Validation of fentanyl pharmacokinetics in patients undergoing coronary artery bypass grafting

Population Pharmacokinetics of Fentanyl in the Critically Ill

OBJECTIVE

To characterize fentanyl population pharmacokinetics in patients with critical illness and identify patient characteristics associated with altered fentanyl concentrations.

DESIGN

Prospective cohort study.

SETTING

Medical and surgical ICUs in a large tertiary care hospital in the United States.

PATIENTS

Patients with acute respiratory failure and/or shock who received fentanyl during the first 5 days of their ICU stay.

MEASUREMENTS AND MAIN RESULTS

We collected clinical and hourly drug administration data and measured fentanyl concentrations in plasma collected once daily for up to 5 days after enrollment. Among 337 patients, the mean duration of infusion was 58 hours at a median rate of 100 μg/hr. Using a nonlinear mixed-effects model implemented by NONMEM, we found that fentanyl pharmacokinetics were best described by a two-compartment model in which weight, severe liver disease, and congestive heart failure most affected fentanyl concentrations. For a patient population with a mean weight of 92 kg and no history of severe liver disease or congestive heart failure, the final model, which performed well in repeated 10-fold cross-validation, estimated total clearance, intercompartmental clearance (Q), and volumes of distribution for the central (V1) and peripheral compartments (V2) to be 35 L/hr (95% CI, 32-39 L/hr), 55 L/hr (95% CI, 42-68 L/hr), 203 L (95% CI, 140-266 L), and 523 L (95% CI, 428-618 L), respectively. Severity of illness was marginally associated with fentanyl pharmacokinetics but did not improve the model fit after liver and heart diseases were included.

CONCLUSIONS

In this study, fentanyl pharmacokinetics during critical illness were strongly influenced by severe liver disease, congestive heart failure, and weight, factors that should be considered when dosing fentanyl in the ICU. Future studies are needed to determine if data-driven fentanyl dosing algorithms can improve outcomes for ICU patients.

The population pharmacokinetics of fentanyl in patients undergoing living-donor liver transplantation

Fentanyl, an opioid analgesic with a high hepatic extraction ratio, is frequently used to supplement general anesthesia during liver transplantation and is also continuously infused to provide postoperative analgesia. However, because fentanyl is metabolized mainly in the liver, the pharmacokinetics of fentanyl may vary widely during the different phases of the surgery, potentially leading to adverse events. Using nonlinear mixed-effects modeling, we characterized the pharmacokinetics of fentanyl in 15 patients (American Society of Anesthesiologists Physical Status Classification 2 or 3) undergoing living-donor liver transplantation (LDLT). Fentanyl was continuously infused at the rate of 200-400 µg/h throughout the operation. The time course of the fentanyl plasma concentration levels was best described in terms of a two-compartment model. Estimates were made of the pharmacokinetic parameters during the preanhepatic, anhepatic, and neohepatic phases: central volume of distribution (V(1)) (l): 59.0 + hourly volume infused by rapid infusion system (RIS) × 42.5, 113.0, and 189.0, respectively, × (body weight/69)(1.3); peripheral volume of distribution (V(2)) (l): 94.3, 412.0, and 427.0, respectively; intercompartmental clearance (Q) (l/h): 96.4 × (cardiac output (CO)/6.7)(2.5), 22.6, and 28.2, respectively; metabolic clearance (Cl) (l/h): 21.7 during the preanhepatic and neohepatic phases, and 0 during the anhepatic phase. The preanhepatic central volume of distribution was found to be markedly influenced by the massive infusion of fluids and blood products. The more hyperdynamic the circulation was during the preanhepatic phase, the higher the distributional clearance.

Comparison of effects and plasma concentrations of opioids between elderly and middle-aged patients after cardiac surgery

BACKGROUND

In elderly patients, opioids may cause prominent postoperative sedation and respiratory depression. We evaluated the influence of age on the effects of opioids and plasma concentrations of fentanyl and oxycodone in cardiac surgery patients.

METHODS

Thirty (>or=75 years, gender M9/F21) and 20 (<or=60 years, gender M20/F0) patients scheduled to undergo cardiac surgery. A standard anesthesia with fentanyl as an opioid was used. Fentanyl plasma concentrations were measured at the end of surgery and 2 h later. After tracheal extubation, when the pain intensity was at least moderate, blood samples for fentanyl and oxycodone plasma concentration measurements were taken. Thereafter, oxycodone hydrochloride 0.05 mg/kg i.v. was administered. After 15 and 45 min, pain intensity, sedation and oxycodone plasma concentration were determined. This test protocol was repeated twice.

RESULTS

The elderly had a higher plasma concentration of fentanyl at the end of surgery than younger patients (5.7+/-2.2 vs. 3.8+/-1.2 ng/ml, P=0.001). The plasma concentrations of oxycodone were comparable between the groups. The interval between the second and the third oxycodone dose was longer in the elderly patients (P=0.036). Pain intensity on the verbal rating scale was lower at the 45-min assessment point after all three oxycodone test doses (P=0.008) and sedation scores were significantly higher after the third dose in the elderly patients (P=0.035).

CONCLUSIONS

In elderly patients, the plasma concentration of fentanyl was higher but plasma levels of oxycodone were at a similar level compared with middle-aged patients. However, the elderly patients had less pain and were more sedated after doses of oxycodone.