COMPARISON OF THE EFFECTS AND DISPOSITION KINETICS OF LIDOCAINE AND (+ -)PRILOCAINE IN PATIENTS UNDERGOING AXILLARY BRACHIAL-PLEXUS BLOCK DURING DAY-CASE SURGERY/

Objective: The aim of this investigation was to compare the clinical e ffects and pharmacokinetics of lidocaine and prilocaine in two groups of 15 patients undergoing axillary brachial plexus anaesthesia. Method s: The study had a randomised design. Patients were allocated to one o f the two groups of 15. Each group received either lidocaine (600mg = 2.56 mmol/L + 5 mg/L adrenaline) or prilocaine (600mg = 2.72 mmol/L 5 mg/L adrenaline), injected over a period of 30 seconds. Onset of the surgical analgesia was defined as the period from the end of the inje ction of the local anaesthetic to the loss of pinprick sensation in th e distribution of all three nerves. Results: The mean onset time of su rgical analgesia of both lidocaine and prilocaine was 10 minutes. Lido caine was biexponentially eliminated with a rapid elimination phase ha lf-life (t1/2 alpha) of 9.95 +/- 14.3 minutes and a terminal eliminati on phase half-life (t1/2 beta) of 2.86 +/- 1.55 hours. Lidocaine was m etabolised to MEGX (monoethylglycylxylidide); time to reach maximum pl asma concentration (t(max)) 2.3 +/- 0.8 hours; maximum plasma concentr ation (C-max) 0.32 +/- 0.13 mg/L; t1/2 beta 2.4 +/- 2.4 hours. Lidocai ne total body clearance was 67.8 +/- 28.8 L/h. Prilocaine was rapidly and biexponentially eliminated with a t1/2 alpha of 9.4 +/- 18.4 minut es and a t1/2 beta of 2.12 +/- 1.28 hours. The total body clearance of prilocaine (150 +/- 53 L/h) was higher than that of lidocaine (p = 0. 0255). Both compounds demonstrated a comparable volume of distribution (Vd), while the volume of distribution at steady-state (V-ss) and the volume of distribution in the second compartment (V-beta) values of p rilocaine were a factor of 1.6 higher than those of lidocaine (p < 0.0 01). Both compounds showed a comparable t1/2 alpha (p > 0.8) and a com parable t1/2 beta (p = 0.26). Conclusion: Following axillary administr ation, lidocaine and prilocaine demonstrated similar pharmacokinetic b ehaviour and could therefore be used as the clinical preference for th is regional anaesthesia technique.