Antibiotic concentrations in human parapneumonic effusions

Simultaneous pleural fluid and serum antibiotic concentrations were determined in 16 patients (five with pleural empyema, nine with uncomplicated parapneumonic effusions and two with malignant effusions). All patients were receiving either a penicillin or a cephalosporin derivative. Concentrations of other antibiotics that the patients were receiving were also measured. Antibiotics penetrated well into pleural fluid. Antibiotic concentrations in pleural fluid were usually three-fourths or more of the concentrations in simultaneously obtained samples of serum, and the absolute pleural fluid concentrations were sufficient in most cases to inhibit the common aetiologic agents of the uncomplicated parapneumonic effusions and empyema. Standard systemic doses of antibiotics provide adequate pleural fluid concentrations in empyemas and uncomplicated parapneumonic effusions. The data support the practice of using only parenteral antibiotic therapy in the treatment of empyema or uncomplicated parapneumonic effusions. Direct intrapleural instillation of antibiotics appears superfluous.