Sensitivity of respiratory bacteria to lignocaine

Lignocaine, a topical anaesthetic agent, is generally used in variable concentrations usually between 2% and 4% on the vocal cords prior to flexible bronchoscopy and bronchoalveolar lavage (BAL) procedures. The aim of this study was to investigate whether 2% or 1% lignocaine significantly inhibits the growth of organisms commonly found in the respiratory tract, in particular Streptococcus pneumoniae.

In order to determine the antibiotic effect of lignocaine on lower respiratory tract flora, five different organisms were examined in vitro using well diffusion, disc diffusion and microbroth dilution against 1% and 2% concentrations of lignocaine.

Antimicrobial activity could not be detected using the well diffusion and the disc diffusion methods, as lignocaine failed to diffuse through the media. The microbroth dilution method showed reproducible bactericidal effect of these respiratory isolates against Streptococcus pneumoniae, Moraxella catarrhalis and Haemophilus influenzae at 2% concentration. Lignocaine 2% showed no growth inhibition against Pseudomonas aeruginosa and Candida albicans. Lignocaine 1% also partially inhibited S. pneumoniae.

As lignocaine shows significant inhibition of respiratory pathogens such as Streptococcus pneumoniae even at a concentration of 1%, the lowest concentration possible should be used for flexible bronchoscopy and BAL to maximise the chance of recovery of these organisms.