Comparative evaluation of the effects of lidocaine (lignocaine) hydrochloride and salicylate on nervous and Purkinje fibres.

Lidocaine hydrochloride and lidocaine salicylate (lisacaine) have been tested on the frog node of Ranvier, on the sheep cardiac Purkinje fibres and rat phrenic nerve-diaphragm. On the node of Ranvier both drugs produced the same degree of reduction of peak INa and steady-state potassium current and the same degree of shift of the steady-state inactivation curve for INa to more negative potential. Lisacaine took less time to reach the steady-state effect. On the cardiac Purkinje fibres both drugs decreased the action potential duration without any detectable difference; but their effects on V max (i.e. the maximum rate of depolarization) were different that of lisacaine being faster. On the rat phrenic nerve-diaphragm both drugs produced the same percentage of reduction of the contractile response of diaphragm but, the action of lisacaine was faster. Therefore the lidocaine molecule with the salicylate anion while displaying the same anaesthetic effectiveness has a faster action than the hydrochloride.