Differential sensitivity of A and C nerve fibres to long-acting amide local anaesthetics.

The differential sensitivities of A beta, A delta and C fibres of rat vagus nerve to bupivacaine, etidocaine and AL-381 were studied in vitro. In A beta fibres, at 35-37 degrees C, 50 mumole litre-1 of the drugs had similar effects on the action potential amplitude, while at greater concentrations (100 and 200 mumole litre-1) the greatest mean depression of amplitude was seen with etidocaine (n.s.). AL-381 had the most marked effect on the A delta potentials, and it appeared that it was about twice as potent as the others in blocking these fibres. Etidocaine 100 mumole litre-1 was more depressant than the same dose of bupivacaine. The C fibres were blocked most rapidly by AL-381, while etidocaine had the least effect.