Comparative pharmacokinetics of fentanyl and alfentanil

Alfentanil versus fentanyl for emergency department rapid sequence induction with ketamine: A-FAKT, a pilot randomized trial

BACKGROUND

Fentanyl is often administered during rapid sequence induction of anesthesia (RSI) in the emergency department (ED) to ameliorate the hypertensive response that may occur. Due to its more rapid onset, the use of alfentanil may be more consistent with both the onset time of the sedative and the commencement of laryngoscopy. As such, we compared the effect of alfentanil and fentanyl on post-induction hemodynamic changes when administered as part of a standardized induction regimen including ketamine and rocuronium in ED RSI.

METHODS

This was a double-blind pilot randomized controlled trial of adult patients requiring RSI in the ED of three urban Australian hospitals. Patients were randomized to receive either alfentanil or fentanyl in addition to ketamine and rocuronium for RSI. Non-invasive blood pressure and heart rate were measured immediately before and at two, four, and six minutes after induction. The primary outcome was the occurrence of at least one post-induction systolic blood pressure outside the pre-specified range of 100-160mmHg (with adjustment for patients with baseline hypertension). Secondary outcomes included hypertension, hypotension, hypoxia, first-pass intubation success, 30-day mortality, and the pattern of hemodynamic changes.

RESULTS

A total of 61 patients were included in the final analysis (31 in the alfentanil group and 30 in the fentanyl group). The primary outcome was met in 58% of the alfentanil group and 50% of the fentanyl group (difference 8%, 95% confidence interval: -17% to 33%). The 30-day mortality rate, first-pass success rate, and incidences of hypertension, hypotension, and hypoxia were similar between the groups. There were no significant differences in systolic blood pressure or heart rate between the groups at any of the measured time-points.

CONCLUSION

Alfentanil and fentanyl produced comparable post-induction hemodynamic changes when used as adjuncts to ketamine in ED RSI. Future studies could consider comparing different dosages of these opioids.

Case report of pharmacokinetic analysis of continuous intravenous infusion of fentanyl in a patient with severe burn: burn shock stage complicates pain management

BACKGROUND

Fentanyl is widely used as an analgesic and sedative for patients with severe burn injuries in intensive care units. However, pharmacokinetic (PK) data for fentanyl, particularly for continuous intravenous infusion during the acute phase of burn injuries, are limited. Here, we report the clinical course and changes in blood fentanyl concentrations during the acute phase in a patient with severe burns treated with continuous intravenous infusion of fentanyl.

CASE PRESENTATION

A woman in her 40s, with burns caused by a gas cylinder explosion, was transported to our hospital. The patient had burn wounds on face, neck, shoulders, and all four extremities, with a total burn area of 39.0%. For pain relief, the patient received a continuous infusion of 0.01 mg/mL fentanyl (20-30 µg/h) with a target blood concentration of 1.0-1.5 ng/mL, but continued to suffer from pain due to burning during the acute phase. We measured the blood fentanyl concentrations and found that all concentrations obtained during the acute phase were subtherapeutic. Notably, during the burn shock stage, blood concentrations of fentanyl were 0.50 ng/mL on day 1 and 0.66 ng/mL on day 2, indicating that the blood concentration did not rise sufficiently for the dosage. From days 0 to 2, the patient was administered a massive fluid load for burn shock. After the burn shock stage resolved, fentanyl concentrations gradually approached the target range, and the pain rating scale improved, even though the fentanyl administration rate remained unchanged (30 µg/h).

CONCLUSIONS

Major changes in the fluid volumes of body compartments that occur with large burns might increase the volume of fentanyl distribution, thereby lowering its concentration when a standard dose is administered. Our findings indicate that the PK of fentanyl in patients with severe burns can be substantially affected, especially during the shock phase, implying the importance of titrating analgesics for clinical efficacy in the acute phase.

Multicenter Population Pharmacokinetics of Fentanyl in Neonatal Surgical Patients Using Dried Blood Spot Specimen Collection Demonstrates Maturation of Elimination Clearance

BACKGROUND

Fentanyl is widely used for analgesia and sedation in neonates, but pharmacokinetic (PK) analysis in this population has been limited by the relatively large sample volumes required for plasma-based assays.

METHODS

In this multicenter observational study of fentanyl kinetics in neonates up to 42 weeks of postmenstrual age (PMA) who received fentanyl boluses and continuous infusions, dried blood spots were used for small-volume sampling. A population PK analysis was used to describe fentanyl disposition in term and preterm neonates. Covariates for the model parameters, including body weight, PMA, birth status (preterm or term), and presence of congenital cardiac disease, were assessed in a stepwise manner.

RESULTS

Clearance was estimated to be greater than adult clearance of fentanyl and varied with weight. Covariate selection did not yield a significant relationship for age as a continuous or dichotomous variable (term or preterm, the latter defined as birth with PMA of <37 weeks) and clearance.

CONCLUSIONS

A supra-allometric effect on clearance was determined during covariate analyses (exponential scaling factor for body weight >0.75), as has been described in population PK models that account for maturation of intrinsic clearance (here, predominantly hepatic microsomal activity) in addition to scaling for weight, both of which impact clearance in this age group.

Evaluation of in vitro/in vivo correlations for three fentanyl transdermal delivery systems using in vitro skin permeation testing and human pharmacokinetic studies under the influence of transient heat application

The value of developing an in vitro/in vivo correlation (IVIVC) is substantial in biopharmaceutical drug development because once the model is developed and validated, an in vitro method may be used to efficiently assess and predict drug product performance in vivo. In this study, three bioequivalent, matrix-type, fentanyl transdermal delivery systems (TDS) were evaluated in vitro using an in vitro permeation test (IVPT) and dermatomed human skin, and in vivo in human pharmacokinetic (PK) studies under harmonized study designs to evaluate IVIVC. The study designs included 1 h of transient heat application (42 ± 2 °C) at either 11 h or 18 h after TDS application to concurrently investigate the influence of heat on drug bioavailability from TDS and the feasibility of IVPT to predict the effects of heat on TDS in vivo. Level A (point-to-point) and Level C (single point) IVIVCs were evaluated by using PK-based mathematical equations and building IVIVC models between in vitro fraction of drug permeation and in vivo fraction of drug absorption. The study results showed that the three differently formulated fentanyl TDS have comparable (p > 0.05) heat effects both in vitro and in vivo. In addition, the predicted steady-state concentration (C_ss) from in vitro flux data and the observed C_ss in vivo showed no significant differences (p > 0.05). However, the effects of heat on enhancement of fentanyl bioavailability observed in vivo were found to be greater compared to those observed in vitro for all three drug products, resulting in a weak prediction of the impact of heat on bioavailability from the in vitro data. The results from the current work suggest that while IVPT can be a useful tool to evaluate the performance of fentanyl TDS in vivo with a relatively good predictability at a normal temperature condition and to compare the effect of heat on drug delivery from differently formulated TDS, additional testing measures would enhance the ability to predict the heat effects in vivo with a lower prediction error.

Predicting Maternal-Fetal Disposition of Fentanyl Following Intravenous and Epidural Administration Using Physiologically Based Pharmacokinetic Modeling

Fentanyl is an opioid analgesic used to treat obstetrical pain in parturient women through epidural or intravenous route, and unfortunately can also be abused by pregnant women. Fentanyl is known to cross the placental barrier, but how the route of administration and time after dosing affects maternal-fetal disposition kinetics at different stages of pregnancy is not well characterized. To address this knowledge gap, we developed a maternal-fetal physiologically based pharmacokinetic (mf-PBPK) model for fentanyl to evaluate the feasibility to predict the maternal and fetal plasma concentration-time profiles of fentanyl after various dosing regimens. As fentanyl is typically given via the epidural route to control labor pain, an epidural dosing site was developed using alfentanil as a reference drug and extrapolated to fentanyl. Fetal hepatic clearance of fentanyl was predicted from CYP3A7-mediated norfentanyl formation in fetal liver microsomes (intrinsic clearance = 0.20 ± 0.05 µl/min/mg protein). The developed mf-PBPK model successfully captured fentanyl maternal and umbilical cord concentrations after epidural dosing and was used to simulate the concentrations after intravenous dosing (in a drug abuse situation). The distribution kinetics of fentanyl were found to have a considerable impact on the time course of maternal:umbilical cord concentration ratio and on interpretation of observed data. The data show that mf-PBPK modeling can be used successfully to predict maternal disposition, transplacental distribution, and fetal exposure to fentanyl. SIGNIFICANCE STATEMENT: This study establishes the modeling framework for predicting the time course of maternal and fetal exposures of fentanyl opioids from mf-PBPK modeling. The model was validated based on fentanyl exposure data collected during labor and delivery after intravenous or epidural dosing. The results show that mf-PBPK modeling is a useful predictive tool for assessing fetal exposures to fentanyl opioid therapeutic regimens and potentially can be extended to other drugs of abuse.

Comparison of: (2S,4R)-4-[18F]Fluoroglutamine, [11C]Methionine, and 2-Deoxy-2-[18F]Fluoro-D-Glucose and Two Small-Animal PET/CT Systems Imaging Rat Gliomas

Purpose

The three positron emission tomography (PET) imaging compounds: (2S,4R)-4-[¹⁸F]Fluoroglutamine ([¹⁸F]FGln), L-[methyl-¹¹C]Methionine ([¹¹C]Met), and 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) were investigated to contrast their ability to image orthotopic BT4C gliomas in BDIX rats. Two separate small animal imaging systems were compared for their tumor detection potential. Dynamic acquisition of [¹⁸F]FGln was evaluated with multiple pharmacokinetic models for future quantitative comparison.

Procedures

Up to four imaging studies were performed on each orthotopically grafted BT4C glioma-bearing BDIX rat subject (n = 16) on four consecutive days. First, a DOTAREM^® contrast enhanced MRI followed by attenuation correction CT and dynamic PET imaging with each radiopharmaceutical (20 min [¹¹C]Met, 60 min [¹⁸F]FDG, and 60 min [¹⁸F]FGln with either the Molecubes PET/CT (n = 5) or Inveon PET/CT cameras (n = 11). Ex vivo brain autoradiography was completed for each radiopharmaceutical and [¹⁸F]FGln pharmacokinetics were studied by injecting 40 MBq into healthy BDIX rats (n = 10) and collecting blood samples between 5 and 60 min. Erythrocyte uptake, plasma protein binding and plasma parent-fraction were combined to estimate the total blood bioavailability of [¹⁸F]FGln over time. The corrected PET-image blood data was then applied to multiple pharmacokinetic models.

Results

Average BT4C tumor-to-healthy brain tissue uptake ratios (TBR) for PET images reached maxima of: [¹⁸F]FGln TBR: 1.99 ± 0.19 (n = 13), [¹⁸F]FDG TBR: 1.41 ± 0.11 (n = 6), and [¹¹C]Met TBR: 1.08 ± 0.08, (n = 12) for the dynamic PET images. Pharmacokinetic modeling in dynamic [¹⁸F]FGln studies suggested both reversible and irreversible uptake play a similar role. Imaging with Inveon and Molecubes yielded similar end-result ratios with insignificant differences (p > 0.25).

Conclusions

In orthotopic BT4C gliomas, [¹⁸F]FGln may offer improved imaging versus [¹¹C]Met and [¹⁸F]FDG. No significant difference in normalized end-result data was found between the Inveon and Molecubes camera systems. Kinetic modelling of [¹⁸F]FGln uptake suggests that both reversible and irreversible uptake play an important role in BDIX rat pharmacokinetics.

Hydromorphone Compared to Fentanyl in Patients Receiving Extracorporeal Membrane Oxygenation

Fentanyl is commonly used in critically ill patients receiving extracorporeal membrane oxygenation (ECMO). Fentanyl's lipophilicity and protein binding may contribute to a sequestration of the drug in the ECMO circuit. Hydromorphone lacks these characteristics potentially leading to a more predictable drug delivery and improved pain and sedation management among ECMO patients. This study compared hydromorphone to fentanyl in patients receiving ECMO. This retrospective study included adult patients receiving ECMO for ≥48 hours. Patients were excluded if they required neuromuscular blockade, received both fentanyl and hydromorphone during therapy, or had opioid use before hospitalization. Baseline characteristics included patient demographics, ECMO indication and settings, and details regarding mechanical ventilation. The primary outcome was opioid requirements at 48 hours post cannulation described in morphine milligram equivalent (MME). Secondary endpoints included 24-hour opioid requirements, concurrent sedative use, and differences in pain and sedation scores. No differences were noted between the patients receiving fentanyl (n = 32) or hydromorphone (n = 20). Patients receiving hydromorphone required lower MME compared to fentanyl at 24 hours (88 [37-121] vs. 131 [137-227], p < 0.01) and 48 hours (168 [80-281] vs. 325 [270-449], p < 0.01). The proportion of within-goal pain and sedation scores between groups was similar at 24 and 48 hours. Sedative requirements did not differ between the groups. Patients receiving hydromorphone required less MME compared to fentanyl without any differences in sedative requirements, or agitation-sedation scores at 48 hours. Prospective studies should be completed to validate these findings.

Preterm Physiologically Based Pharmacokinetic Model. Part II: Applications of the Model to Predict Drug Pharmacokinetics in the Preterm Population

BACKGROUND

Preterm neonates are usually not part of a traditional drug development programme, however they are frequently administered medicines. Developing modelling and simulation tools, such as physiologically based pharmacokinetic (PBPK) models that incorporate developmental physiology and maturation of drug metabolism, can be used to predict drug exposure in this group of patients, and may help to optimize drug dose adjustment.

OBJECTIVE

The aim of this study was to assess and verify the predictability of a preterm PBPK model using compounds that undergo diverse renal and/or hepatic clearance based on the knowledge of their disposition in adults.

METHODS

A PBPK model was developed in the Simcyp Simulator V17 to predict the pharmacokinetics (PK) of drugs in preterm neonates. Drug parameters for alfentanil, midazolam, caffeine, ibuprofen, gentamicin and vancomycin were collated from the literature. Predicted PK parameters and profiles were compared against the observed data.

RESULTS

The preterm PBPK model predicted the PK changes of the six compounds using ontogeny functions for cytochrome P450 (CYP) 1A2, CYP2C9 and CYP3A4 after oral and intravenous administrations. For gentamicin and vancomycin, the maturation of renal function was able to predict the exposure of these two compounds after intravenous administration. All PK parameter predictions were within a twofold error criteria.

CONCLUSION

While the developed preterm model for the prediction of PK behaviour in preterm patients is not intended to replace clinical studies, it can potentially help with deciding on first-time dosing in this population and study design in the absence of clinical data.

Intranasal Fentanyl for Intervention-Associated Breakthrough Pain After Cardiac Surgery

Background

Cardiac bypass surgery patients have early postoperative interventions that elicit breakthrough pain. We evaluated the use of intranasal fentanyl for breakthrough pain management in these patients.

Methods

Multimodal analgesia (paracetamol 1 g three times a day, oxycodone 2–3 mg boluses with a patient-controlled intravenous pump) was used in 16 patients (age 49–70 years, weight 59–129 kg) after cardiac bypass surgery. Intranasal fentanyl 100 µg or 200 µg was used to manage breakthrough pain on the first and third postoperative mornings in a randomised order. Blood samples were collected for up to 3 h after fentanyl administration, pain was assessed with a numeric rating scale of 0–10. Plasma fentanyl concentration was assayed using liquid chromatography-mass spectrometry. Body composition was measured with a bioelectrical impedance device.

Results

Bioavailability of intranasal fentanyl was high (77%), absorption half-time short (< 2 min) and an analgesic plasma concentration ≥ 0.5 ng/mL was achieved in 31 of 32 administrations. Fentanyl exposure correlated inversely with skeletal muscle mass and total body water. Fentanyl analgesia was effective both on the first postoperative morning with chest pleural tube removal and during physiotherapy on the third postoperative morning. The median time of subsequent oxycodone administration was 1.1 h after intranasal fentanyl 100 µg and 2.1 h after intranasal fentanyl 200 µg, despite similar oxycodone concentrations (median 13.8, range 5.2–35 ng/mL) in both fentanyl dose groups.

Conclusions

Intranasal fentanyl 100 µg provided rapid-onset analgesia within 10 min and is an appropriate starting dose for incidental breakthrough pain in the first 3 postoperative days after cardiac bypass surgery.

Clinical Trial Registration

EudraCT Number: 2018-001280-22.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40262-021-01002-4.

Factors Contributing to Fentanyl Pharmacokinetic Variability Among Diagnostically Diverse Critically Ill Children

OBJECTIVE

The objective of this study was to characterize the population pharmacokinetics of fentanyl and identify factors that contribute to exposure variability in critically ill pediatric patients.

METHODS

We conducted a single-center, retrospective cohort study using electronic record data and remnant blood samples in the setting of a mixed medical/surgical intensive care unit (ICU) at a quaternary children's hospital. Children with a predicted ICU length of stay of at least 3 days and presence of an indwelling central venous or arterial line were included. Serum fentanyl measurements were performed for 278 unique remnant samples from 66 patients. Both one- and two-compartment models were evaluated to describe fentanyl disposition. Covariates were introduced into the model in a forward/backward, stepwise approach and included age, sex, race, weight, cytochrome P450 (CYP) 3A5 genotype, and the presence of CYP3A4 or CYP3A5 inducers or inhibitors. Simulations were performed using the successful model to depict the influence of inducers on fentanyl concentrations.

RESULTS

A two-compartment base model best described the data. There was good agreement between observed and predicted concentrations in the final model. The typical fentanyl clearance for 70 kg (reference weight) and 20.1 kg (median weight) patients were 34.6 and 13.6 L/h, respectively. The magnitude of the unexplained random inter-individual variability was high for both clearance (60.7%) and apparent volume of the central compartment (V₁) (107.2%). Coadministration of the known CYP3A4/5 inducers fosphenytoin and/or phenobarbital was associated with significantly increased fentanyl clearance. Simulations demonstrate that the effect of inducer administration was most pronounced following discontinuation of a fentanyl infusion.

CONCLUSIONS

In this study we show the feasibility and utility of using electronic record data and remnant blood samples to successfully construct population pharmacokinetic models for a heterogeneous cohort of critically ill children. A clinically relevant effect of concomitant CYP3A4/5 inducers was identified. Scaling this population pharmacokinetic approach is necessary to craft precision approaches to fentanyl administration for critically ill children.

(2S, 4R)-4-[18F]Fluoroglutamine for In vivo PET Imaging of Glioma Xenografts in Mice: an Evaluation of Multiple Pharmacokinetic Models

PURPOSE

The glutamine analogue (2S, 4R)-4-[18F]fluoroglutamine ([18F]FGln) was investigated to further characterize its pharmacokinetics and acquire in vivo positron emission tomography (PET) images of separate orthotopic and subcutaneous glioma xenografts in mice.

PROCEDURES

[18F]FGln was synthesized at a high radiochemical purity as analyzed by high-performance liquid chromatography. An orthotopic model was created by injecting luciferase-expressing patient-derived BT3 glioma cells into the right hemisphere of BALB/cOlaHsd-Foxn1nu mouse brains (tumor growth monitored via in vivo bioluminescence), the subcutaneous model by injecting rat BT4C glioma cells into the flank and neck regions of Foxn1nu/nu mice. Dynamic PET images were acquired after injecting 10-12 MBq of the tracer into mouse tail veins. Animals were sacrificed 63 min after tracer injection, and ex vivo biodistributions were measured. Tumors and whole brains (with tumors) were cryosectioned, autoradiographed, and stained with hematoxylin-eosin. All images were analyzed with CARIMAS software. Blood sampling of 6 Foxn1nu/nu and 6 C57BL/6J mice was performed after 9-14 MBq of tracer was injected at time points between 5 and 60 min then assayed for erythrocyte uptake, plasma protein binding, and plasma parent-fraction of radioactivity to correct PET image-derived whole-blood radioactivity and apply the data to multiple pharmacokinetic models.

RESULTS

Orthotopic human glioma xenografts displayed PET image tumor-to-healthy brain region ratio of 3.6 and 4.8 while subcutaneously xenografted BT4C gliomas displayed (n = 12) a tumor-to-muscle (flank) ratio of 1.9 ± 0.7 (range 1.3-3.4). Using PET image-derived blood radioactivity corrected by population-based stability analyses, tumor uptake pharmacokinetics fit Logan and Yokoi modeling for reversible uptake.

CONCLUSIONS

The results reinforce that [18F]FGln has preferential uptake in glioma tissue versus that of corresponding healthy tissue and fits well with reversible uptake models.

Dosing of Continuous Fentanyl Infusions in Obese Children: A Population Pharmacokinetic Analysis

Differences in fentanyl pharmacokinetics (PK) between obese and nonobese adults have previously been reported; however, the impact of childhood obesity on fentanyl PK is relatively unknown. We developed a population pharmacokinetic (PopPK) model using opportunistically collected samples from a cohort of predominately obese children receiving fentanyl per the standard of care. Using a probability-based approach, we evaluated the ability of different continuous infusion strategies to provide steady-state concentrations (Css ) within an analgesic concentration range (1-3 ng/mL). Fifty-three samples from 32 children were used for PopPK model development. Median (range) age and body weight of study participants were 13 years (2-19 years) and 52 kg (16-164 kg), respectively. The majority of children (94%) were obese. A 2-compartment model allometrically scaled by total body weight provided an appropriate fit to the data. Estimated typical clearance was 32.5 L/h (scaled to 70 kg). A fixed dose rate infusion of 1 µg/kg/h was associated with probabilities between 49% and 58% for achieving Css within target; however, the risk of achieving Css > 3 ng/mL increased with increasing body weight (15% at 16 kg vs 43% at 164 kg). A proposed model-based infusion strategy maintained consistent probabilities across the examined weight range for achieving Css within (58%) and above (20%) target. Use of an allometric relationship between weight and clearance was appropriate for describing the PK of intravenous fentanyl in our cohort of predominately obese children. Our proposed model-derived continuous infusion strategy maximized the probability of achieving target Css in children of varying weights.

Sedative and Analgesic Drug Sequestration After a Single Bolus Injection in an Ex Vivo Extracorporeal Membrane Oxygenation Infant Circuit

Patient sedation and analgesia on extracorporeal membrane oxygenation (ECMO) is vital for safety and comfort. However, adsorption to the circuit may alter drug pharmacokinetics and remains poorly characterized. This study characterizes drug adsorption of morphine, fentanyl, midazolam, and dexmedetomidine in an ex vivo infant ECMO circuit utilizing polymethylpentene (PMP) membrane oxygenator (MO) with protein-bounded polyvinylchloride (PVC) tubing. Twelve closed-loop ex vivo ECMO circuits were prepared using P.h.i.s.i.o (phosphorylcholine)-coated PVC tubing (Sorin Group USA, Inc.) and a Quadrox-iD pediatric polymethylpentene MO (Maquet Cardiopulmonary AG). Once the circuits were primed and running, a single medication was injected as a bolus into the circuit with three circuits per drug. Drug samples were drawn following injection, at 2, 5, 15, 30, 60, 120 minutes and at 4, 12, 24, 36, and 48 hours and analyzed using ultra high-performance liquid chromatography with mass spectrometry. Compared with morphine, the other drugs are highly sequestered with fentanyl 68.5%, dexmedetomidine 50.8%, and midazolam 26.2% affecting the availability of free drug in the circuit. Sequestration of fentanyl, midazolam, and dexmedetomidine in an ECMO circuit with P.h.i.s.i.o-coated PVC tubing and PMP MO may limit drug delivery to infants. Future in vivo studies are needed to determine the clinical impact of sequestration.

Fast increase of postmortem fentanyl blood concentrations after transdermal application: A call to careful interpretation

BACKGROUND

Interpretation of postmortem fentanyl concentrations after transdermal application remains a challenge. There are indications that fentanyl shows relevant postmortem redistribution. The aim of this study was to investigate the time course of these changes and to develop recommendations for toxicological case work.

MATERIAL AND METHOD

Blood specimens were collected from palliative care patients who were treated with fentanyl transdermal patches. Antemortem reference samples (ethylenediaminetetraacetic acid (EDTA) and serum specimens) were collected at stable dose rates. Postmortem femoral venous blood specimens were collected at four postmortem time-points: 2hpm (hours postmortem), 6-8hpm, 11-16hpm and approximately 24hpm. Liquid chromatography tandem mass spectrometry was applied to quantify fentanyl and norfentanyl.

RESULTS

Ten patients were included in the study (8 men, 2 women). Fentanyl patches with delivery rates of 12-150μg/h were applied. Antemortem fentanyl levels in EDTA samples varied between 0.19 and 4.64μg/L. At 6 to 8hpm, blood concentrations of fentanyl were already significantly (p=0.05) higher in postmortem samples compared to the paired antemortem reference. On average, the antemortem concentration (range: 0.19-4.64μg/L) increased 3-fold within 6-8hpm (range: 0.4-14.9μg/L), and 5.5-fold within 24hpm (range: 0.39-21.88μg/L). Norfentanyl concentrations increased significantly (p=0.01) within 6-8hpm, too. In half of the patients, norfentanyl concentrations were below fentanyl concentrations, antemortem as well as postmortem.

CONCLUSION

Postmortem fentanyl concentrations increased quickly. As early as 6-8h after death, postmortem concentrations differ significantly from antemortem ones. Our results strongly indicate that postmortem blood concentrations of fentanyl after transdermal application should be interpreted carefully.

Monoclonal Antibodies for Combating Synthetic Opioid Intoxication

Opioid abuse in the United States has been declared a national crisis and is exacerbated by an inexpensive, readily available, and illicit supply of synthetic opioids. Specifically, fentanyl and related analogues such as carfentanil pose a significant danger to opioid users due to their high potency and rapid acting depression of respiration. In recent years these synthetic opioids have become the number one cause of drug-related deaths. In our research efforts to combat the public health threat posed by synthetic opioids, we have developed monoclonal antibodies (mAbs) against the fentanyl class of drugs. The mAbs were generated in hybridomas derived from mice vaccinated with a fentanyl conjugate vaccine. Guided by a surface plasmon resonance (SPR) binding assay, we selected six hybridomas that produced mAbs with 10^-11 M binding affinity for fentanyl, yet broad cross-reactivity with related fentanyl analogues. In mouse antinociception models, our lead mAb (6A4) could blunt the effects of both fentanyl and carfentanil in a dose-responsive manner. Additionally, mice pretreated with 6A4 displayed enhanced survival when subjected to fentanyl above LD₅₀ doses. Pharmacokinetic analysis revealed that the antibody sequesters large amounts of these drugs in the blood, thus reducing drug biodistribution to the brain and other tissue. Lastly, the 6A4 mAb could effectively reverse fentanyl/carfentanil-induced antinociception comparable to the opioid antagonist naloxone, the standard of care drug for treating opioid overdose. While naloxone is known for its short half-life, we found the half-life of 6A4 to be approximately 6 days in mice, thus monoclonal antibodies could theoretically be useful in preventing renarcotization events in which opioid intoxication recurs following quick metabolism of naloxone. Our results as a whole demonstrate that monoclonal antibodies could be a desirable treatment modality for synthetic opioid overdose and possibly opioid use disorder.

Pharmacokinetics of Fentanyl and Its Derivatives in Children: A Comprehensive Review

Fentanyl and its derivatives sufentanil, alfentanil, and remifentanil are potent opioids. A comprehensive review of the use of fentanyl and its derivatives in the pediatric population was performed using the National Library of Medicine PubMed. Studies were included if they contained original pharmacokinetic parameters or models using established routes of administration in patients younger than 18 years of age. Of 372 retrieved articles, 44 eligible pharmacokinetic studies contained data of 821 patients younger than 18 years of age, including more than 46 preterm infants, 64 full-term neonates, 115 infants/toddlers, 188 children, and 28 adolescents. Underlying diagnoses included congenital heart and pulmonary disease and abdominal disorders. Routes of drug administration were intravenous, epidural, oral-transmucosal, intranasal, and transdermal. Despite extensive use in daily clinical practice, few studies have been performed. Preterm and term infants have lower clearance and protein binding. Pharmacokinetics was not altered by chronic renal or hepatic disease. Analyses of the pooled individual patients' data revealed that clearance maturation relating to body weight could be best described by the Hill function for sufentanil (R ² = 0.71, B _max 876 mL/min, K ₅₀ 16.3 kg) and alfentanil (R ² = 0.70, B _{max (fixed)} 420 mL/min, K ₅₀ 28 kg). The allometric exponent for estimation of clearance of sufentanil was 0.99 and 0.75 for alfentanil clearance. Maturation of remifentanil clearance was described by linear regression to bodyweight (R ² = 0.69). The allometric exponent for estimation of remifentanil clearance was 0.76. For fentanyl, linear regression showed only a weak correlation between clearance and bodyweight in preterm and term neonates (R ² = 0.22) owing to a lack of data in older age groups. A large heterogeneity regarding study design, clinical setting, drug administration, laboratory assays, and pharmacokinetic estimation was observed between studies introducing bias into the analyses performed in this review. A limitation of this review is that pharmacokinetic data, based on different modes of administration, dosing schemes, and parameter estimation methods, were combined.

Correction to: Pharmacokinetics of Fentanyl and Its Derivatives in Children: A Comprehensive Review

Fentanyl and its derivatives sufentanil, alfentanil, and remifentanil are potent opioids. A comprehensive review of the use of fentanyl and its derivatives in the pediatric population was performed using the National Library of Medicine PubMed. Studies were included if they contained original pharmacokinetic parameters or models using established routes of administration in patients younger than 18 years of age. Of 372 retrieved articles, 44 eligible pharmacokinetic studies contained data of 821 patients younger than 18 years of age, including more than 46 preterm infants, 64 full-term neonates, 115 infants/toddlers, 188 children, and 28 adolescents. Underlying diagnoses included congenital heart and pulmonary disease and abdominal disorders. Routes of drug administration were intravenous, epidural, oral-transmucosal, intranasal, and transdermal. Despite extensive use in daily clinical practice, few studies have been performed. Preterm and term infants have lower clearance and protein binding. Pharmacokinetics was not altered by chronic renal or hepatic disease. Analyses of the pooled individual patients' data revealed that clearance maturation relating to body weight could be best described by the Hill function for sufentanil (R ² = 0.71, B _max 876 mL/min, K ₅₀ 16.3 kg) and alfentanil (R ² = 0.70, B _{max (fixed)} 420 mL/min, K ₅₀ 28 kg). The allometric exponent for estimation of clearance of sufentanil was 0.99 and 0.75 for alfentanil clearance. Maturation of remifentanil clearance was described by linear regression to bodyweight (R ² = 0.69). The allometric exponent for estimation of remifentanil clearance was 0.76. For fentanyl, linear regression showed only a weak correlation between clearance and bodyweight in preterm and term neonates (R ² = 0.22) owing to a lack of data in older age groups. A large heterogeneity regarding study design, clinical setting, drug administration, laboratory assays, and pharmacokinetic estimation was observed between studies introducing bias into the analyses performed in this review. A limitation of this review is that pharmacokinetic data, based on different modes of administration, dosing schemes, and parameter estimation methods, were combined.

Effect of Modulated Electrohyperthermia on the Pharmacokinetics of Oral Transmucosal Fentanyl Citrate in Healthy Volunteers

PURPOSE

This study aimed to determine whether changes occur in fentanyl absorption and disposition when administered in conjunction with modulated electrohyperthermia (mEHT) treatment.

METHODS

A randomized, single-dose, crossover, open-label study was used to investigate the effect of mEHT on the pharmacokinetic properties of fentanyl in 12 healthy volunteers. The 12 healthy volunteers were each administered a single dose of oral transmucosal fentanyl citrate (OTFC) or a single dose of OTFC with mEHT. mEHT was performed on the abdomen for 1 hour. Blood samples were collected for 24 hours after dosing. The temperature of the abdominal skin surface was assessed before dosing and at 10, 20, and 60 minutes after dosing.

FINDINGS

Geometric mean ratios (ratio of fentanyl with mEHT to fentanyl alone) for the C_max and AUC_0-last were 1.20 (90% CI, 1.09-1.32) and 1.15 (90% CI, 0.99-1.33), respectively. The mean temperature of the abdominal skin surface increased by approximately 4°C.

IMPLICATIONS

There was an increase in the overall exposure to the drug without implications of any clinical significance. OTFC can be administered without limitations in combination with mEHT, and it is not necessary to modify the dosing regimen. cris.nih.go,kr Identifier: KCT0001286.

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.

[Anesthesia and analgesia in the lactation period. Criteria for drug selection]

There is no sound information concerning the safe and correct use of analgesics and anesthetics during the lactation period based on studies with a large sample size. Available information is limited to case studies and small sample observations. As a result, information given by the drug manufacturers about the use of drugs during the lactation period is often restrictive or contains contraindications for the lactation period. Although some drugs are not officially licensed for use during lactation they need to be administered in daily (off-label) use. This review gives an overview about the recent knowledge and clinical experience concerning the perioperative use of anesthetics and analgesics during breast feeding.

Fentanyl for breakthrough pain: a systematic review

The purpose of this article is to systematically review the use of fentanyl as an analgesic for breakthrough pain. This article found that the oral transmucosal fentanyl (OTFC) had a quicker onset to analgesia than oral immediate-release opioids. Intranasal fentanyl (INFS) had a quicker onset to analgesia than buccal tablets, which in turn had a quicker onset to analgesia than OTFC. Patient acceptance and global rating of efficacy were greater for INFS than for buccal fentanyl. OTFC and INFS have been used effectively to reduce acute pain in children who are opioid-naive. Abuse and addiction to OTFC, fentanyl buccal tablets and INFS was low, owing to patient selection.

Analgesia and sedation after pediatric cardiac surgery

In recent years, the importance of appropriate intra-operative anesthesia and analgesia during cardiac surgery has become recognized as a factor in postoperative recovery. This includes the early perioperative management of the neonate undergoing radical surgery and more recently the care surrounding fast-track and ultra fast-track surgery. However, outside these areas, relatively little attention has focused on postoperative sedation and analgesia within the pediatric intensive care unit (PICU). This reflects perceived priorities of the primary disease process over the supporting structure of PICU, with a generic approach to sedation and analgesia that can result in additional morbidities and delayed recovery. Management of the marginal patient requires optimisation of not only cardiac and other attendant pathophysiology, but also every aspect of supportive care. Individualized sedation and analgesia strategies, starting in the operating theater and continuing through to hospital discharge, need to be regarded as an important aspect of perioperative care, to speed the process of recovery.

Symptom management for the adult patient dying with advanced chronic kidney disease: a review of the literature and development of evidence-based guidelines by a United Kingdom Expert Consensus Group

Improvement in end-of-life-care is required for patients dying with chronic kidney disease (CKD). The UK government now recommends that tools such as the Liverpool Care Pathway for the Dying Patient (LCP) be used to enhance the care of those patients dying with CKD. The LCP was originally developed for patients dying with terminal cancer, however has been shown to be transferable to patients dying with heart failure or stroke. On this background, in 2005 a UK National Renal LCP Steering Group was formed. The aim was to determine whether or not the generic LCP was transferable to patients dying with CKD. An Expert Consensus sub-group was established to produce evidence-based prescribing guidelines to allow safe and effective symptom control for patients dying with renal failure. These guidelines were finalised by the Expert Consensus group in August 2007 and endorsed by the Department of Health in March 2008. A literature search on symptom control and end-of-life care in renal failure was performed. A summary of the evidence was presented at a National Steering Group meeting. Opinions were given and provisional guidelines discussed. A first draft was produced and individually reviewed by all members of the Expert Group. Following review, amendments were made and a second draft written. This was presented to the entire National Steering Group and again individual comments were taken into consideration. A third and fourth draft were written and individually reviewed, before the guidelines were finalised by the Expert Consensus group. Patients dying with advanced CKD suffer symptoms similar to patients dying of cancer. The Renal LCP prescribing guidelines aim to control the same symptoms as the generic LCP: pain, dyspnoea, terminal restlessness and agitation, nausea and respiratory tract secretions. The evidence for the production of the guidelines is discussed and how a consensus was reached. A summary of the guidelines is given and the complete guidelines document is available via the Marie Curie Palliative Care Institute, Liverpool website.

Effect of voriconazole and fluconazole on the pharmacokinetics of intravenous fentanyl

OBJECTIVE

Fentanyl is a widely used opioid analgesic, which is extensively metabolized by hepatic cytochrome P450 (CYP) 3A. Recent reports suggest that concomitant administration of CYP3A inhibitors with fentanyl may lead to dangerous drug interactions.

METHODS

The potential interactions of fentanyl with triazole antifungal agents voriconazole and fluconazole were studied in a randomized crossover study in three phases. Twelve healthy volunteers were given 5 microg/kg of intravenous fentanyl without pretreatment (control), after oral voriconazole (400 mg twice on the first day and 200 mg twice on the second day), or after oral fluconazole (400 mg once on the first day and 200 mg once on the second day). Plasma concentrations of fentanyl, norfentanyl, voriconazole, and fluconazole were determined up to 24 h. Pharmacokinetic parameters were calculated using compartmental methods.

RESULTS

The mean plasma clearance of intravenous fentanyl was decreased by 23% (range -22 to 48%; p < 0.05) and 16% (-34 to 53%; p < 0.05) after voriconazole and fluconazole administration, respectively. Voriconazole increased the area under the fentanyl plasma concentration-time curve by 1.4-fold (p < 0.05). The initial plasma concentrations and volume of distribution of fentanyl did not differ significantly between phases.

CONCLUSION

Both voriconazole and fluconazole delay the elimination of fentanyl significantly. Caution should be exercised, especially in patients who are given voriconazole or fluconazole during long-lasting fentanyl treatment, because insidiously elevated fentanyl concentration may lead to respiratory depression.

Influence of CYP3A5 genotype on the pharmacokinetics and pharmacodynamics of the cytochrome P4503A probes alfentanil and midazolam

The hepatic and first-pass cytochrome P4503A (CYP3A) probe alfentanil (ALF) is also metabolized in vitro by CYP3A5. Human hepatic microsomal ALF metabolism is higher in livers with at least one CYP3A5*1 allele and higher CYP3A5 protein content, compared with CYP3A5*3 homozygotes with little CYP3A5. The influence of CYP3A5 genotype on ALF pharmacokinetics and pharmacodynamics was studied, and compared to midazolam (MDZ), another CYP3A probe. Healthy volunteers (58 men, 41 women) were genotyped for CYP3A5 *1, *3, *6, and *7 alleles. They received intravenous MDZ then ALF, and oral MDZ and ALF the next day. Plasma MDZ and ALF concentrations were determined by mass spectrometry. Dark-adapted pupil diameters were determined coincident with blood sampling. In CYP3A5(*)3/(*)3 (n=62), (*)1/(*)3 (n=28), and (*)1/(*)1 (n=8) genotypes, systemic clearances of ALF were 4.6+/-1.8, 4.8+/-1.7, and 3.9+/-1.7 ml/kg/min and those of MDZ were 7.8+/-2.3, 7.7+/-2.3, and 6.0+/-1.4 ml/kg/min, respectively (not significant), and apparent oral clearances were 11.8+/-7.2, 13.3+/-6.1, and 12.6+/-8.2 ml/kg/min for ALF and 35.2+/-19.0, 36.4+/-15.7, and 29.4+/-9.3 ml/kg/min for MDZ (not significant). Clearances were not different between African Americans (n=25) and Whites (n=68), or between CYP3A5 genotypes within African Americans. ALF pharmacodynamics was not different between CYP3A5 genotypes. There was consistent concordance between ALF and MDZ, in clearances and extraction ratios. Thus, in a relatively large cohort of healthy subjects with constitutive CYP3A activity, CYP3A5 genotype had no effect on the systemic or apparent oral clearances, or pharmacodynamics, of the CYP3A probes ALF and MDZ, despite affecting their hepatic microsomal metabolism.

Alfentanil-induced miosis as a surrogate measure of alfentanil pharmacokinetics in patients with mild and moderate liver cirrhosis

OBJECTIVES

(i) To evaluate the pupillary response to alfentanil as a surrogate measure of alfentanil pharmacokinetics in cirrhotic patients and to compare the data observed in cirrhotic patients with those found in healthy volunteers (historical control group); and (ii) to compare this test with other liver function tests in cirrhotic patients.

METHODS

Six patients with mild cirrhosis (Child-Pugh grade A) and six patients with moderate cirrhosis (Child-Pugh grade B) were studied after a single 15 microg/kg bolus of alfentanil. Alfentanil plasma concentrations were measured by liquid chromatography-tandem mass spectrometry, and pupillary responses were measured with a Pupilscan II pupillometer. Alfentanil pharmacokinetics (plasma concentration, area under the plasma concentration-time curve from time zero to infinity [AUC(infinity(p))] and from time zero to 2 hours [AUC(2(p))], apparent volume of distribution at steady state, clearance and terminal elimination half-life [t((1/2)(p))]) and miosis pseudo-kinetic parameters [AUC(infinity)((miosis)), AUC(2)((miosis)), t((1/2))((miosis))] were determined using a noncompartmental analysis method. In six patients (three Child-Pugh grade A and three Child-Pugh grade B), antipyrine (measure of liver intrinsic activity) and D-sorbitol (measure of liver blood flow) tests were performed.

RESULTS

A significant correlation was found between the alfentanil AUC(infinity(p)) and AUC(infinity)((miosis)) (r = 0.6, p < 0.05) in cirrhotic patients. This correlation was even more significant if AUC determinations were limited to the first 2 hours after alfentanil administration (r = 0.9, p < 0.01). Statistically significant differences in pharmacokinetics and miosis pseudo-kinetic parameters were observed between cirrhotic patients and healthy volunteers from our previous experiment (historical control group). The correlations were significant between alfentanil clearance and antipyrine clearance (n = 6, r = 0.9, p < 0.05), alfentanil clearance and steady-state hepatic blood clearance [CL(H(b))] measured by the D-sorbitol test (n = 6, r = 0.9, p < 0.05).

CONCLUSION

Alfentanil pharmacokinetic parameters were correlated with miosis pseudo-kinetic parameters in cirrhotic patients. There was a significant decrease in pharmacokinetics and miosis pseudo-kinetics in cirrhotic patients compared with volunteers from the historical control group. Alfentanil-induced miosis has the advantage of being noninvasive and can be limited to miosis measurements during the first 2 hours after alfentanil administration in cirrhotic patients. We thus propose to substitute the AUC(2(miosis)) for alfentanil pharmacokinetics in cirrhosis.

Fentanyl clearance and volume of distribution are increased in patients with major burns

This study examined the pharmacokinetics of fentanyl in burned patients during the hyperdynamic phase. Twenty adults, aged 37 +/- 2 years (mean +/- SE), with 49 +/- 3% total body surface area burn, were studied at 17 +/- 2 days after the injury and compared to demographically matched controls. After a 200-microg IV bolus of fentanyl, blood samples (n = 20) were collected for 4.5 hours. Concentration-time curves were fitted to a 2-compartment model. Burned patients had a higher cardiac index. Median fentanyl clearance (CL, 21.0 vs 29.4 mL/kg/min), central compartment volume (V(1), 0.37 vs 0.61 L/kg), and total volume of distribution (V(area), 3.6 vs 5.8 L/kg) were higher in burned patients. Cardiac index was unrelated to CL. The increased V(1) and V(area) are likely due to large intravenous fluid replacement and tissue edema. Higher CL and larger V(1) and V(area) leading to a lower fentanyl plasma concentration may partially explain the increased opiate requirement previously observed after burn injury.

Fentanyl HCl patient-controlled iontophoretic transdermal system for the management of acute postoperative pain

OBJECTIVE

To summarize the pharmaceutics, pharmacokinetics, development, and clinical application of IONSYS, the fentanyl HCl patient-controlled iontophoretic transdermal system for the management of acute postoperative pain.

DATA SOURCES

Clinical literature including both primary sources and review articles was accessed through a search of the MEDLINE databases (1980-October 2006). Key search terms included cutaneous analgesia, fentanyl, IONSYS, opioid, postoperative pain, and patient-controlled analgesia (PCA). Additional clinical trial and drug data were supplied by the manufacturer, the ALZA Corporation.

STUDY SELECTION AND DATA EXTRACTION

Review articles, abstracts, and clinical studies related to patient-controlled iontophoretic transdermal fentanyl and postoperative pain management were analyzed. An evaluation of the research exploring IONSYS for the management of acute postoperative pain was conducted. Relevant information was then selected and is provided in this article.

DATA SYNTHESIS

IONSYS is the first iontophoretic transdermal drug delivery system that utilizes low-level electrical energy to actively transport ionized fentanyl HCl through intact skin. Research has revealed that use of IONSYS for patients with acute postoperative pain is safe, effective, and well tolerated. Phase I-III trials have demonstrated an appropriate dosing range leading to effective analgesia, with minimal adverse effects. The analgesia provided by this system was found to be superior to that of analgesia placebo and equivalent to that of an intravenous morphine PCA.

CONCLUSIONS

Data from clinical trials indicated that IONSYS is successful in controlling acute postoperative pain that circumvents the limitations of intravenous patient-controlled analgesia. The use of this system may serve as an alternative modality for the management of acute pain without increasing such adverse effects as bleeding, intravenous catheter infiltration, or manual pump malfunction.

Alfentanil-induced miosis clearance as a liver CYP3A4 and 3A5 activity measure in healthy volunteers: improvement of experimental conditions

The aims of this study were to demonstrate the correlation between alfentanil-induced miosis evaluation and alfentanil pharmacokinetics (PK) as a CYP3A4 and 3A5 activity probe in volunteers and to explain the variability in pupilar response and in alfentanil PK. In ambient light, the miosis kinetic parameters were significantly correlated with PK (CLs: r = 0.9, P = .00; AUCs: r = 0.8, P = .01). In dark, a similar correlation was observed between miosis and alfentanil clearances (r = 0.85, P = .03). In 6 volunteers, the sigmoid E(max) model was applicable (average E(max) = 2.5 +/- 0.7 mm, gamma = 2.5 +/- 1.6 and EC(50) = 76.8 +/- 22.3 ng/mL), and in 3, the simple E(max) model was applicable (average E(max) = 2.8 +/- 0.3 mm and EC(50) = 19.9 +/- 8.5 ng/mL). There was a large interindividual variability in PK parameters (coefficient of variation = 19.7%-31.2%). Free drug fraction concentrations were negatively correlated with plasma alpha(1)-AGP (r = -0.9, P = .04) and albumin levels (r = -0.94, P = .02). Alfentanil-induced miosis clearance as a noninvasive CYP3A4 and 3A5 activity measure can be done in both ambient and dark conditions. Drug free fraction may be responsible for large intersubject variability in alfentanil PK.

The effect of opioid analgesia on exercise test performance in chronic low back pain

The effect of opioid analgesia on tests of muscular function in chronic low back pain (CLBP) is unknown. Twenty-eight subjects with CLBP of at least moderate intensity performed the Sorensen isokinetic exercise test once after receiving 1 microg/kg fentanyl intravenously and once after placebo in a randomized-order double-blind crossover design. Naloxone 3 microg/kg was administered after the fentanyl phase. Fentanyl reduced mean+/-SD pain from 4.0+/-2.1 to 3.1+/-2.2 on a 0-10 verbal rating scale (P<0.05). Mean+/-SD Sorensen test performance was 77+/-49 s in the fentanyl arm and 60+/-42 s in the placebo arm. This represents an increased performance with fentanyl of 28% (P<0.001). We conclude that in addition to relieving pain in CLBP, the administration of 1 microg/kg fentanyl is associated with an improvement in lumbar exercise test performance. We presume that the pain relief resulted in increased test performance. Our result is at odds with those of randomized trials which have failed to demonstrate increased function following the treatment of pain with opioid analgesics. This highlights the complexity of the interaction between pain, analgesia and changes in function.

Efficacy and safety of continuous intravenous infusion of remifentanil in preterm infants undergoing laser therapy in retinopathy of prematurity: clinical experience

BACKGROUND

Preterm infants often require surgery. As experimental evidence suggests that premature infants may experience pain and this could even result in fatal complications, the anaesthesiologist must face problems related to lowbirth weight, high risk of hypothermia, concomitant pulmonary disease and metabolic and receptor immaturity. Recently remifentanil has been considered an optimal analgesic drug in a preterm infant undergoing mechanical ventilation and frequent surgical manoeuvres, but no clinical studies have been reported in the literature. The aim of our study was to evaluate the efficacy of a continuous intravenous infusion of remifentanil in premature infants undergoing laser therapy for retinopathy of prematurity (ROP).

METHODS

Six premature infants with ROP were scheduled for laser therapy. The procedure was performed in the neonatal intensive care unit. Transcutaneous carbon dioxide, pulse oximetry, respiratory rate, ECG and noninvasive blood pressure were continuously monitored. Infusion of remifentanil started with a dose of 0.75-1 microg x kg-1x min-1, 1 h before surgery. A midazolam bolus dose (0.20 mg x kg-1) was administered and the remifentanil infusion was increased to 3-5 microg x kg-1x min-1 taking into account haemodynamic and respiratory changes or spontaneous movements.

RESULTS

Increased dosage was necessary only for 10 min during the procedure. No changes in temperature and ventilatory settings were observed and after 2 h from the surgical procedure the preterm infants were back to their preoperative status.

CONCLUSIONS

A continuous infusion of remifentanil allowed optimal control of surgical stress and a return to preoperative status and ventilatory settings without side-effects.

Human variability in CYP3A4 metabolism and CYP3A4-related uncertainty factors for risk assessment

CYP3A4 constitutes the major liver cytochrome P450 isoenzyme and is responsible for the oxidation of more than 50% of all known drugs. Human variability in kinetics for this pathway has been quantified using a database of 15 compounds metabolised extensively (>60%) by this CYP isoform in order to develop CYP3A4-related uncertainty factors for the risk assessment of environmental contaminants handled via this route. Data were analysed from published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and other subgroups using parameters relating primarily to chronic exposure [metabolic and total clearances, area under the plasma concentration-time curve (AUC)] and acute exposure (Cmax). Interindividual variability in kinetics was greater for the oral route (46%, 12 compounds) than for the intravenous route (32%, 14 compounds). The physiological and molecular basis for the difference between these two routes of exposure is discussed. In relation to the uncertainty factors used for risk assessment, the default kinetic factor of 3.16 would be adequate for adults, whereas a CYP3A4-related factor of 12 would be required to cover up to 99% of neonates, which have lower CYP3A4 activity.

Quantitative analysis of fentanyl in rat plasma by gas chromatography with nitrogen-phosphorus detection

A sensitive assay method was developed to determine fentanyl, an opiate agonist, in rat plasma by gas chromatography with nitrogen-phosphorus detection. For the pretreatment of plasma samples, sodium hydroxide was added to denature protein and n-butyl chloride was used to extract fentanyl. The calibration curve was linear within the concentration range 0.5 to 50 ng/ml (r=0.9997). The limit of detection was 0.1 ng/ml, and 0.5 ng/ml could be quantified with acceptable precision. Furthermore, fentanyl could be determined in only 200 microl of rat plasma. The method has been successfully applied to an intramuscular pharmacokinetic study at a dose of 10 microg/kg. Therefore, the current method is a valuable analytical tool for investigating the pharmacokinetics of fentanyl at low clinical doses.

Target-controlled infusion systems: role in anaesthesia and analgesia

Drug delivery by target-controlled infusion (TCI) allows automatic adjustments of the infusion rate of a drug to maintain a desired target concentration. Since drug effect is more closely related to blood concentration than to infusion rate, drug delivery via TCI is capable of creating stable blood concentrations of intravenous anaesthetics and analgesics. In this article the concept and history of TCI are described. The rational administration of TCI requires an appropriate pharmacokinetic data set and knowledge of the concentration-effect relationship; therefore, general pharmacokinetic and pharmacodynamic aspects of intravenous anaesthetics and analgesics are also addressed. Intraoperative investigations have demonstrated that TCI drug delivery allows rapid titration to a desired effect. The use of TCI for postoperative analgesia is still experimental, but TCI can, in part, overcome the disadvantages associated with continuous infusions and patient-controlled analgesia regimens in the postoperative period. Although TCI is capable of creating stable blood concentrations, when the target concentration is changed the resulting effect correlates better with a theoretical effect site concentration. The efficacy of TCI systems that can perform effect-site steering are still to be explored.

Total intravenous anesthesia in greyhounds: pharmacokinetics of propofol and fentanyl--a preliminary study

OBJECTIVE

To evaluate concomitant propofol and fentanyl infusions as an anesthetic regime, in Greyhounds.

ANIMALS

Eight clinically normal Greyhounds (four male, four female) weighing 25.58 +/- 3.38 kg.

DESIGN

Prospective experimental study.

METHODS

Dogs were premedicated with acepromazine (0.05 mg/kg) by intramuscular (i.m.) injection. Forty five minutes later anesthesia was induced with a bolus of propofol (4 mg/kg) by intravenous (i.v.) injection and a propofol infusion was begun (time = 0). Five minutes after induction of anesthesia, fentanyl (2 microg/kg) and atropine (40 microg/kg) were administered i.v. and a fentanyl infusion begun. Propofol infusion (0.2 to 0.4 mg/kg/min) lasted for 90 minutes and fentanyl infusion (0.1 to 0.5 microg/kg/min) for 70 minutes. Heart rate, blood pressure, respiratory rate, end-tidal carbon dioxide, body temperature, and depth of anesthesia were recorded. The quality of anesthesia, times to return of spontaneous ventilation, extubation, head lift, and standing were also recorded. Blood samples were collected for propofol and fentanyl analysis at varying times before, during and after anesthesia.

RESULTS

Mean heart rate of all dogs varied from 52 to 140 beats/min during the infusion. During the same time period, mean blood pressure ranged from 69 to 100 mm Hg. On clinical assessment, all dogs appeared to be in light surgical anesthesia. Mean times (+/- SEM), after termination of the propofol infusion, to return of spontaneous ventilation, extubation, head lift and standing for all dogs were 26 +/- 7, 30 +/- 7, 59 +/- 12, and 105 +/- 13 minutes, respectively. Five out of eight dogs either whined or paddled their forelimbs in recovery. Whole blood concentration of propofol for all eight dogs ranged from 1.21 to 6.77 microg/mL during the infusion period. Mean residence time (MRTinf) for propofol was 104.7 +/- 6.0 minutes, mean body clearance (Clb) was 53.35 +/- 0.005 mL/kg/min, and volume of distribution at steady state (Vdss) was 3.27 +/- 0.49 L/kg. Plasma concentration of fentanyl for seven dogs during the infusion varied from 1.22 to 4.54 ng/mL. Spontaneous ventilation returned when plasma fentanyl levels were >0.77 and <1.17 ng/mL. MRTinf for fentanyl was 111.3 +/- 5.7 minutes. Mean body clearance was 29.1 +/- 2.2 mL/kg/min and Vdss was 2.21 +/- 0.19 L/kg.

CONCLUSION AND CLINICAL RELEVANCE

In Greyhounds which were not undergoing any surgical stimulation, total intravenous anesthesia maintained with propofol and fentanyl infusions induced satisfactory anesthesia, provided atropine was given to counteract bradycardia. Despite some unsatisfactory recoveries the technique is worth investigating further for clinical cases, in this breed and in mixed breed dogs.

A comparison of subcutaneous morphine and fentanyl in hospice cancer patients

This study compares subcutaneous (s.c.) morphine and fentanyl with respect to pain control and side effects using a 6-day randomized, double-blind, cross-over design. Results were obtained from 23 patients (12 males and 11 females: mean age of 70.5 years) who could tolerate morphine. Thirteen patients were randomized to receive morphine for the first 3 days followed by fentanyl; 10 received fentanyl first followed by morphine. There were no significant differences in the scores for pain between the two drugs, suggesting that fentanyl is equally efficacious and the conversion ratio of morphine 10 mg: fentanyl 150 micrograms is appropriate. Patients had more frequent bowel movements during days 4-6 while on the fentanyl arm [t-test, df (22), P = 0.015]. Other measures for nausea, delirium, and cognitive function showed no differences between the two drugs. This study highlights the need to further assess the role of various opioids in hospice patients, and emphasizes the requirement for sensitive and simple cognitive tests in this population.

Pharmacokinetics of opioids in liver disease

The liver is the major site of biotransformation for most opioids. Thus, the disposition of these drugs may be affected in patients with liver insufficiency. The major metabolic pathway for most opioids is oxidation. The exceptions are morphine and buprenorphine, which primarily undergo glucuronidation, and remifentanil, which is cleared by ester hydrolysis. Oxidation of opioids is reduced in patients with hepatic cirrhosis, resulting in decreased drug clearance [for pethidine (meperidine), dextropropoxyphene, pentazocine, tramadol and alfentanil] and/or increased oral bioavailability caused by a reduced first-pass metabolism (for pethidine, dextropropoxyphene, pentazocine and dihydrocodeine). Although glucuronidation is thought to be less affected in liver cirrhosis, and clearance of morphine was found to be decreased and oral bioavailability increased. The consequence of reduced drug metabolism is the risk of accumulation in the body, especially with repeated administration. Lower doses or longer administration intervals should be used to remedy this risk. Special risks are known for pethidine, with the potential for the accumulation of norpethidine, a metabolite that can cause seizures, and for dextropropoxyphene, for which several cases of hepatotoxicity have been reported. On the other hand, the analgesic activity of codeine and tilidine depends on transformation into the active metabolites, morphine and nortilidine, respectively. If metabolism is decreased in patients with chronic liver disease, the analgesic action of these drugs may be compromised. Finally, the disposition of a few opioids, such as fentanyl, sufentanil and remifentanil, appears to be unaffected in liver disease.

Remifentanil, fentanyl, and alfentanil have no influence on the respiratory burst of human neutrophils in vitro

BACKGROUND

Anaesthetic agents inhibit certain functions of human neutrophils. The respiratory burst (RB) enzyme in the plasma membrane of neutrophils leads to the production of superoxide anion. The oxygen radicals are responsible for killing phagocytised micro-organisms. We investigated the in vitro influence of remifentanil, fentanyl, and alfentanil on the respiratory burst of human neutrophils.

METHODS

For the flow-cytometric evaluation, leukocytes were obtained as supernatant following sedimentation and were incubated with the tested drugs. The concentrations in vitro were adjusted to conform to the plasma concentrations reported for anaesthesia and also to 10-fold higher concentrations. The RB was measured by intracellular oxidation of dihydrorhodamine to fluorescent rhodamine after induction of phorbol-myristate-acetate (PMA), Escherichia coli (E. coli) or priming by tumour necrosis factor alpha followed by stimulation of n-formyl-methionyl-leucyl-phenylalanine (TNF-alpha/FMLP). In order to exclude prestimulation of the neutrophil granulocytes, negative controls were carried out. Propidium iodide (PI) was added for viability discrimination immediately prior to flow cytometry measurement.

RESULTS

Regardless of the triggering agents chosen (PMA, E. coli, TNF-alpha/FMLP), remifentanil, fentanyl, and alfentanil had no significant effect on the neutrophils' respiratory burst even in concentrations which were higher than those encountered during in vivo conditions.

CONCLUSION

With respect to peri- and postoperative risk of infection, anaesthetics and analgetics with no inhibiting effect on neutrophil function should be used. These results show that remifentanil, fentanyl, and alfentanil do not influence the neutrophils' respiratory burst in vitro.

Possible involvement of multiple cytochrome P450S in fentanyl and sufentanil metabolism as opposed to alfentanil

Fentanyl, sufentanil, and alfentanil are commonly used as opioid analgesics. Alfentanil clearance has previously been shown to exhibit an important interindividual variability, which was not observed for fentanyl or sufentanil. Differences in pharmacokinetic parameters of alfentanil have previously been associated with the wide distribution of CYP3A4, the only known hepatic cytochrome P450 monooxygenase (CYP) involved in the conversion of alfentanil to noralfentanil. Little is known about the involvement of CYP enzymes in the oxidative metabolism of fentanyl and sufentanil. Microsomes prepared from different human liver samples were compared for their abilities to metabolize fentanyl, sufentanil and alfentanil, and it was found that disappearance of the three substrates was well correlated with immunoreactive CYP3A4 contents but not with other CYPs, including CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2D6 and CYP2E1. Specific known inhibitors of CYP enzymes gave similar results, whereas the use of recombinant human CYP enzymes expressed in yeast provided information about the possible involvement of other CYPs than CYP3A4 in the biotransformation of fentanyl and sufentanil. The possible in vivo interaction of fentanyl and sufentanil with other drugs catalyzed by CYP3A4 is also discussed.

Pharmacokinetics of opioids in renal dysfunction

Patients with renal insufficiency commonly require the administration of an opioid analgesic to provide adequate pain relief. The handling of morphine, pethidine (meperidine) and dextropropoxyphene in patients with renal insufficiency is complicated by the potential accumulation of metabolites. While morphine itself remains largely unaffected by renal failure, accumulation, as denoted by an increase in both mean peak concentrations and the area under the concentration-time curve, of both the active metabolite (morphine-6-glucuronide) and the principal metabolite (morphine-3-glucuronide, thought to possess opiate antagonist properties) have been reported. The increased elimination half-lives of the toxic metabolites norpethidine and norpropoxyphene in patients with poor renal function administered pethidine and dextropropoxyphene, respectively, makes their routine use ill advised. Case reports of prolonged narcosis associated with the use of both codeine and dihydrocodeine in patients with renal insufficiency call for care to be used when prescribing these agents under such conditions. Although the pharmacokinetics of buprenorphine, alfentanil, sufentanil and remifentanil change little in patients with renal failure, the continuous administration of fentanyl can lead to prolonged sedation.

Epidural vs. intravenous infusion of alfentanil in the management of postoperative pain following laparotomies

BACKGROUND

This study was designed to compare the efficacy of epidural vs. intravenous administration of alfentanil for treatment of postoperative pain.

METHODS

Twenty patients were randomly allocated to one of the two study groups to receive either an epidural bolus dose (0.75 mg) followed by an epidural infusion (0.36 mg/h) (EPI group) or an intravenous infusion (0.36 mg/h) of alfentanil (IV group) for 24 h. These dose regimens were chosen such that equivalent and subanalgesic plasma concentrations of alfentanil were obtained. PCA-morphine was available to both groups. Morphine consumption, pain scores measured on a Visual Analogue Scale (VAS) and the number of demands were used as variables to evaluate the efficacy of the postoperative analgesic therapy. In addition, plasma concentrations of alfentanil were measured.

RESULTS

The mean plasma concentrations of alfentanil were similar and < 20 ng/ml in both groups. Total morphine consumption (EPI: 40 mg, i.v.: 43 mg), pain scores (time when the VAS-score > 3.0: EPI: median 215 min; i.v.: median 215 min) and number of valid demands (EPI: median 25; i.v.: median 34) did not differ between the groups.

CONCLUSION

Compared to intravenous infusion of alfentanil epidural infusion resulting in the same plasma concentrations is not more effective in relieving postoperative pain. In view of this observation we were not able to demonstrate a spinal mechanism of alfentanil.