Measurement of pulmonary erythromycin concentration in patients with lobar pneumonia by means of positron tomography.

The concentration achieved in the infected tissue is of fundamental importance in the use of antibiotics. Erythromycin labelled with the positron-emitting nuclide carbon-11 and positron tomography were used to compare local concentrations of this antibiotic in the pneumonic and unaffected lungs of five patients with lobar pneumonia. The time course of uptake of erythromycin into the extravascular compartment (i.e., the intracellular, interstitial, and alveolar compartments) of the pneumonic lung was measured. The mean extravascular concentrations obtained during the first hour after an intravenous injection of 270 mg erythromycin lactobionate were similar in the pneumonic lung and the unaffected lung (5.5 +/- 2.2 and 6.6 +/- 2.2 micrograms/g, respectively). An effective concentration of erythromycin was reached in the pneumonic lung within 10 min of the injection and was maintained throughout the period of measurement (60 min).