Effect of Fentanyl on Lidocaine-Induced Convulsions in Mice

This study was undertaken to examine the effect of fentanyl on lidocaine-induced convulsions in mice. Seventy-five male mice were used and divided into five groups, 15 in each. Convulsions were obtained by lidocaine injection subcutaneously (150 mg/kg), in a dose volume of 0.1 ml/10 g body weight over the upper back. The five groups were: (a) <i>control group:</i> pretreated with normal saline; (b) <i>F50 group:</i> pretreated with fentanyl 50 µg/kg; (c) <i>F100 group:</i> pretreated with fentanyl 100 µg/kg; (d) <i>F200 group:</i> pretreated with fentanyl 200 µg/kg, and (e) <i>F100+N group:</i> pretreated with fentanyl 100 µg/kg plus naloxone 1 mg/kg. The pretreatments were given intraperitoneally (i.p.) 5 min prior to lidocaine injection. After lidocaine injection, the latency to the onset of generalized convulsions was observed for 12 min and recorded. The severity of convulsions was assessed and scored as 1 = mild, 2 = moderate, and 3 = severe. The recovery or death of the mice were also recorded. Student’s t, Mann-Whitney U, and Fisher’s exact tests were used to analyze the data. Compared with the control group (431.7 ± 37.3 s), the latencies of onset of convulsions in the fentanyl groups were dose-dependently decreased (F50: 331.0 ± 37.1 s; F100: 240.3 ± 28.6 s, p < 0.001; F200: 188.7 ± 19.4 s, p < 0.001), and the decreased latency was reversed by naloxone (F100+N: 412.9 ± 34.1 s). Compared with the control group (1.13 ± 0.19), the severities of convulsions in the fentanyl groups were also increased in a dose-dependent manner (F50: 1.47 ± 0.19; F100: 1.93 ± 0.21, p < 0.05; F200: 2.46 ± 0.17, p < 0.001). Similarly, the increased severity was reversed by naloxone (F100+N: 1.33 ± 0.16). There was no death in the control and naloxone-treated groups. The incidences of death were 2/15 in F50 group, 5/15 in F100 group, and 7/15 in the F200 group (p < 0.05). The results of this study demonstrated that fentanyl potentiates the lidocaine-induced convulsions in a dose-dependent manner in mice, and this effect may be mediated by an opioid mechanism.