Neurokinetics of lidocaine in the infraorbital nerve of the rat in vivo: relation to sensory block

Abstract

The kinetics of neural uptake and efflux of lidocaine hydrochloride were studied by means of a standardized technique for blocking the infraorbital nerve of the rat, using a palatal jig. Following injection of 14C labeled local anesthetic, groups of ten animals were sacrificed at incipient recovery from sensory block or at other times. The nerves were weighed and assayed for radioactivity. The lengths of nerve containing high levels of lidocaine varied inversely with the times elapsed since onset of block. In experiments where a fixed quantity (2 mg) of drug was injected, the incidence of block 2 hours later was concentration dependent, occurring in 80 per cent of animals after 2 per cent, in 40 per cent after 1 per cent, and in none after 0.5 per cent lidocaine. Epinephrine, 1:200,000, prolonged by 80 per cent the block effected with 0.2 ml of 1 per cent lidocaine. At the onset of recovery the neural contents of lidocaine at the sites of injection were 484±404 ng/mg of nerve in epinephrine treated nerves, and 274±218 ng/mg in nonepinephrine treated nerves (N.S., P> 0.05). Quantitative comparisons of in vivo effectiveness of local anesthetic solutions can be made with this technique.