EditorThe British Journal of Anaesthesia has published six papers comparing the effects of levobupivacaine, the S()-stereoisomer of bupivacaine with bupivacaine and ropivacaine, between 1998 and 2004,16 and three papers79 on various aspects of levobupivacaine alone. None of these papers calculated the concentration according to molarity. Two of them noted that there is a difference between the clinical and molar concentrations of levobupivacaine that needs to be considered when comparing it with racemic bupivacaine1 or ropivacaine.6 In a third paper, it was mentioned in the methodology that bupivacaine hydrochloride was compared with levobupivacaine base.2 The authors of the other papers, along with the majority of authors of published studies of levobupivacaine appear not to have considered that the label of the commercially available levobupivacaine (Chirocaine®) indicates the concentration of the base of the molecule, and not, as in the case of other amide-linked local anaesthetics such as racemic bupivacaine and ropivacaine, the concentration of the hydrochloride of the molecule.
Since the molecular weight of hydrogen chloride is 36.46, it will make a difference of 12.6% in the concentration of levobupivacaine between a concentration calculated as base or hydrochloride. It follows that, for example 5 mg ml1 (0.5%) concentration of levobupivacaine base is equivalent to 5.63 mg ml1 (0.563%) of levobupivacaine hydrochloride, which is then erroneously compared with 5 mg ml1 of ropivacaine or bupivacaine hydrochloride in the studies.
Although this has been pointed as early as in 1998 in this journal,1 and again by Schug in another anaesthesia journal in 2001,10 and the commercial product label of Chirocaine® clearly states the concentration of the base of the molecule, the 12.6% difference in concentration seems still to be ignored both by investigators and clinicians. As a consequence, the results of levobupivacaine compared with the same concentration of bupivacaine or ropivacaine in most regional anesthetic block studies need to be reinterpreted. It is of note that some of these studies have identified a 17% (P<0.04)6 and a 19% (not significant)11 potency difference in favour of levobupivacaine, which might be partially explained by this erroneous calculation.
1 Helsinki, Finland
2 Perth, Australia
References
1 Lyons G, Columb M, Wilson RC, Johnson RV. Epidural pain relief in labour: potencies of levobupivacaine and racemic bupivacaine. Br J Anaesth 1998; 81: 899901
2 Bay-Nielsen M, Klarskov B, Bech K, Andersen J, Kehlet H. Levobupivacaine vs bupivacaine as infiltration anaesthesia in inguinal herniorrhaphy. Br J Anaesth 1999; 82: 2802
3 Breebaart MB, Vercauteren MP, Hoffmann VL, Adriaensen HA. Urinary bladder scanning after day-case arthroscopy under spinal anaesthesia: comparison between lidocaine, ropivacaine, and levobupivacaine. Br J Anaesth 2003; 90: 30913
4 Gautier P, De Kock M, Huberty L, Demir T, Izydorczic M, Vanderick B. Comparison of the effects of intrathecal ropivacaine, levobupivacaine, and bupivacaine for Caesarean section. Br J Anaesth 2003; 91: 6849
5 McLeod GA. Density of spinal anaesthetic solutions of bupivacaine, levobupivacaine, and ropivacaine with and without dextrose. Br J Anaesth 2004; 92: 54751
6 Camorcia M, Capogna G, Lyons G, Columb M. Epidural test dose with levobupivacaine and ropivacaine: determination of ED50 motor block after spinal administration. Br J Anaesth 2004; 92: 8503
7 Leonard SA, Lydon A, Walsh M, Fleming C, Boylan J, Shorten GD. Does prior administration of enoxaparin influence the effects of levobupivacaine on blood clotting? Assessment using the Thromboelastograph®. Br J Anaesth 2001; 86: 80813
8 Chalkiadis GA, Eyres RL, Cranswick N, Taylor RH, Austin S. Pharmacokinetics of levobupivacaine 0.25% following caudal administration in children under 2 yr of age. Br J Anaesth 2004; 92: 21822
9 Simon MJG, Veering BT, Stienstra R, van Kleef JW, Burm AGL. Effect of age on the clinical profile and systemic absorption and disposition of levobupivacaine after epidural administration. Br J Anaesth 2004; 93: 51220
10 Schug SA. Correction factor for comparisons between levobupivacaine and racemic bupivacaine. Reg Anesth Pain Med 2001; 26: 91[CrossRef][ISI][Medline]
11 Benhamou D, Ghosh C, Mercier FJ. A randomized sequential allocation study to determine the minimum effective analgesic concentration of levobupivacaine and ropivacaine in patients receiving epidural analgesia for labor. Anesthesiology 2003; 99: 13836[CrossRef][ISI][Medline]
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