The arterial and venous difference of thiopental pharmacokinetics and its impact on the onset of pharmacologic effect were examined in 6 male surgical patients with normal renal and hepatic functions during short time period of 6hrs post-intravenous bolus injection over 5 second (5㎎/㎏). Arterial and venous blood samples were withdrawn from radial arteries and cephalic or basilica veins, respectively at the time of right before and after injection(0), 5, 10, 20, 30, 45(sec), 1, 2, 5, 10, 30(min), 1, 2, 3, 4, 5, 6(hrs). Serum concentrations of thiopental were determined by reverse phase, high performance liquid chromatography and the clinical endpoints of anesthesia induction were interpreted as the time of loss of consciousness by observing spontaneous closing of eyes and loss of eyelash reflex.
As the results, significant differences between arterial and venous concentrations were noted during early phase lasting up to 10minutes. Arterial data was best fitted to tri exponential decay model and venous data to bi-exponential decay model. In analyzing pharmacokinetic parameters with serum data of 6 hrs duration, there were no significant differences in AUCo-∞, AUCo-t, and clearance(p>0.05), but significant differences in peak concentrations(arterial : 103.97±12.15, venous : 17.487±5.206㎍/㎖), and times to peak(arterial : 0.167±0.037, venous : 1.653±0.712min), AUMCo-t, MRT, apparent terminal half-life and apparent steady-state volume of distribution. Spontaneous eye closures were observed within 20 seconds(range : 10~20sec) after the end of injection where arterial concentrations were at peak(n=3) or right after peak(n-3) and otherwise, venous concentrations were at low or even almost at zero(n=3) and otherwise, venous concentrations were at low or even almost at zero(n=3), reflection the fact that arterial concentrations are directly correlated to the clinical efficacy and more important in pharmacokinetic and dynamic aspect of drug.
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