Antibiotic levels in empyemic pleural fluid

Objective: To determine the degree to which bioactive penicillin, metronida zole, ceftriaxone, clindamycin, vancomycin, and gentamicin penetrate into e mpyemic pleural fluid using our new rabbit model of empyema. Methods: An empyema was created via the intrapleural injection of 10(8) Pas teurella multocida bacteria into the pleural space of New Zealand white rab bits. After an empyema was verified by thoracentesis and pleural fluid anal ysis, penicillin, 24,000 U/kg; metronidazole, 37 mg/kg; ceftriaxone, 30 mg/ kg; clindamycin, 9 mdkg; vancomycin, 15 mg/kg; or gentamicin, 1 mg/kg, were administered IV. Antibiotic levels in samples of pleural fluid and serum, collected serially for up to 480 min, were then determined using a bioassay . Results: The degree to which the different antibiotics penetrated into the infected pleural space was highly variable. Penicillin penetrated most easi ly, followed by metronidazole, ceftriaxone, clindamycin, vancomycin, and ge ntamicin. Of the antibiotics tested, penicillin and metronidazole equilibra ted the most rapidly with the infected pleural fluid. Penicillin levels rem ained elevated in pleural fluid even after serum levels had decreased. Conclusions: Using this rabbit model of empyema, there was marked variation in the penetration of antibiotics into the empyemic fluid. Although there are species differences between rabbit and human pleura, the variance in de gree of penetration of antibiotics into the pleural space should be conside red when antibiotics are selected for the treatment of patients with empyem a.