Pharmacokinetics of ampicillin and sulbactam in patients undergoing heart surgery

The pharmacokinetics of ampicillin and sulbactam, a new beta-lactamase inhibitor, were investigated in 16 patients undergoing prosthetic cardiac valve insertion. The combination of 2 g of ampicillin and 1 g of sulbactam was administered as perioperative prophylaxis intravenously over 3 to 6 days. Several serum pharmacokinetic parameters were similar for the two drugs after three intravenous doses were given to patients following surgery. The half-lives of elimination of ampicillin and sulbactam were 79 +/- 4.9 and 88 +/- 5.9 min, the volumes of distribution were 15.6 +/- 1.4 and 17.7 +/- 1.2 liters/70 kg, and the total plasma clearances were 144.4 +/- 14.5 and 147.2 +/- 14.5 ml/min, respectively. The peak concentrations of ampicillin and sulbactam in serum were calculated to be 134.3 +/- 1.3 and 58.3 +/- 1.2 micrograms/ml, respectively. Ampicillin and sulbactam rapidly penetrated from the blood into various tissues collected during heart surgery, such as sternum, pericardium, myocardium, and endocardium. The concentrations of ampicillin in tissue ranged from 17.8 +/- 9.9 to 50 +/- 29.5 micrograms/g, and those of sulbactam in tissue ranged from 8.8 +/- 6.2 to 19.6 +/- 10.1 micrograms/g. The concentrations of ampicillin and sulbactam in serum and tissue also apparently exceeded the MICs against most beta-lactamase-producing bacteria usually involved in postoperative wound infections and prosthetic valve endocarditis. The ratio of the two compounds was approximately 2:1 in serum and in the various tissues affected by the operation. The pharmacokinetics of ampicillin and sulbactam in serum and investigated tissues suggest that the combination of the two beta-lactams will be effective in the perioperative prophylaxis of patients undergoing heart surgery.