COMPARISON OF THE DISPOSITION KINETICS OF LIDOCAINE AND (+ -)PRILOCAINE IN 20 PATIENTS UNDERGOING INTRAVENOUS REGIONAL ANESTHESIA DURING DAY-CASE SURGERY/

Objective: The aim of this investigation was to compare the pharmacoki netics of lidocaine and prilocaine in two groups of 10 patients underg oing intravenous regional anaesthesia. Method: The study had a randomi zed design. The patients were allocated to one of the two groups of 10 . Each group received either lidocaine (200mg = 0.855 mM) or prilocain e (Citanest(R), 200 mg = 0.909 mM), injected intravenously over a peri od of 30 s. Onset of the surgical analgesia was defined as the period from the end of the injection of the local anaesthetic to the loss of pinprick sensation in the distribution of all three nerves. Results: T he mean onset time of surgical analgesia of lidocaine was 11.2 +/- 5.1 min and that of prilocaine was 10.9 +/- 6.0 min. After releasing the tourniquet, lidocaine is hi-exponentially eliminated with a t(1/2 alph a) of 4.3 +/- 2.1 min and a t(1/2 beta) of 79.1 +/- 31.2 min. Total bo dy clearance was 0.86 +/- 0.39 litres/min. Prilocaine is rapidly and b i-exponentially eliminated with a t(1/2 alpha)of 3.0 +/- 1.6 min and a t(1/2 beta) of 29.9 +/- 15.7 min. The total body clearance of priloca ine is higher than that of lidocaine, 4.15 +/- 1.31 vs. 0.86 +/- 0.39 litres/min, respectively (P = 0.0007). Both compounds show comparable volumes of distribution (V-d, V-ss and V-beta) and a comparable t(1/2 alpha) (4.3 +/- 2.1 vs. 3.0 +/- 1.6 min; P = 0.1780). The t(1/2 beta) for the two compounds were different (P = 0031); 79.1 +/- 31.2 min for lidocaine and 29.9 +/- 15.7 min for prilocaine. The mean residence ti me (MRT) of lidocaine (193 +/- 233 min) also differed significantly fr om that of prilocaine (33.4 +/- 19.9 min; P = 0.0022). Conclusion: Lid ocaine is preferred for relatively long procedures and prilocaine for short procedures.