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Taking the ‘sting’ out of local anaesthetics

Summary 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.