[Is the plasma protein binding of lidocaine modified by the simultaneous administration of midazolam?]

Perioperative antiarrhythmic therapy with lidocaine (bolus dosage 100 mg followed by infusion of 200 mg/h) was performed in 24 patients; 12 of them simultaneously received an intravenous injection of 10 mg midazolam with the bolus of lidocaine (group I: with midazolam; group II: without midazolam). Central venous blood samples were collected over a period of 1 h (1, 3, 5, 10, 20, 30, and 60 min after the bolus) to evaluate unbound and total (protein-bound + unbound) plasma concentrations of lidocaine, thus calculating plasma protein binding. One minute after intravenous administration of lidocaine peak plasma concentrations occurred: in group I 5.38 +/- 1.99 micrograms/ml (mean +/- SD), in group II 5.25 +/- 1.90. Up to 60 min there was only a gradual decrease in plasma concentrations in both groups. There was no significant difference between the two groups (group I: mean free concentration 0.67-0.80 micrograms/ml; mean total concentration 4.84-5.38 micrograms/ml; mean plasma protein binding 83%-86%; group II: 0.69-0.89 micrograms/ml; 4.62-5.25 micrograms/ml; 82%-85%). We draw the conclusion that midazolam administration is safe in patients undergoing antiarrhythmic therapy or regional anesthesia with lidocaine.