Preparation Of Liposomal Lidocaine Solution And Anesthetic Effects Of Its Injection Intrathecally In Rats

Objective To explore the process of the preparation of 2% liposomal lidocaine solution and evaluate its physicochemical characterization. To investigate the anesthetic effects of intrathecal 2% liposomal lidocaine solution in rats.Methods Egg yolk phosphatidylcholine, cholesterol, diethylethyl, pure lidocaine powder and pH=6.0 phosphate buffer were used to prepare 2% liposomal lidocaine solution under reverse-phase evaporation vesicle method. The morphology of 2% liposomal lidocaine was observed , its sizes were calculated by microscopy and its encapsulation efficiency was measured under high performance liquid chromatography. The empty liposomes were also prepared by using the same method. 2% lidocaine phosphate solution were prepared. Fifty healthy female SD rats weighing 240~310g were randomly divided into five groups with ten animals in each group: free lidocaine group (F), liposomal lidocaine group(L), normal saline group(N), phosphate buffer group(P)and empty liposomes group(E). Group F received intrathecally 2% free lidocaine solution 0.8mg at the speed of 0.02 mg·s-1 while group L were injected 2% liposomal lidocaine solution instead. Group N, Group P and Group E were injected the same volume of normal saline, phosphate buffer and empty liposomes at the same speed separately. The acting time, motor recovery time and sensory recovery time were observed in the hind limbs of the rats by the behavior observation and dynamic plantar anesthesiometer; the time of motor blockade was assessed using revised Bromage scale.Results The morphology of 2% liposomal lidocaine was like the cell, its sizes were 150 -2000nm, its encapsulation efficiency was about 37.3 % . Group N, Group P and Group E showed no anesthetic effect after intrathecal injection. There was no significant difference in the acting time between Group F and Group L P>0.05). The motor and sensory recovery times in group L , however, were significantly longer than those of group F(P<0.01). Motor blockade time of three grades also showed significant differences between group F and group L(P<0.01).Conclusions It can be used egg yolk phosphatidylcholine , cholesterol, diethylethyl, lidocaine powder and PH=6.0 phosphate buffer to prepare 2% liposomal lidocaine solution under reverse-phase evaporation vesicle method; The effects of spinal anesthesia in rats can be prolonged by liposomal lidocaine. This indicates the prolongation is caused by a slow release of drugs from liposomes.