Evaluation of cloxacillin concentrations in plasma and muscle tissue during cardiopulmonary bypass

Concentrations of cloxacillin in plasma and deep thoracic muscle tissue were measured in 10 patients who underwent elective coronary bypass surgery or valve replacement. One g of cloxacillin was administered after the induction of anaesthesia and 1 g cloxacillin was added to the oxygenator pump priming fluid before the start of the procedure. Blood and tissue samples were obtained before, during and after cardiopulmonary bypass. The relation between unbound plasma concentrations and total tissue contents of the drug was calculated. It was shown that measurement of the free plasma concentration may provide fairly reliable information on the free concentrations of cloxacillin in the tissues, and that determination of tissue contents may therefore not be necessary. Due to the administration of the second dose of cloxacillin at the start of cardiopulmonary bypass free tissue contents were just adequate in most patients. However, to obtain adequate tissue concentrations after bypass it is recommended that a third dose of the antibiotic be administered before the end of the operation.