The pharmacokinetic parameters of 16 patients in the intensive care unit, sedated with midazolam, were evaluated. A large variation was observed in the plasma concentration of midazolam and between the plasma concentration of midazolam and its metabolite 1-hydroxymethylmidazolam glucuronide. The plasma albumin concentration governs the volume of distribution of midazolam. Decreased plasma albumin concentration (25 gm/L) results in an increased volume of distribution and a decreased elimination rate of midazolam. The observed plasma concentration ratio between the parent drug and its metabolite 1-hydroxymethylmidazolam glucuronide is governed by the variables of protein binding, the metabolic rate of midazolam, and the renal clearance of the glucuronide metabolite itself (which can be considered as a measure of the kidney function of the patient).

The clinical effects and pharmacokinetics of 24 h infusion of midazolam (MDZ) during major maxillofacial surgery and postoperative observation in an Intensive Care Unit (ICU) were studied in 20 patients. During anaesthesia, infusion of MDZ at 5 mg/h combined with 67% nitrous oxide, 1.8 (s.d. = 0.8) mg of fentanyl, and 26.5 (s.d. = 11.4) mg of vecuronium, adequately suppressed clinical responses to surgical nociceptive stimuli. Postoperatively, infusion of MDZ was continued in the ICU at 5 mg/h until 9 a.m. of the first postoperative day for sedation of the intubated but spontaneously breathing patients. The depth of sedation in the ICU was scored from 1-5 (1 = "awake and tense", 5 = "unable to communicate"). During infusion the sedation score decreased from 3.8 after ICU arrival to 2.2 at 8 a.m. of the first postoperative day. Neither ventilatory nor circulatory depression were observed. After cessation of MDZ, recovery from sedation was fast. The degree of amnesia was low. During constant rate infusion no increase in plasma concentration of either MDZ or metabolites occurred. T1/2 beta of MDZ after cessation was 125 min (range 90-320) and its total body clearance was 10.5 ml/kg/min (s.d. = 3.1). The volume of distribution, clearance and T1/2 beta were significantly longer in women than in men. It was concluded that 24 h of MDZ infusion at 5 mg/h caused satisfactory ICU sedation with fast recovery, but that individual tailoring of the infusion rate may still improve the quality of sedation.

Seven intensive care patients were sedated with prolonged infusion of midazolam. One patient received a continuous infusion of midazolam for the treatment of status epilepticus. A bolus injection of 5 mg was administered, followed by infusion of 4-14 mg/hour depending on the required level of sedation. The length of infusion varied between 80 and 360 hours. The plasma concentrations of the midazolam during infusion were between 500-1000 ng/ml. All the patients were adequately sedated. The plasma elimination half-life of midazolam and its main metabolite, 1-0H-midazolam glucuronide, after stopping the infusion variedfrom 4-12 hours.