduce the toxicity of ropivacaine (RVC). Dynamic light scattering and NMR were used to characterize the inclusion complex (RVC:HP-βCD), liposomal (RVC:LUV) and ternary (LUV:RVC:HP-βCD) 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. 1:1 RVC:HP-βCD inclusion complex was encapsulated in liposomes (220.2±20.3nm size, polydispersity <0.25, zeta potentials=-31.7±1.4mV). NMR (diffusion-ordered spectroscopy (DOSY)) revealed stronger anaesthetic binding to LUV:RVC:HP-βCD (Ka =342m-1 ) than to RVC:HP-βCD (Ka =128m-1 ) or liposomal formulation (Ka =22m-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-βCD≥RVC:HP-βCD>RVC:LUV. Accordingly, in-vivo sensory block of free RVC (180min) was prolonged ca. 1.7 times with the ternary system and RVC:HP-βCD (300min) and 1.3 times with RVC:LUV (240min). 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.