Comparison of the disposition kinetics of lidocaine and ± prilocaine in 20 patients undergoing intravenous regional anaesthesia during day case surgery

Objective: The aim of this investigation was to compare the pharmacokinetics of lidocaine and prilocaine in two groups of 10 patients undergoing intravenous regional anaesthesia. Method: The study had a randomized design. The patients were allocated to one of the two groups of 10. Each group received either lidocaine (200 mg= 0.855 mw) or prilocaine (Citanestr̀, 200 mg = 0.909 mM), injected intravenously over a period 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: The 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 bi-exponentially eliminated with a t1/2a of 4.3 ± 2.1 min and a t1/2β of 79.1 ± 31.2 min. Total body clearance was 0.86 ± 0.39 litres/min. Prilocaine is rapidly and bi-exponentially eliminated with a t1/2aof 3.0 ± 1.6 min and a t1/2β 29.9 ± 15.7 min. The total body clearance of prilocaine 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 (Vd′ Vss and Vβ) and a comparable t1/2a (4.3 ± 2.1 vs. 3.0 ± 1.6 min; P=0.1780). The t1/2β for the two compounds were different (P=0031); 7.-1 31.2 min for lidocaine and 29.9 ± 15.7 min for prilocaine. The mean residence time (MRT) of lidocaine (193 ± 233 min) also differed significantly from that of prilocaine (33.4 ± 19.9 min; P=0.0022). Conclusion: Lidocaine is preferred for relatively long procedures and prilocaine for short procedures.