RESUMO
The effects of phenytoin on the neuromuscular blockades(NMBs) appear to be different according to the time intervals between their administration. In general, single injection of phenytoin immediately prior to NMB may produce the augmentation of NMBs, while long-term phenytoin therapy on the neuromuscular blocking actions of vecuronium were investigated in rats using the sciatic nerve-anterior tibialis muscle preparation. Eighteen male rats were divided randomly into three groups; Group I(without phenytoin), II (single phenytoin 40 mg/kg I.V. just prior to vecuronium administration), III(phenytoin 40 mg/ kg administered intraperitoneally twice daily for 14 days). In all the groups, vecuronium with the cumulative dose-response technique of ED was administered intravenously. The results are as follows; 1) The ED of vecuronium was significantly higher in Group III(162.3+/-12.4 ug/kg) than in Group I or II(135.7+/-11.0 or 126.77 +/-16.66 u/kg, respectively), and also the ED did so(218.1 +/-28.3 or respectively). 2) In the cumulative dose-response curves with vecuronium, the slope of Group III was significantly lower than that of Group I or IL 3) The plasma concentrations of phenytoin in Group II and III were 60.9+/-15.1 ug/ml and 9.0+/-2.3 ug/ml, respectively. 4) The duration of vecuronium was significantly shorter in Group III(22.3+/-5.2 sec) than in Group I or II(34.7+/-5.7, 44.3+/-8.7 sec, respectively), and also the recovery index did so(36.8+/-4.4, 43.8+/-5.6 and 27.7+/-5.7 sec in Group I, II and III, respectively). 5) There was no statistically significant difference of mean arterial pressure, heart rate, body temperature, acid-base status and electrolytes among groups. In conclusion, pheytoin with long-term therapy may induce the resistance to vecuronium and shorten its recovery. However, there is no effect in the single injection of phenytoin on the vecuronium-induced neuromuscular block.