CLEARANCE OF GENTAMICIN DURING CARDIAC-SURGERY

Treatment with an aminoglycoside plus flucloxacillin is commonly used to prevent wound infection and endocarditis after cardiac surgery. Car diopulmonary bypass, blood transfusion and the lack of a steady state greatly affect handling of gentamicin. Urinary gentamicin excretion is not predictable in terms of preoperative risk factors possibly becaus e there is no clear relationship between serum levels and gentamicin c learance. A study was performed to determine whether the existing prop hylactic regimen gave adequate serum levels during surgery and to comp are renal excretion of gentamicin and the trough serum levels. Ten pat ients received gentamicin (1.5 mg/kg at the start of surgery followed by 80 mg tds for 2 days) and flucloxacillin 500 mg qds for 2 days. Ser um and urinary concentrations of gentamicin were assayed during surger y and in the early postoperative period. The median apparent serum hal f-life during the first 8 h was 2.5 h (95%CI 1.7-3.2 h). The median ge ntamicin clearance was 37 mL/min (95%CI 23-64 mL/min) and the creatini ne clearance 85 mL/min (95%CI 72-210 mL/min). Serum levels remained ab ove 1 mg/L during surgery but urinary concentrations varied between 0. 4 and 364 mg/L (median 70 mg/L). At 24 h (but not 8 or 16 h), trough s erum levels appeared to be related to the amount of gentamicin excrete d but the relationship was not quite statistically significant (P = 0. 057). Despite the effects of cardiopulmonary bypass, therapeutic serum gentamicin levels were maintained during surgery and reduced renal ex cretion in the postoperative period was associated with raised levels.