Subcutaneous infiltration with ammonium sulphate 10% does not prolong the local anaesthetic duration of lidocaine in humans.

Abstract

The aim of the present study was to investigate whether a solution of ammonium sulphate and lidocaine had a prolonged duration of action compared with lidocaine alone after subcutaneous infiltration in human volunteers. In a double-blind, randomised, controlled trial 12 male volunteers had either 4 ml lidocaine 1% (40 mg) or a solution of 4 ml ammonium sulphate 10% and lidocaine 1% (40 mg) subcutaneously infiltrated in corresponding skin areas on the right and left calf. The duration of the local anaesthetic action of the test medications was assessed 1-6 h after the infiltrations using thresholds to mechanical (von Frey hairs) and thermal stimulation (heat detection thresholds: HDT, and heat pain detection thresholds: HPDT), and by calculation of areas under the curve (AUC) for electronic visual analogue scale (VAS) pain ratings (sampled at 2 Hz) during a heat stimulation on the test areas for 30 s with a 45 degrees C warm thermode. At no assessment were thresholds to mechanical or thermal stimulation increased in favour of ammonium sulphate treated legs compared with control legs. On the contrary, HPDT were significantly lower in ammonium sulphate treated legs than control legs at the 3 h and 4 h assessment after infiltration (P<0.02). Similarly, the AUC for the VAS ratings was significantly higher in treatment legs compared with control legs 2 h and 3 h after infiltration (P<0.05). No improvement in local anaesthetic duration of ammonium sulphate 10% plus lidocaine 1% compared with lidocaine 1% alone was demonstrated early after subcutaneous infiltration in human volunteers.