It seems to be difficult for both clinicians and investigators to realize that there is a difference between the base and the salt of the drug molecule when local anaesthetic concentrations are reported. Di Donato and colleagues  have made an error when reporting the concentration of levobupivacaine in their paper published recently in EJA.
In contrast to the labelling principle of all other clinically used local anaesthetics the concentration of levobupivacaine (Chirocaine®) on the marketed ampoule is given as the concentration of the base-form of the molecule. Therefore, a 0.5% levobupivacaine concentration is, in fact, 0.56% when the concentration of the solution would be given according to the hydrochloride-form (salt) of the molecule, i.e., the form in which it exists in the injectable solution.
This error has been pointed out repeatedly in the anaesthesiology literature, the most recent note was published in 2005 .
Perhaps such a small error in actual levobupivacaine concentration does not make any difference in clinical practice, but this 12.6% difference may influence scientific evaluation and the interpretation of equipotency in comparison with other local anaesthetics. It can be assumed that the small difference in favour of levobupivacaine in the study by Di Donato and colleagues  would have been eliminated had the correct concentration (0.5% instead of 0.56%) and dose (45 mg instead of 50.4 mg) of levobupivacaine-HCl been chosen.
1. Di Donato A, Fontana C, Lancia F, Celleno D. Efficacy and comparison of 0.5% levobupivacaine with 0.75% ropivacaine for peribulbar anaesthesia in cataract surgery. Eur J Anaesthesiol
2. Rosenberg PH, Schug SA. Levobupivacaine base and levobupivacaine hydrochloride. Br J Anaesth