Analgesic responses to i.v. lignocaine.

The analgesic effect of i.v. lignocaine was evaluated in five patients with clinical neuralgic pain of varying aetiology. The response was compared with that on concurrently-induced ischaemic pain, initially of the same intensity. Following a high dose infusion of 3 mg kg-1 (lignocaine concentrations greater than 3 microgram ml-1) both pains were decreased, clinical pain to a significantly greater extent. Thereafter, at lower doses and blood concentrations, lignocaine was without effect on ischaemic pain, but almost totally suppressed the same patient's clinical pain. The results suggest a divergence in the specificity of the analgesic action of lignocaine i.v. according to the nature of the pain-inducing process. Disorders manifesting as deafferentation or central neuralgias appear to be affected favourably by lignocaine i.v. whereas pain of peripheral origin is unaffected by lignocaine, except at blood concentrations which approach toxic values.