Effect of amitriptyline and dexmedetomidine combination on block duration in rat sciatic nerve blockade

Objective: Local anesthetic effects of amitriptyline are more potent than bupivacaine in high concentration and severity of neurotoxic effects increase depending on dose. Neurotoxic effects limits usage of amitriptyline as a local anesthetic. In this study, we aimed to compare the effect of different amitriptyline dose in combination with dexmedetomidine on block duration in rat sciatic nerve with amitriptiyline alone and bupivacaine.Materials and Methods: Total 42 Sprague-Dawley male rats were included into study. There were six groups and each groups contained seven rats. Groups 1: amitriptyline 0.625 mg, Groups 2: amitriptyline 0.312 mg, Groups 3: dexmedetomidine 10 µg, Groups 4: amitriptyline 0.625mg and dexmedetomidine 10 µg, Groups 5: amitriptyline 0.312 mg and dexmedetomidine 10 µg, Groups 6: 0.5% bupivacaine.Rats were anesthetized with 5mg/kg intraperitoneal ketamine injection. The sciatic nerves were exposed by lateral incision of the right thighs on posterior approach. 0.2 mL test dose of local anesthetic was injected beneath the fascia surrounding the nevre but out side of epineurium and perineurium. Effectiveness of local anesthetic were determined by nociceptive, proprioceptive response and motor function. Kruskal-Wallis test was used to analyze the data within the groups. One-way analysis of variance (Oneway ANOVA) and Post Hoc Tukey HSD test were used to determine statistical significance of difference between the groups. Data are presented as mean ± standart deviation. p<0.05 was considered to be statistically significant.Results: There was no nociceptive, proprioceptive block in opposite limb after sciatic nevre local anesthetic injection in rats. Full recovery was found after block in all rats without any clinical neurologic deficit.In our study, amitriptyline, and amitriptyline and dexmedetomidine combination was showed more long acting local anesthetic effect than bupivacaine. Altough it was not statistically significant, mean time to block were shorter in bupivacaine group than amitriptyline group. 0.625 mg amitriptyline and 10 µg dexmedetomidine combination extremly prolonged recovery times of block, compared with 0.625 mg amitriptyline alone. 0.312 mg amitriptyline and 10 µg dexmedetomidine combination slightly prolonged recovery times of block which was not statistically significant. Mean time to block significantly delayed in combination groups.Conclusion: In this study it was shown that amitriptyline and dexmedetomidine combination prolongs duration of block and increasing dose of amitriptyline can cause to more additive effect. It was found that dexmedetomidine addition delayed mean time to block.Key words: Sciatic nerve blockade, Amitriptyline, Dexmedetomidine, Long acting local anesthetic