Effects of inhaled lignocaine and adrenaline on capsaicin-induced cough in humans.

BACKGROUND--The hypothesis that adrenaline can augment and/or prolong the antitussive effect of nebulised lignocaine was examined. METHODS--The effect of inhaled lignocaine alone (20 mg) and in combination with adrenaline (400 micrograms) was studied on capsaicin-induced cough in 10 healthy subjects. RESULTS--Cough was significantly reduced between five and 25 minutes by lignocaine. Adrenaline alone had no inhibitory effect and it neither augmented nor prolonged the antitussive effect of lignocaine. The subjective anaesthesia by lignocaine was short lasting (less than 15 minutes) and not altered by adrenaline, suggesting different sensory mechanisms for anaesthesia and cough suppression. Plasma concentrations of lignocaine were low (< 30 ng/ml), not altered by adrenaline, and did not correlate with the local anaesthetic or the antitussive effect. CONCLUSIONS--Lignocaine acts locally in the oropharynx and airways and adrenaline does not alter the effect or absorption of nebulised lignocaine on the human respiratory mucosa.