BACTERICIDAL ACTIVITY OF OXYBUPROCAINE AS A POTENTIAL SOURCE OF FALSE-NEGATIVE RESULTS OF BRONCHOALVEOLAR LAVAGE

New approaches in the diagnosis of pneumonia, especially in intensive care units, are quantitative cultures of bronchoalveolar (BAL) fluid o r the protected specimen brush. The sensitivity of these methods, howe ver, has often been found to be as low as 50-60%. One possible explana tion for the low sensitivity of these diagnostic tools is the antimicr obial activity of local anaesthetics used in bronchoscopy. Therefore, we investigated the bactericidal properties of oxybuprocaine, a topica l anaesthetic used for bronchoscopy in our clinic, in order to test th e reliability of specimens obtained from BAL. Methods. The bactericida l activity of oxybuprocaine in concentrations of 1%, 0.1%, 0.05% and 0 .01% was tested by constructing time-kill curves for Streptococcus pne umoniae, Hemophilus influenzae, Pseudomonas aeruginosa and Escherichia coli. Five stains of each bacterial species were tested. The inoculum size was 10(4) ml, and bacteria were counted after 10, 20, 30, 60 and 120 min. Results. The resulting time-kill curves are demonstrated in Figs, 1-4. The most sensitive bacteria were S. pneumoniae and H. influ enzae, in which significant bactericidal activity could be shown even with a 0.01% solution of oxybuprocaine. E. coli and P. aeruginosa were also inhibited, but only at the highest concentration of 1%. Conclusi ons. The use of local anaesthetics before material is taken for cultur e, e.g. from BAL, may give rise to false-negative results and should t herefore be avoided or reduced. For each local anaesthetic used in bro nchoscopy, the concentrations that can be used without the risk of fal se-negative results should be determined.