Similar Motor Block Effects and Disposition Kinetics between Lidocaine and (±)Mepivacaine in Patients Undergoing Axillary Brachial Plexus Block during Day Case Surgery

The aim of this investigation was to compare the clinical effects and pharmacokinetics of lidocaine (one metabolite) and mepivacaine (two metabolites) in 2 groups of 15 patients undergoing axillary brachial plexus anaesthesia. The study had a randomised design. The 30 patients were divided into 2 groups. The patients received either lidocaine (600 mg = 2.561 mMol + 5 μg ml(-1) adrenaline) or mepivacaine (600 mg = 2.436 mMol + 5 μg ml(-1) adrenaline), injected via the axilla near the brachial plexus over a period of 30 s. Onset of surgical analgesia was defined as the period from the end of the local anaesthetic injection to the loss of pinprick sensation in the distribution of the ulnar, radial, and median nerve. Motor block was measured. Onset of motor block was similar for both drugs. Lidocaine is eliminated biexponentially with a t(1/2α) of 9.95 ± 14.3 min and a t(1/2β) of 2.86 α 1.55 h. Lidocaine is metabolised into MEGX (t(max) 2.31 α 0.84 h; Cmax 0.32 α 0.13 mg l(-1); t(1/2β) 2.36 α 2.35 h; total body clearance was 67.9 α 28.9 l h(-1)). Mepivacaine is eliminated rapidly and monoexponentially with a t(1/2) of 4.78 α 2.38 h, a C(max) of 3.89 α 0.83 mg l(-1), and a t(max) of 0.41 α 0.19 h. The total body clearance of mepivacaine is 50% of that of lidocaine, 26.9 α 10.6 l h(-1) vs. 67.9 α 28.9 l h(-1), respectively (p <0.0001). (α)Mepivacaine is metabolised into (α)4-OHmepivacaine (C(max) 0.45 α 0.25 mg l(-1); t(1/2β) 6.48 α 6.57 h) and (α)2,6-pipecoloxylidide (C(max) 0.56 α 0.30 mg l(-1); t(1/2b) 1.48 α 0.74 h). For the axillary brachial plexus block, lidocaine and mepivacaine show similar pharmacodynamic and pharmacokinetic behaviour, despite the number of metabolites, and can therefore be used to the clinical preference for this regional anaesthetic technique.