Surface activities of procaine, lidocaine, and tetracaine and their interaction energies with phospholipid monolayers.

The free energies of adsorption of procaine, lidocaine, and tetracaine at the air--water interface were estimated from plots of surface pressure (pi less than or equal to 5 dynes/cm) against bulk concentration. Their interaction energies with dipalmitoylphosphatidylethanolamine and dipalmitoyllecithin monolayers, previously spread at the air--water interface, were estimated from the increase of surface pressure with increasing concentrations of the subphase-injected anesthetic. Free energies of adsorption and the interaction energies were in the order procaine less than lidocaine less than tetracaine and correlate with relative anesthetic potencies and the blocking of nerve conduction.