RESUMO
Objective:To develop a novel sustained-release local anesthetic microspheres and evaluate the effects on sciatic nerve block in rabbits.Methods:The magnetic lidocaine microspheres were prepared by W 1/O/W 2 compound emulsion method, investigating their external morphology, measuring the magnetic response characteristics by the VSM and draw the hysteresis loop.The encapsulation efficiency and drug-loading rate were calculated, and the cumulative release curves in vitro were drawn.Fifteen healthy rabbits (half male and half female), aged 5-6 months, weighing 3.0-3.5 kg, were selected for sciatic nerve block and divided into 3 groups ( n=5 each) using a random number table method: magnetic response lidocaine microspheres group (PL group), normal saline control group (C group) and lidocaine group (L group). Magnetic response lidocaine microsphere buffer 2 ml, normal saline 2 ml and 2% lidocaine 2 ml were injected around the rabbit sciatic nerve through a catheter in PL, C and L groups, respectively.The applied magnetic field was withdrawn at 60 h after injection.Before injection (T 0) and at 30 min and 2 , 8, 16, 24, 48, 60, 62 and 64 h after injection (T 1-9), the compound action potentials and conduction velocities of bilateral sciatic nerve trunks were measured, and block was assessed using toe reflex score and modified Tarlov score. Results:The magnetic lidocaine microspheres were brown in color and observed as monodisperse, regular spheres with a diameter of (9±3) μm, an encapsulation rate of 46.18%, a drug loading of 6.02%, and a superparamagnetic release rate of 97% in vitro at 60 h. The hysteresis loop passed through the origin and no hysteresis occurred with the absence of an external magnetic field.Compared with C group, the action potentials and conduction velocities of the sciatic nerve, toe reflex score and modified Tarlov score were significantly decreased at T 1-T 8 in PL group ( P<0.05). Compared with L group, the action potentials and conduction velocities of the sciatic nerve were significantly increased at T 1, the action potential was decreased at T 2-T 8, the conduction velocity was decreased at T 3-T 8, the toe reflex score was increased at T 1 and decreased at T 3-T 8, and the modified Tarlov score was increased at T 1 and T 2 and decreased at T 3-T 8 in PL group ( P<0.05). Conclusions:Magnetic response lidocaine microsphere is successfully developed with good magnetic responsiveness and release and can prolong the sciatic nerve block time in rabbits.