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 wi
th adrenaline (400 mu g) was studied on capsaicin-induced cough in 10
healthy subjects. Results - Cough was significantly reduced between fi
ve and 25 minutes by lignocaine. Adrenaline alone had no inhibitory ef
fect 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 diff
erent sensory mechanisms for anaesthesia and cough suppression. Plasma
concentrations of lignocaine were low (<30 ng/ml), not altered by adr
enaline, and did not correlate with the local anaesthetic or the antit
ussive 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.