Absorption of lignocaine and bupivacaine from the upper and lower respiratory tract was studied in patients undergoing fibreoptic bronchoscopy. No significant differences were found between the drugs and between the routes of administration in terms of the time taken to achieve maximum plasma concentrations. The relative availability of lignocaine was greater following administration via the upper respiratory tract, but bupivacaine availability did not differ. The apparent clearance of lignocaine was not affected by the route of administration but bupivacaine clearance was higher following administration via the lower respiratory tract. Bupivacaine, previously unreported as a topical agent in man, produced adequate anaesthesia at one‐eighth of the dose of lignocaine. Plasma bupivacaine concentrations had a very wide safety margin.

Lignocaine metabolites are known to have both antiarrhythmic and toxic effects. Large plasma concentrations of these metabolites have been reported following endotracheal instillation of lignocaine. We measured plasma lignocaine monoethylglycinexylidide (MEGX), and glycinexylidide (GX) concentrations for up to 4h after fibreoptic bronchoscopy. The total dose of lignocaine required to suppress coughing varied between 230 mg and 364 mg. Small therapeutic lignocaine concentrations occurred transiently in nine of 19 patients after the bronchoscopy examination had finished. Only one patient achieved a plasma lignocaine concentration in the range of minor toxicity. Metabolite peaks occurred later and were of much smaller magnitude. They were unlikely to contribute to prophylaxis of cardiac arrhythmia or to toxicity. It would seem to be safe to use topical lignocaine in doses greater than the currently recommended maximum (200 mg) in conscious patients during fibreoptic bronchoscopy.