Pharmacokinetics of doxacurium during normothermic and hypothermic cardiopulmonary bypass surgery

Effect of cardiopulmonary bypass on cytochrome P450 enzyme activity: implications for pharmacotherapy

For patients undergoing cardiopulmonary bypass (CPB) during cardiac surgery, there are well-documented changes in the pharmacokinetics (PK) of commonly administered drugs. Although multiple factors potentially underpin these changes, there has been scant research attention on the impact of CPB to alter the activities of cytochrome P450 (CYP) isoenzymes. PK changes during cardiac surgery with CPB have the potential to adversely affect the safety and efficacy of pharmacotherapy and increase the risk of drug-drug interactions. Clinically significant changes in drug PK during CPB are likely to be prominent for drugs where CYP metabolism is a major clearance (CL) mechanism. However, clinical data from patients undergoing CPB surgery in support of this hypothesis are lacking, leaving a significant knowledge gap. In this review, we address the effects of CPB on the release of pro-inflammatory cytokines, in surgeries with and without CPB, both pre and post initiation of surgery. We reviewed literature to explore the relationship between the release of pro-inflammatory cytokines, and the expression and activities of CYP enzymes. Through this approach, we provide new insight on the effects of CPB on the PK of drugs administered to patients in the clinical setting. Future research to address this knowledge gap will have considerable impact to assist clinicians with optimizing pharmacotherapy in this patient population.

Pharmacokinetics of midazolam in critically ill pediatric patients

Midazolam is frequently used to produce sedation in critically ill pediatric patients. We studied the pharmacokinetics of midazolam in 22 patients (age 8 days to 16 years). The intravenous infusion rate to produce sedation ranged from 49-385 mcg/kg/hr. The blood samples were obtained at steady-state and midazolam was measured by gas chromatography with electron capture. The steady-state plasma concentrations of midazolam ranged from 49-385 ng/mL. The total clearance, apparent volume of distribution, and elimination half-life ranged from 0.1-3.1 L/kg/hr, 0.2-3.5 L/kg, and 0.3-10.9 hours, respectively. The marked interpatient variability in pharmacokinetics explains in part, the substantial variation in dosage requirements of midazolam to produce sedation in critically ill pediatric patients.