Penetration of enoxacin into bronchial secretions

Enoxacin is a potent quinolone derivative with marked activity against gram-negative bacteria and staphylococci. The oral preparation has a potential role in treatment of gram-negative-bacterial lower respiratory infections if found to give adequate bronchial (sputum) concentrations. A study was done to determine the concomitant serum and bronchial concentrations of oral enoxacin after dosing with 600 mg, single dose; 400 mg, single dose; and 400 mg every 12 h, four doses. Blood and bronchial secretions were collected from 20 patients predose and 2, 5, and 9 h postdose. Bronchial secretions were obtained from tracheostomies, endotracheal tubes, or bronchoscopy. Levels of enoxacin in serum and sputum were measured by high-pressure liquid chromatography. Mean peak bronchial secretion levels were similar for the 400-mg dose schedules (2.2 and 2.4 micrograms/ml) but were significantly higher with the 600-mg dose (4.0 micrograms/ml) (P less than 0.05). Significant concentrations in bronchial secretions were still achievable at 9 h postdose (1.3 to 2.3 micrograms of enoxacin per ml). The mean ratios of enoxacin concentrations in sputum to those in serum at various time intervals for all groups were as follows: at 2 h, 0.55 +/- 0.34; at 5 h, 1.04 +/- 0.72; at 9 h, 0.97 +/- 0.62. Considering that most gram-negative bacteria are inhibited by 1.0 microgram of enoxacin per ml in vitro, this study shows that oral enoxacin in practical doses achieves a concentration in bronchial secretions that is adequate to treat most gram-negative-bacterial lower respiratory infections.