Effects Of Phenobarbital And Intravenous Anesthetics On The Pparmacokinetics Of Lidocaine During Anesthesia

Objective: Lidocaine is a kind of local anesthetic used widely in clinic with quick, strong and lasting action . Combined spinal epidural anesthesia(CSE) is a anesthetic method which has many advantages of low dosage and low damage . Phenobarbital is the inducer to hepatomicrosome and drug metabolism enzyme. It has not been reported whether phenobarbital affected the pharmacokinetics of lidocaine during anesthesia. The study elucidated the regular pattern of lidocaine in absorption, distribution and elimination after it entered epidural cava when CSE was performed. The study investigated the influences of phenobarbital and intravenous anesthetics on the pharmacokinetics of lidocaine in order to provide data for clinic, which applied safely sedative and narcotic before operation. Methods: ① Sixteen patients who were performed CSE at abdomen and low limb were included in this study. The patients were divided randomly into two groups. One group received phenobarbital and the other did not before operation. After injecting lidocaine radial artery blood was collected at 5,10,15,20,40,60,90,120,150 and 180min. ② Twelve adult patients scheduled for elective major abdominal and orthopedic surgical procedures were included in this study. they were randomly allocated into two groups. A combination of intravenous anesthesia (TIVA) and epidural anesthesia was applied to group Ⅰ and epidural block was applied to group Ⅱ.The blood samples were collected after anesthesia in the sequence of5,10,15,30,60,90,120,150,180,360,480 min. lidocaine concentration in serum was determined with fluorescence polarization immunoassay (FPIA). Data were handled with the program 3P97. The effects of Phenobarbital and intravenous anesthetics on the pharmacokinetics of lidocaine were investigated. Result :① No matter whether phenobarbital was used or not before operation during CES,two-compartment model with first order absorption was appeared in lidocaine which was given by extra vascular. Weight was 1. Main pharmacokinetics parameters of lidocaine were respectively:Tmax : 7.567±1.230)and 8.077±1.631min(P>0.05), Cmax : 2.156±0.182 and 2.099±0.188 mg.L-1(P>0.05), β: 0.007±0.001 and(0.006±0.003 min-1(P>0.05) , T1/2β: 109.1±20.78 and 133.3±59.61 min(P>0.05). ② The pharmacokinetic parameters of lidocaine in the two groups after epidural administration of lidocaine are as follows: Tmax: 8.4±0.6 and 9.0±0.6 min(P>0.05), Cmax : 2.16±0.25 and 2.02±0.2 mg.L-1(P>0.05), T1/2β: 3.34±1.67 and 2.15±0.63 h-1(P>0.05) respectively.Conclusion:This study showed: ① effect of phenobarbital on the pharmacokinetics parameters of lidocaine during epidural anesthesia was not significant (P>0.05).So the effect of phenobarbital on dosage of lidocaine must not be considered during CSE. ② intravenous anesthetics has no significant effects on the pharmacokinetics of lidocaine during epidural block.