Investigations on the flucloxacillin levels in human serum, lung tissue, pericardial fluid and heart tissue.

Following intramuscular administration of 500 mg flucloxacillin, the levels of this antibiotic were measured in the serum, lung, and heart tissue as well as pericardial fluid obtained during 24 lung and 19 heart operations. Between 55 and 160 min following administration, the intact, inflamed, and tumorous lung tissue pieces contained 3.3-4.0, 2.0-2.7, and 1.5-2.4 mcg/g flucloxacillin, respectively, representing 16-36, 13-16, and 10-18% of the actual serum levels. Pericardial fluid contained practically no flucloxacillin. The cardiac auricle contained 2.3-3.5 mcg/g between 35 and 130 min after administration; the mitral valve showed 1.1-2.5 mcg/g between 90 and 170 min afterward, whereas in the aortic valve 1.6 mcg/g was found between 105-220 min later. These concentrations represented 16-20, 7-22, and 12% of the actual serum levels. Both the serum and tissue levels proved to be higher than those of oxacillin at the same dosage. The flucloxacillin levels of the serum and tissues studied were much higher than the minimum inhibiting concentrations for the sensitive bacteria. Therefore, flucloxacillin is considered an excellent antibiotic for the treatment of respiratory infections and endocarditis, whereas its levels in the pericardial fluid show it insufficient for treatment of pericarditis.