An evaluation of the perioperative efficacy of selective beta 1-blockade in coronary surgery. Studies with a late preoperative dose of metoprolol

The plasma concentration of metoprolol was measured hourly following an oral dose on two consecutive days--the day before, and the day of, coronary surgery. No significant difference was found between the two sampling days, though there was a tendency to lower concentrations during and after extracorporeal circulation. After a median dose of 50 mg the peak concentration (reached on average after 1.5 h) was 545 +/- 70 nmol/l on the first day and 388 +/- 57 on the day of surgery. The respective elimination rates from plasma, expressed as half-life, were 3.4 +/- 0.21 and 3.5 +/- 0.19 hours (NS). On the day of surgery the heart rate rose during the second half of the observation period, peaking above 130 beats/min. Heart rate was inversely correlated to metoprolol concentration in plasma with coefficient -0.68 before induction of anesthesia and -0.77 two hours after termination of extracorporeal circulation. The perioperative efficacy of beta-blockade following a late preoperative oral dose of the agent thus appeared to be reduced and inadequate.