---

Abstract Background & aim: The methods to increase duration of spinal anesthesia is always noticed.,the aim of this study was to investigate the effect of mexiletine on duration of sensory and motor block in spinal anesthesia. Methods: In a clinical trial study 60 patients with age 18-50, ASA 1,2 who were scheduled for lower limb elective surgery at Shahid Bahonar hospital were enrolled. They were randomally assigned in two groups of control and intervention. Intervention group received oral mexiletine 200 mg 2hours before operation and control group received placebo.Spinal anesthesia was carried out with lidocaine /5 (100mg) in L2-L3 or L3-L4 space by the same method in two groups. Pulse rate,Pulse oximetry and mean arterial blood pressure were recorded in two groups every 5-10 minutes.Also the duration of sensory and motor block was recorded. The results were analyzed with Student t-test,Chi square and Mann-Whitney. Results:The onset of sensory and motor block was significantly faster in intervention group.(P<0/01) The duration of sensory and motor block was significantly more in intervention group than control.(P<0/001) The pulse rate in intervention group were signifigantly less than control group in 0,5,10,60,75 minutes after spinal injection. (P<0/05) Conclusion: Mexiletine is effective in increasing duration of sensory and motor block in spinal anesthesia with lidocaine and also increases the onset of both sensory and motor block with lidocaine. Key Words: Mexiletine, Sensory and motor block, Spinal anesthesia, Lidocaine