Effects of salicylates and paracetamol compared to lidocaine on nerve conduction in vitro.

The effects of acetylsalicylic acid, salicylic acid, sodium salicylate and paracetamol on the compound action potentials of the isolated left phrenic nerve of the rat were observed, and compared to that of lidocaine. All drugs depressed the compound action potential in a reversible, dose-dependent way. Lidocaine (inhibition between 0.05 and 10 mM) was more potent than the other drugs and the depression occurred faster. The inhibitory effects of acetylsalicylic acid and salicylic acid were similar to each other (between 1 and 20 mM). Sodium salicylate was less potent (inhibition between 5 and 70 mM). These concentrations cover the plasma levels reported after therapeutic and toxic doses for the salicylates. Inhibition of nerve conduction may therefore contribute to the adverse nervous effects seen after intoxication with salicylates. In contrast, the observed concentrations for inhibition of the compound action potential caused by paracetamol (between 6.7 and 53 mM) were far greater than the plasma concentrations reported after therapeutic doses or after intoxication with paracetamol. Thus, the inhibition of the compound action potential, caused by paracetamol does not contribute to the therapeutic analgesic effects of paracetamol.