A comparison of the hydrochloride salts of lignocaine and prilocaine for epidural analgesia.

Lumbar epidural blockade has been used in 317 subjects to compare the analgesic properties of the hydrochloride salts of lignocaine and prilocaine in 2 per cent and 3 per cent concentrations, with and without 1/200,000 adrenaline. Prilocaine has a slower onset and spread of analgesia than lignocaine. Duration of action and intensity of motor blockade is greater with plain prilocaine than with plain lignocaine in both 2 and 3 per cent concentrations. Addition of a vasoconstrictor improves the duration and quality of blockade of both prilocaine and lignocaine, but the effect on the latter is greater than on the former. The proportionate effect is such that the intensity of motor block and duration become practically the same in the 2 and 3 per cent solutions of both drugs when 1/200,000 adrenaline is present. At any given age all the test solutions, except 3 per cent plain prilocaine, produce the same degree of segmental spread. The dose-requirements of 3 per cent plain prilocaine are about 40 per cent greater than the other solutions at 20 years, but this difference decreases with age, and disappears by the ninth decade. Three per cent lignocaine with adrenaline produces the most efficient blockade of all the test solutions. However, the lower toxicity of prilocaine makes 3 per cent prilocaine with adrenaline the solution of choice in most instances.