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 effects and pharmacokinetics of lidocaine and prilocaine in two groups of 15 patients undergoing axillary brachial plexus anaesthesia.

Methods: The study had a randomised design. Patients were allocated to one of 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 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 both lidocaine and prilocaine was 10 minutes. Lidocaine was biexponentially eliminated with a rapid elimination phase half-life (t((1/2)alpha)) of 9.95 +/- 14.3 minutes and a terminal elimination phase half-life (t((1/2)beta)) of 2.86 +/- 1.55 hours. Lidocaine was metabolised to MEGX (monoethylglycylxylidide); time to reach maximum plasma concentration (tmax) 2.3 +/- 0.8 hours; maximum plasma concentration (C(max)) 0.32 +/- 0.13 mg/L; t((1/2)beta) 2.4 +/- 2.4 hours. Lidocaine total body clearance was 67.8 +/- 28.8 L/h. Prilocaine was rapidly and biexponentially eliminated with a t((1/2)alpha) of 9.4 +/- 18.4 minutes and a t((1/2)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 prilocaine were a factor of 1.6 higher than those of lidocaine (p < 0.001). Both compounds showed a comparable t((1/2)alpha) (p > 0.8) and a comparable t((1/2)beta) (p = 0.26).

Conclusion: Following axillary administration, lidocaine and prilocaine demonstrated similar pharmacokinetic behaviour and could therefore be used as the clinical preference for this regional anaesthesia technique.