Taking the 'sting' out of local anaesthetics.

In order to investigate factors influencing the discomfort caused by the injection of different lignocaine preparations, a randomized, double-blind comparison of paired injections was performed in 32 patients. In all subjects 2% plain lignocaine was found to be more painful than 0.5% plain lignocaine. Lignocaine with adrenaline 1:200,000 was found to be significantly more painful than plain lignocaine. The presence of sodium metabisulphite (the antioxidant in commercial adrenalized lignocaine) significantly increased the discomfort. Neutralization of acidic 0.5% lignocaine (pH 4.7) reduced the discomfort caused in 44% of patients, but this was not statistically significant.