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.

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.

Analysis of fentanyl pharmacokinetics, and its sedative effects and tolerance in critically ill children

INTRODUCTION

Fentanyl pharmacokinetic and pharmacodynamic data are limited in mechanically ventilated children. This study aimed to assess the fentanyl pharmacokinetics (PK), the sedation outcome, and the development of tolerance in children receiving fentanyl continuous infusion.

METHODS

This study included children admitted to the pediatric or cardiovascular intensive care unit between January 1 and October 31, 2016, who were >30 days to <18 years of age, receiving ventilatory support via endotracheal tube or tracheostomy, and receiving a fentanyl infusion. Population PK analysis was performed using a nonlinear mixed-effects model. The relationship between initial sedation outcome using State Behavioral Scale (SBS) and fentanyl exposure was assessed, and the observations consistent with tolerance were described.

RESULTS

Seventeen children, with a median age of 0.83 years (range: 0.1-12) and weight of 8.7 kg (range: 3.4-52), were included. The fentanyl PK was adequately described by a weight-based allometry model with the power of 0.75 for clearance (CL=89.8 L/hr/70 kg) and distributional CL, and 1 for volumes of distribution. In infants <6.6 months, age was an additional factor for CL (31.4 L/h/70 kg) to account for age-related maturation. Seven of twelve nonparalyzed patients achieved goal sedation, defined as >80% of SBS scores ≤0 per 24 h, on the first day of fentanyl infusion with a median plasma concentration of 1.29 ng/ml (interquartile range: 0.78-2.05). Eight of the nine tolerant patients developed tolerance within a day of reaching goal sedation.

CONCLUSION

Different weight-based fentanyl dosing rates may be required for infants and children of different ages to achieve similar plasma concentrations. Using SBS scores may guide the dosing titration of fentanyl that resulted in plasma concentrations within the therapeutic range of 1-3 ng/ml. For those who developed tolerance to fentanyl and/or a sedative, it was noted one day after goal sedation was achieved.

Tolerance to Opioid-Induced Respiratory Depression in Chronic High-Dose Opioid Users: A Model-Based Comparison With Opioid-Naïve Individuals

Chronic opioid consumption is associated with addiction, physical dependence, and tolerance. Tolerance results in dose escalation to maintain the desired opioid effect. Intake of high-dose or potent opioids may cause life-threatening respiratory depression, an effect that may be reduced by tolerance. We performed a pharmacokinetic-pharmacodynamic analysis of the respiratory effects of fentanyl in chronic opioid users and opioid-naïve subjects to quantify tolerance to respiratory depression. Fourteen opioid-naïve individuals and eight chronic opioid users received escalating doses of intravenous fentanyl (opioid-naïve subjects: 75-350 µg/70 kg; chronic users: 250-700 µg/70 kg). Isohypercapnic ventilation was measured and the fentanyl plasma concentration-ventilation data were analyzed using nonlinear mixed-effects modeling. Apneic events occurred in opioid-naïve subjects after a cumulative fentanyl dose (per 70 kg) of 225 (n = 3) and 475 µg (n = 6), and in 7 chronic opioid users after a cumulative dose of 600 (n = 2), 1,100 (n = 2), and 1,800 µg (n = 3). The time course of fentanyl's respiratory depressant effect was characterized using a biophase equilibration model in combination with an inhibitory maximum effect (Emax ) model. Differences in tolerance between populations were successfully modeled. The effect-site concentration causing 50% ventilatory depression, was 0.42 ± 0.07 ng/mL in opioid-naïve subjects and 1.82 ± 0.39 ng/mL in chronic opioid users, indicative of a 4.3-fold sensitivity difference. Despite higher tolerance to fentanyl-induced respiratory depression, apnea still occurred in the opioid-tolerant population indicative of the potential danger of high-dose opioids in causing life-threatening respiratory depression in all individuals, opioid-naïve and opioid-tolerant.

The influence of cardiac output on propofol and fentanyl pharmacokinetics and pharmacodynamics in patients undergoing abdominal aortic surgery

Cardiac output (CO) is expected to affect elimination and distribution of highly extracted and perfusion rate-limited drugs. This work was undertaken to quantify the effect of CO measured by the pulse pressure method on pharmacokinetics and pharmacodynamics of propofol and fentanyl administrated during total intravenous anesthesia (TIVA). The data were obtained from 22 ASA III patients undergoing abdominal aortic surgery. Propofol was administered via target-controlled infusion system (Diprifusor) and fentanyl was administered at a dose of 2-3 µg/kg each time analgesia appeared to be inadequate. Hemodynamic measurements as well as bispectral index were monitored and recorded throughout the surgery. Data analysis was performed by using a non-linear mixed-effect population modeling (NONMEM 7.4 software). Three compartment models that incorporated blood flows as parameters were used to describe propofol and fentanyl pharmacokinetics. The delay of the anesthetic effect, with respect to plasma concentrations, was described using a biophase (effect) compartment. The bispectral index was linked to the propofol and fentanyl effect site concentrations through a synergistic Emax model. An empirical linear model was used to describe CO changes observed during the surgery. Cardiac output was identified as an important predictor of propofol and fentanyl pharmacokinetics. Consequently, it affected the depth of anesthesia and the recovery time after propofol-fentanyl TIVA infusion cessation. The model predicted (not observed) CO values correlated best with measured responses. Patients' age was identified as a covariate affecting the rate of CO changes during the anesthesia leading to age-related difference in individual patient's responses to both drugs.

Toxicokinetics and toxicodynamics of the fentanyl homologs cyclopropanoyl-1-benzyl-4´-fluoro-4-anilinopiperidine and furanoyl-1-benzyl-4-anilinopiperidine

The two fentanyl homologs cyclopropanoyl-1-benzyl-4´-fluoro-4-anilinopiperidine (4F-Cy-BAP) and furanoyl-1-benzyl-4-anilinopiperidine (Fu-BAP) have recently been seized as new psychoactive substances (NPS) on the drugs of abuse market. As their toxicokinetic and toxicodynamic characteristics are completely unknown, this study focused on elucidating their in vitro metabolic stability in pooled human liver S9 fraction (pHLS9), their qualitative in vitro (pHLS9), and in vivo (zebrafish larvae) metabolism, and their in vitro isozyme mapping using recombinant expressed isoenzymes. Their maximum-tolerated concentration (MTC) in zebrafish larvae was studied from 0.01 to 100 µM. Their µ-opioid receptor (MOR) activity was analyzed in engineered human embryonic kidney (HEK) 293 T cells. In total, seven phase I and one phase II metabolites of 4F-Cy-BAP and 15 phase I and four phase II metabolites of Fu-BAP were tentatively identified by means of liquid chromatography high-resolution tandem mass spectrometry, with the majority detected in zebrafish larvae. N-Dealkylation, N-deacylation, hydroxylation, and N-oxidation were the most abundant metabolic reactions and the corresponding metabolites are expected to be promising analytical targets for toxicological analysis. Isozyme mapping revealed the main involvement of CYP3A4 in the phase I metabolism of 4F-Cy-BAP and in terms of Fu-BAP additionally CYP2D6. Therefore, drug-drug interactions by CYP3A4 inhibition may cause elevated drug levels and unwanted adverse effects. MTC experiments revealed malformations and changes in the behavior of larvae after exposure to 100 µM Fu-BAP. Both substances were only able to produce a weak activation of MOR and although toxic effects based on MOR activation seem unlikely, activity at other receptors cannot be excluded.

Sex-by-formulation interaction in bioequivalence trials with transdermal patches

PURPOSE

The existence of a sex-by-formulation interaction in bioequivalence studies implies that the bioequivalence results (i.e., the test/reference ratio of the pharmacokinetic parameters) obtained in one sex are not similar to those obtained in the other sex. Therefore, results obtained in studies including only males may not be representative of the results obtained in females and vice versa. The best evidence of the existence of a sex-by-formulation interaction has been obtained from a study conducted with transdermal patches. This observation might be caused by the different characteristics of the skin of males and females. The purpose of this work is to investigate the existence of a sex-by-formulation interaction in all bioequivalence studies of transdermal patches submitted to the Spanish Agency for Medicines between 2010 and 2016.

METHODS

Only five different products (Buprenorphine-1, Fentantyl-1, Fentanyl-2, Rivastigmine-1 and Rivastigmine-2) that were submitted for registration included nine bioequivalence studies conducted in males and females. As single dose and multiple dose studies are required for registration of transdermal patches in the European Union, more than one study may be available to confirm the existence of a sex-by-formulation interaction.

RESULTS

A sex-by-formulation interaction is suggested in six out of 27 datasets (22%), corresponding to two products, and it is statistically significant in three of them (11%).

CONCLUSIONS

The sex-by-formulation interaction detected in some pharmacokinetic parameters of some studies is excluded when the study is repeated, which shows that these results are not reproducible. There is no evidence to require bioequivalence demonstration for transdermal patches in males and females separately.

Pharmacokinetics of Fentanyl Sublingual Spray in Opioid-Naïve Participants: Results of a Phase 1, Multiple Ascending Dose Study

Background and Objectives

Fentanyl sublingual spray may be a viable alternative to intravenous (IV) opioids for the treatment of acute pain. As patients with acute pain may include those who have limited prior exposure to opioids, this phase 1, open-label, randomized, multiple ascending-dose study was conducted to assess the pharmacokinetics, pharmacodynamics, safety, and tolerability of multiple doses of fentanyl sublingual spray in opioid-naïve participants. This article primarily reports the pharmacokinetics results.

Methods

Study drugs were administered in four dosing cohorts: every 0.5, 1, 2, or 4 h for a maximum of three doses per cohort. Eight fasted individuals per cohort were randomized to either fentanyl sublingual spray (100, 200, or 400 µg) or fentanyl citrate IV 50 µg (6:2 ratio). Blood samples were collected pre-dose through 24 h post first dose.

Results

A total of 98 healthy adults were enrolled and 96 completed the study. Mean plasma fentanyl concentrations increased with increasing doses of fentanyl sublingual spray administered every 0.5–4 h. With multiple doses, systemic exposure increased relative to the first dose; shorter dosing intervals resulted in higher concentrations. Analysis of dose proportionality suggested that systemic exposure increased in a linear but slightly greater than dose-proportional manner. Accumulation between the first and last doses of fentanyl sublingual spray was more pronounced with shorter dosing intervals.

Conclusion

Dose-dependent fentanyl pharmacokinetics following multiple doses of fentanyl sublingual spray were well characterized in an opioid-naïve population.

ClinicalTrials.gov identifier

NCT02641340.

Electronic supplementary material

The online version of this article (10.1007/s40261-018-0658-9) contains supplementary material, which is available to authorized users.

Postmortem analysis of three methoxyacetylfentanyl-related deaths in Denmark and in vitro metabolite profiling in pooled human hepatocytes

Methoxyacetylfentanyl belongs to the group of fentanyl analogues and has been associated with several deaths in recent years. We present three case reports of deceased individuals that tested positive for methoxyacetylfentanyl consumption, as well as in vitro and in vivo metabolite profiles. Methoxyacetylfentanyl was quantified by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) in femoral blood, as well as in urine and brain tissue when these were available. Metabolite profiling was performed by incubating methoxyacetylfentanyl with pooled human hepatocytes (pHH) in Leibovitz's L-15 medium supplemented with fetal bovine serum. Metabolites were identified in vivo and in vitro using UHPLC-high resolution (HR)-MS/MS. The measured methoxyacetylfentanyl concentration was 0.022-0.056mg/kg (N=3) in femoral blood, 0.12mg/kg (N=1) in urine, and 0.074mg/kg (N=1) in brain tissue homogenate. A total of 10 metabolites were identified. The observed metabolic pathways were: hydroxylation(s), N-dealkylation, O-demethylation, deamination, glucuronidation, and combinations thereof. Major analytical targets in vitro and across measured biological samples in vivo were methoxyacetylfentanyl, the O-demethyl- metabolite, and the deamide-metabolite. Intoxication with methoxyacetylfentanyl was judged as the cause of death or a major contributing factor in all three presented cases.

Pharmacokinetics and safety of fentanyl sublingual spray and fentanyl citrate intravenous: a multiple ascending dose study in opioid-naïve healthy volunteers

OBJECTIVE

Fentanyl sublingual spray, with its rapid onset for pain relief, may be efficacious in the management of acute or post-operative pain. Because patients in these settings may be opioid-naïve, the study was conducted to determine the safety, tolerability, and pharmacokinetics of multiple dose administration of fentanyl sublingual spray in an opioid-naïve population.

METHODS

Fentanyl sublingual spray (100 mcg, 200 mcg, and 400 mcg) and fentanyl citrate intravenous (IV; 50 mcg) were administered every 0.5, 1.0, 2.0, and 4.0 h for up to three doses per cohort in opioid-naïve subjects (ClinicalTrials.gov identifier: NCT02641340). Eight subjects in each cohort were randomly assigned (six subjects received fentanyl sublingual spray; two subjects received fentanyl citrate IV). Pharmacokinetic and safety-related pharmacodynamic assessments were performed through 24 h post-first dose. Safety assessments were collected through Day 7.

RESULTS

Ninety-six opioid-naïve subjects, aged 20-55 years, with a body mass index of 18.7-31.5 kg/m², participated in the study. Multiple doses of fentanyl sublingual spray (100, 200, and 400 mcg) were generally well tolerated. Hypoxia, observed in the 200-mcg and 400-mcg dose groups, increased with increasing doses and higher dosing frequency, but was readily managed by nasal cannula oxygenation. Overall, nausea increased with increasing doses, and ∼52.6% (10 out of 19) cases of nausea that occurred at the highest dose of 400 mcg were treated with concomitant medication. Overall, the reported adverse events were consistent with the known safety profile of fentanyl.

CONCLUSION

Fentanyl sublingual spray (100 mcg, 200 mg, and 400 mcg) administered every 0.5, 1, 2, and 4 h was generally well tolerated in an opioid-naïve population. The results suggest that doses of 200 mcg or lower may be safe for use in an opioid-naïve population.

Pharmacokinetics and safety of fentanyl sublingual spray and fentanyl citrate intravenous: a single ascending dose study in opioid-naïve healthy volunteers

OBJECTIVE

Fentanyl sublingual spray offers rapid pain relief in opioid-tolerant cancer patients, and may be useful in acute or post-operative pain. Both opioid-naïve and non-tolerant patients are likely to receive opioids in these settings. Understanding the relationship between systemic exposure of fentanyl sublingual spray and effects on respiratory function in opioid-naïve or non-tolerant populations is important to ensure patient safety. This study evaluated single-dose fentanyl sublingual spray in opioid-naïve participants.

RESEARCH DESIGN

Participants were randomized to receive single-dose fentanyl sublingual spray (100, 200, 400, 600, 800 mcg) or fentanyl citrate IV in one of five cohorts. Dosing occurred following a 10-h fast, with fasting continuing for 4 h post-dose. Dose proportionality was assessed using analysis of variance and linear regression techniques. PK assessments and safety monitoring were performed through 24 h post-dose. Safety assessments, including adverse event (AE) monitoring, occurred from dosing through Day 7.

RESULTS

Fifty participants (19-53 years) received fentanyl sublingual spray or fentanyl citrate IV. Mean maximum plasma concentrations were reached between 0.27-0.60 h post-dose for fentanyl sublingual spray. Peak (C_max) and total (AUC_0-t, AUC_0-∞) fentanyl exposures increased in a linear, but more than dose-proportional manner, with higher doses. The most common AEs were somnolence, nausea, and vomiting. All AEs were mild or moderate in severity. Doses at 400, 600, and 800 mcg were associated with nausea and vomiting, requiring pharmacologic intervention. Hypoxia episodes requiring nasal cannula oxygenation were observed with 600mcg and 800mcg doses.

CONCLUSIONS

Overall, single-dose fentanyl sublingual spray (100-800 mcg) was generally well tolerated, with greater incidences of AEs (e.g. nausea, vomiting, hypoxia) at higher doses. Doses up to 200 mcg may be safely administered to healthy opioid-naïve individuals with routine monitoring; doses between 400-800 mcg may be administered in settings with nasal cannula oxygenation.

Pharmacokinetics of a Transdermal Fentanyl Solution in Suffolk Sheep (Ovis aries)

Sheep used as surgical models require appropriate pain management, and the commonly used transdermal fentanyl patches require a long predosing period to achieve adequate plasma concentrations. The aim of this study was to assess the pharmacokinetic parameters of an FDA-approved transdermal fentanyl solution (TFS) that has yet to be tested in sheep. In this study, we compared TFS at 2.7 mg/kg (n = 2), 1.7 mg/kg (n = 3), and 0.5 mg/kg (n = 3) with the control fentanyl patch at 2 μg/kg/h (n = 1); both products were applied topically to the intrascapular region. Plasma concentrations showed significant interanimal variability. Severe adverse effects occurred at both 2.7 and 1.7 mg/kg TFS and mild to moderate adverse effects were noted at 0.5 mg/kg. At all 3 doses, TFS had greater maximal concentration, clearance rate, and volume of distribution; shorter time to maximal concentration; and similar half-lives to those of the patch. In addition, we validated the use of a commercial human fentanyl ELISA kit, which positively correlated with the liquid chromatography-mass spectroscopy data, but absolute values did not match. Overall, at all 3 dosages tested (0.5, 1.7, and 2.7 mg/kg), TFS delivered fentanyl plasma concentrations that exceeded the minimal effective concentration; however, adverse effects were noted at all 3 dosages. Caution and further study are required before the use of TFS in sheep can be recommended fully.

Pharmacokinetics of a Novel, Transdermal Fentanyl Solution in Rhesus Macaques (Macaca mulatta)

Rhesus macaques (Macaca mulatta) are the most commonly used NHP biomedical model and experience both research and clinical procedures requiring analgesia. Opioids are a mainstay of analgesic therapy. A novel, transdermal fentanyl solution (TFS) has been developed as a long-acting, single-administration topical opioid and was reported to provide at least 4 d of effective plasma concentrations in beagles (Canis familiaris). To evaluate the pharmacokinetic profile of TFS in healthy adult rhesus macaques, we used a 2-period, 2-treatment crossover study of a single topical administration of 1.3 (25) and 2.6 mg/kg (50 μL/kg) TFS. TFS was applied to the clipped dorsal skin of adult rhesus macaques (n = 6; 3 male, 3 female) under ketamine sedation (10 mg/kg IM). We hypothesized that TFS in rhesus macaques would provide at least 4 d of effective plasma concentrations (assumed to be ≥ 0.2 ng/mL, based on human studies). Plasma fentanyl concentrations were determined by liquid chromatography-tandem mass spectrometry before drug administration and at 0, 0.5, 1, 2, 4, 8, 12, 24, 36, 48, 60, 72, 96, 120, 144, 168, 240, 336, 408, and 504 h afterward. Noncompartmental pharmacokinetic analysis was performed. For each dose (1.3 and 2.6 mg/kg), respectively, the maximal plasma concentration was 1.95 ± 0.40 and 4.19 ± 0.69 ng/mL, occurring at 21.3 ± 4.1 and 30.7 ± 8.7 h; the AUC was 227.3 ± 31.7 and 447.0 ± 49.1 h/ng/mL, and the terminal elimination half-life was 93.7 ± 7.1 and 98.8 ± 5.4 h. No adverse effects were noted after drug administration at either dose. Macaques maintained plasma fentanyl concentrations of 0.2 ng/mL or greater for at least 7 d after 1.3 mg/kg and at least 10 d after 2.6 mg/kg topical administration of TFS. A single TFS dose may provide efficacious analgesia to rhesus macaques and reduce stress, discomfort, and risk to animals and personnel.

The uptake of transdermal fentanyl in a pregnant sheep model

OBJECTIVE

To evaluate the maternal and foetal uptake of transdermal fentanyl patch applied to the groin of pregnant sheep following surgery.

STUDY DESIGN

Prospective series.

ANIMALS

A group of 16 singleton pregnant sheep underwent anaesthesia for laparotomy, hysterotomy and instrumentation of the foetus. Of these ewes 10 (101 ± 12 days of gestation) were used to evaluate the maternal uptake of transdermal fentanyl, and the efficacy of the drug in the postoperative period (n = 10). To determine the extent of transplacental transfer of fentanyl, six ewes from the group of 10, and six other ewes (92 ± 1 days' gestation) were studied.

METHODS

A 75 μg hour^-1 fentanyl patch was placed onto the woolless skin of the medial thigh close to the groin at the end of surgery. Maternal blood samples were collected from the cephalic or jugular vein, and pain and sedation scores were determined, prior to application of the patch (time 0) and at 3, 6, 12, 24, 36 and 48 hours after. A commercial Fentanyl ELISA kit was used to determine the concentration of fentanyl. Paired maternal and foetal blood samples were collected 48 hours after surgery. Animals were euthanized at the end of the study. Data were tested for normality and compared with Student t test or one-way anova and are expressed as mean ± standard deviation or median (range).

RESULTS

Recovery from anaesthesia and surgery was uneventful in all ewes. The dose of fentanyl was 1.4 ± 0.2 μg kg^-1 hour^-1. The maximum maternal plasma concentration of fentanyl was 0.547 ng mL^-1 (range, 0.349-0.738 ng mL^-1) at 12 hours. After 48 hours, the concentration of fentanyl was 0.381 ng mL^-1 (range, 0.211-0.487 ng mL^-1; maternal) and 0.295 ng mL^-1 (range, 0.185-0.377 ng mL^-1; foetal; p = 0.175). The placental transfer rate of fentanyl was 77%.

CONCLUSIONS AND CLINICAL RELEVANCE

The uptake of fentanyl varied between animals. The placental transfer rate of fentanyl was 77%.

Successful protocol of anaesthesia for measuring transepithelial nasal potential difference in spontaneously breathing mice

Numerous difficulties arise during in vivo measurements of transepithelial nasal potential difference (PD) in mice, such as inadequate duration and depth of anaesthesia, bronchoaspiration of solutions perfused in the nose, and respiratory and/or cardiovascular depression.

Anaesthesia was induced in adult C57 mice with intraperitoneal injection of a combination of fentanyl, droperidol and medetomidine, each of these at either a small dose (0.20, 10 and 0.33 mg/kg, respectively) or at a large dose (0.40, 20 and 0.40 mg/kg, respectively), combined with a fixed dose of 0.375 μg clonidine. In order to establish a pharmacokinetic–pharmacodynamic relationship, blood concentrations of the first three drugs were measured in 24 animals by liquid-chromatography tandem mass spectrometry. At the end of the experiment, naloxone, a competitive morphinic antagonist, and atipamezole, an α-2 adrenergic antagonist, were administered. Bronchoaspiration was prevented by tilting the animal head downwards and by absorbing the excess fluid from the opposite nostril and from the oral cavity. Optimal assessment of anaesthesia associated with regular respiration, loss of blink, pupillary and pedal withdrawal reflexes was obtained with doses of fentanyl, droperidol and medetomidine corresponding to 0.20, 20 and 0.40 mg/kg, respectively. Blood concentrations of fentanyl around 17 ng/mL induced loss of respiratory efforts and were followed by death during the experiment. Integrity of ion transport was demonstrated under continuous perfusion by successive depolarization after amiloride and repolarization after chloride-free solution.

The combination investigated in this study lead to adequate surgical anaesthesia (stage III, plane 2) for prolonged nasal PD measurements in spontaneously breathing mice.

The Influence of Low Salivary Flow Rates on the Absorption of a Sublingual Fentanyl Citrate Formulation for Breakthrough Cancer Pain

CONTEXT

Salivary gland hypofunction may affect the absorption of drugs through the oral mucosa, which in turn may affect their clinical efficacy (e.g., onset of action).

OBJECTIVES

The aim of this study was to assess the pharmacokinetics of a sublingual fentanyl orally disintegrating tablet (Abstral, Prostrakan Inc.) in a group of cancer patients with salivary gland hypofunction.

METHODS

Nine cancer patients with salivary gland hypofunction underwent a series of three pharmacokinetic studies with the sublingual fentanyl orally disintegrating tablet. In the first phase, the patients received no pretreatment; in the second phase, the patients were allowed to moisten the oral cavity before dosing; in the third phase, the patients were given pilocarpine hydrochloride (saliva stimulant) before dosing. Fentanyl concentrations were measured using a method of high-performance liquid chromatography with validated tandem mass spectrometric detection.

RESULTS

The Tmax was longer, the Cmax was lower, the AUC0-30 lower, and the AUClast lower in the phase involving no pretreatment; the Tmax/Cmax/AUC0-30/AUClast were similar in the phase involving moistening of the oral cavity and the phase involving giving pilocarpine hydrochloride.

CONCLUSION

The pharmacokinetics of the sublingual fentanyl orally disintegrating tablet appear to be negatively affected by the presence of salivary gland hypofunction, although the moistening of the oral cavity before dosing results in a pharmacokinetic profile similar to that seen with the giving of pilocarpine hydrochloride.

Comparison of the Efficacy and Safety of a Pharmacokinetic Model-Based Dosing Scheme Versus a Conventional Fentanyl Dosing Regimen For Patient-Controlled Analgesia Immediately Following Robot-Assisted Laparoscopic Prostatectomy: A Randomized Clinical Trial

Conventional, intravenous, patient-controlled analgesia, which is only administered by demand bolus without basal continuous infusion, is closely associated with inappropriate analgesia. Pharmacokinetic model-based dosing schemes can quantitatively describe the time course of drug effects and achieve optimal drug therapy. We compared the efficacy and safety of a conventional dosing regimen for intravenous patient-controlled analgesia that was administered by demand bolus without basal continuous infusion (group A) versus a pharmacokinetic model-based dosing scheme performed by decreasing the dosage of basal continuous infusion according to the model-based simulation used to achieve a targeted concentration (group B) following robot-assisted laparoscopic prostatectomy.In total, 70 patients were analyzed: 34 patients in group A and 36 patients in group B. The postoperative opioid requirements, pain scores assessed by the visual analog scale, and adverse events (eg, nausea, vomiting, pruritis, respiratory depression, desaturation, sedation, confusion, and urinary retention) were compared on admission to the postanesthesia care unit and at 0.5, 1, 4, 24, and 48 h after surgery between the 2 groups. All patients were kept for close observation in the postanesthesia care unit for 1 h, and then transferred to the general ward.The fentanyl requirements in the postanesthesia care unit for groups A and B were 110.0 ± 46.4 μg and 77.5 ± 35.3 μg, respectively. The pain scores assessed by visual analog scale at 0.5, 1, 4, and 24 h after surgery in group B were significantly lower than in group A (all P < 0.05). There were no differences in the adverse events between the 2 groups.We found that the pharmacokinetic model-based dosing scheme resulted in lower opioid requirements, lower pain scores, and no significant adverse events in the postanesthesia care unit following robot-assisted laparoscopic prostatectomy in comparison with conventional dosing regimen.

Pharmacokinetics of 2 Formulations of Transdermal Fentanyl in Cynomolgus Macaques (Macaca fascicularis)

Fentanyl is a μ-opioid agonist that often is used as the analgesic component for balanced anesthesia in both human and veterinary patients. Minimal information has been published regarding appropriate dosing, and the pharmacokinetics of fentanyl are unknown in NHP. The pharmacokinetic properties of 2 transdermal fentanyl delivery methods, a solution (2.6 and 1.95 mg/kg) and a patch (25 μg/h), were determined when applied topically to the dorsal scapular area of cynomolgus macaques (Macaca fascicularis). Serum fentanyl concentrations were analyzed by using liquid chromatography-mass spectrometry. Compared with the patch, the transdermal fentanyl solution generated higher drug concentrations over longer time. Adverse reactions occurred in the macaques that received the transdermal fentanyl solution at 2.6 mg/kg. Both preparations showed significant interanimal variability in the maximal serum drug levels, time to achieve maximal fentanyl levels, elimination half-life, and AUC values. Both the maximal concentration and the time at which this concentration occurred were increased in macaques compared with most other species after application of the transdermal fentanyl patch and compared with dogs after application of the transdermal fentanyl solution. The pharmacokinetic properties of transdermal fentanyl in macaques are markedly different from those in other veterinary species and preclude its use as a long-acting analgesic drug in NHP.

Opioid Concentrations in Oral Fluid and Plasma in Cancer Patients With Pain

CONTEXT

Measuring opioid concentrations in pain treatment is warranted in situations where optimal opioid analgesia is difficult to reach.

OBJECTIVES

To assess the usefulness of oral fluid (OFL) as an alternative to plasma in opioid concentration monitoring in cancer patients on chronic opioid therapy.

METHODS

We collected OFL and plasma samples from 64 cancer patients on controlled-release (CR) oral morphine, CR oral oxycodone, or transdermal (TD) fentanyl for pain. Samples were obtained on up to five separate days.

RESULTS

A total of 213 OFL and plasma samples were evaluable. All patients had detectable amounts of the CR or TD opioid in both plasma and OFL samples. The plasma concentrations of oxycodone and fentanyl (determination coefficient R(2) = 0.628 and 0.700, respectively), but not morphine (R(2) = 0.292), were moderately well correlated to the daily opioid doses. In contrast to morphine and fentanyl (mean OFL/plasma ratio 2.0 and 3.0, respectively), the OFL oxycodone concentrations were significantly higher than the respective plasma concentrations (mean OFL/plasma ratio 14.9). An active transporter could explain the much higher OFL vs. plasma concentrations of oxycodone compared with morphine and fentanyl.

CONCLUSION

OFL analysis is well suited for detecting the studied opioids. For morphine and fentanyl, an approximation of the plasma opioid concentrations is obtainable, whereas for oxycodone, the OFL/plasma concentration relationship is too variable for reliable approximation results.

Saliva versus Plasma for Pharmacokinetic and Pharmacodynamic Studies of Fentanyl in Patients with Cancer

PURPOSE

Fentanyl is widely used to relieve cancer pain. However there is great interpatient variation in the dose required to relieve pain and little knowledge about the pharmacokinetic and pharmacodynamic (PK/PD) relationship of fentanyl and pain control. Patients with cancer are fragile and there is reluctance on the part of health professionals to take multiple plasma samples for PK/PD studies. The relationship between plasma and saliva fentanyl concentrations was investigated to determine whether saliva could be a valid substitute for plasma in PK/PD studies.

METHODS

One hundred sixty-three paired plasma and saliva samples were collected from 56 patients prescribed transdermal fentanyl (Durogesic, Janssen-Cilag Pty Limited, NSW, Australia) at varying doses (12-200 µg/h). Pain scores were recorded at the time of sampling. Fentanyl and norfentanyl concentrations in plasma and saliva were quantified using HPLC-MS/MS.

FINDINGS

Saliva concentrations of fentanyl (mean = 4.84 μg/L) were much higher than paired plasma concentrations of fentanyl (mean = 0.877 μg/L). Both plasma and saliva mean concentrations of fentanyl were well correlated with dose with considerable interpatient variation at each dose. The relationship between fentanyl and norfentanyl concentrations was poor in both plasma and saliva. No correlation was observed between fentanyl concentration in plasma and saliva (r(2) = 0.3743) or free fentanyl in plasma and total saliva concentrations (r(2) = 0.1374). Pain scores and fentanyl concentration in either of the matrices were also not correlated.

IMPLICATIONS

No predictive correlation was observed between plasma and saliva fentanyl concentration. However the detection of higher fentanyl concentrations in saliva than plasma, with a good correlation to dose, may allow saliva to be used as an alternative to plasma in PK/PD studies of fentanyl in patients with cancer.

Transmucosal Immediate-Release Fentanyl for Breakthrough Cancer Pain: Opportunities and Challenges for Use in Palliative Care

Opioids are used to treat breakthrough cancer pain (BTCP) and can be classified by relative duration and onset of action. Regulatory approvals of numerous transmucosal immediate-release fentanyl (TIRF) formulations provide alternative options to palliative care-trained providers in the management of BTCP. TIRFs have been formulated as a sublingual tablet, sublingual spray, intranasal spray, pectin-based nasal spray, buccal tablet, and buccal soluble film. Differences exist between TIRFs regarding formulation design and dosing to treat BTCP. Opportunities for use include palliation of BTCP in head and neck cancer and/or radiation-induced mucositis. The purpose of this review is to discuss TIRF formulation and dosing, pharmacokinetics, clinical efficacy, patient acceptability, and safety/tolerability. In addition, barriers to TIRF utilization will be discussed.

[Metabolism of designer drugs. The fentanyl derivatives]

This literature review is focused on the studies of metabolism of designer drugs, with special reference to fentanyl derivatives. Certain physicochemical characteristics of the main metabolites most frequently encountered in the illegal trade of the fentanyl group analgesics have been calculated. The proposed recommendations include the methods for the identification of certain fentanyl derivatives during analysis of biological media.

Endogenous Opioid Mechanisms Are Implicated in Obesity and Weight Loss in Humans

CONTEXT

Successful long-term weight loss is challenging. Brain endogenous opioid systems regulate associated processes; however, their role in the maintenance of weight loss has not been adequately explored in humans.

OBJECTIVE

In a preliminary study, the objective was to assess central μ-opioid receptor (MOR) system involvement in eating behaviors and their relationship to long-term maintenance of weight loss.

DESIGN

This was a case-control study with follow-up of the treatment group at 1 year after intervention.

SETTING

The study was conducted at a tertiary care university medical center.

PARTICIPANTS

Lean healthy (n = 7) and chronically obese (n = 7) men matched for age and ethnicity participated in the study.

INTERVENTIONS

MOR availability measures were acquired with positron emission tomography and [(11)C]carfentanil. Lean healthy men were scanned twice under both fasted and fed conditions. Obese men were placed on a very low-calorie diet to achieve 15% weight loss from baseline weight and underwent two positron emission tomography scans before and two after weight loss, incorporating both fasted and fed states.

MAIN OUTCOME MEASURES

Brain MOR availability and activation were measured by reductions in MOR availability (nondisplaceable binding potential) from the fed compared with the fasted-state scans.

RESULTS

Baseline MOR nondisplaceable binding potential was reduced in obese compared with the lean and partially recovered obese after weight loss in regions that regulate homeostatic, hedonic, and emotional responses to feeding. Reductions in negative affect and feeding-induced MOR system activation in the right temporal pole were highly correlated in leans but not in obese men. A trend for an association between MOR activation in the right temporal pole before weight loss and weight regain 1 year was found.

CONCLUSIONS

Although these preliminary studies have a small sample size, these results suggest that obesity and diet-induced weight loss impact central MOR binding and endogenous opioid system function. MOR system activation in response to an acute meal may be related to the risk of weight regain.

Adding fentanyl to etomidate fails to reduce painful recall of external direct current cardioversion in adults: a randomised trial

INTRODUCTION

External electrical cardioversion under hypnotics, even when combined with opioids, has been consistently described as distressing or painful. The main objective of the present study was to determine if adding an opioid to a hypnotic, in comparison to the same hypnotic alone, would decrease the incidence of unpleasant or painful recall during anaesthesia for external electrical cardioversion.

METHODS

This was a single-centre, prospective, randomised, double-blinded clinical trial that took place from September 2011 to March 2012. Fifty-two adult patients with persistent atrial fibrillation, scheduled for external direct current cardioversion, were enrolled. Exclusion criteria were age >80 years, previous cardiac surgery, implanted pacemaker or defibrillator, and haemodynamic instability. Patients received intravenously either (group EF) fentanyl 50 g and after 60 s etomidate 0.1 mg/kg, or (group E) only etomidate 0.1 mg/kg. If the patients did not lose their eyelid reflex, repeated doses of etomidate 4 mg were given. Cardioversion was attempted with an extracardiac biphasic electrical shock from 200 to 300 J, at most three times. The primary endpoint was recall of something unpleasant or painful. Secondary outcome measures were predictors of the requirement for repeat doses of etomidate, and the number of shocks needed.

RESULTS

Fifty-one patients (35 male, 16 female), aged 62.1 ± 10.2 years, completed the study. There were no differences between group EF and group E regarding recall (unpleasant recall 0 vs. 2 patients, p=0.235; painful recall 1 vs. 0 patients, p=0.510). The administration of etomidate alone was a significant predictor for subsequent repeated doses of etomidate (p=0.049, odds ratio 4.312, 95% confidence interval 1.007-18.460). The number of shocks needed to restore sinus rhythm did not differ between the groups (p=0.846).

CONCLUSIONS

In the present study, the addition of fentanyl to etomidate did not diminish distressing or painful experience during anaesthesia for external cardioversion.

The interaction of nitrous oxide and fentanyl on the minimum alveolar concentration of sevoflurane blocking motor movement (MACNM) in dogs

The study objective was to determine the effects of 70% nitrous oxide (N2O) and fentanyl on the end-tidal concentration of sevoflurane necessary to prevent movement (MACNM) in response to noxious stimulation in dogs. Six healthy, adult, intact male, mixed-breed dogs were used on 3 occasions in a randomized crossover design. After induction of anesthesia with sevoflurane, each of the following treatments was randomly administered: fentanyl loading dose (Ld) of 15 μg/kg and infusion of 6 μg/kg per hour [treatment 1 (T1)], 70% N2O (T2), or fentanyl (Ld of 15 μg/kg and infusion of 6 μg/kg per hour) combined with 70% N2O (T3). Each dog received each of the 3 treatments once during the 3-week period. Determination of MACNM was initiated 90 min after the start of each treatment. The values were compared using the baseline MACNM, which had been determined in a previous study on the same group of dogs. Data were analyzed using a mixed-model analysis of variance (ANOVA) and Tukey-Kramer tests, and expressed as least squares mean ± SEM. The baseline MACNM decreased by 36.6 ± 4.0%, 15.0 ± 4.0%, and 46.0 ± 4.0% for T1, T2, and T3, respectively (P < 0.05), and differed (P < 0.05) among treatments. Mean fentanyl plasma concentrations did not differ (P ≥ 0.05) between T1 (3.70 ± 0.56 ng/mL) and T3 (3.50 ± 0.56 ng/mL). The combination of fentanyl and N2O resulted in a greater sevoflurane MACNM sparing effect than either treatment alone.

[Chronic non-cancer-related pain. Long-term treatment with rapid-release and short-acting opioids in the context of misuse and dependency]

Annually published data show a continual increase in the volume of opioid prescriptions in Germany, thus indicating an intensification of opioid therapy. The majority of opioids are prescribed to treat chronic non-cancer-related pain. On the basis of current guidelines, as well as in terms of the lack of data regarding long-term use of opioids and their effectiveness beyond a period of 3 months, this development must be viewed critically. With reference to four case reports, we discuss and evaluate opioid therapy in relation to medication misuse and the development of drug dependency. Particular emphasis is placed on the administration of rapid-release and short-acting opioid preparations, which we consider to be particularly problematic.

Lessons learned from hospice care

Pharmaceutical care of the hospice patient offers unique challenges in the management of pain and other symptoms. Lessons learned in providing hospice care can be used in the care of nonterminal patients as well to optimize patient-specific care, regardless of care setting or life expectancy.

Mapping neurotransmitter networks with PET: an example on serotonin and opioid systems

All functions of the human brain are consequences of altered activity of specific neural pathways and neurotransmitter systems. Although the knowledge of "system level" connectivity in the brain is increasing rapidly, we lack "molecular level" information on brain networks and connectivity patterns. We introduce novel voxel-based positron emission tomography (PET) methods for studying internal neurotransmitter network structure and intercorrelations of different neurotransmitter systems in the human brain. We chose serotonin transporter and μ-opioid receptor for this analysis because of their functional interaction at the cellular level and similar regional distribution in the brain. Twenty-one healthy subjects underwent two consecutive PET scans using [(11)C]MADAM, a serotonin transporter tracer, and [(11)C]carfentanil, a μ-opioid receptor tracer. First, voxel-by-voxel "intracorrelations" (hub and seed analyses) were used to study the internal structure of opioid and serotonin systems. Second, voxel-level opioid-serotonin intercorrelations (between neurotransmitters) were computed. Regional μ-opioid receptor binding potentials were uniformly correlated throughout the brain. However, our analyses revealed nonuniformity in the serotonin transporter intracorrelations and identified a highly connected local network (midbrain-striatum-thalamus-amygdala). Regionally specific intercorrelations between the opioid and serotonin tracers were found in anteromedial thalamus, amygdala, anterior cingulate cortex, dorsolateral prefrontal cortex, and left parietal cortex, i.e., in areas relevant for several neuropsychiatric disorders, especially affective disorders. This methodology enables in vivo mapping of connectivity patterns within and between neurotransmitter systems. Quantification of functional neurotransmitter balances may be a useful approach in etiological studies of neuropsychiatric disorders and also in drug development as a biomarker-based rationale for targeted modulation of neurotransmitter networks.

Pharmacokinetics, Tolerability, and Performance of a Novel Matrix Transdermal Delivery System of Fentanyl Relative to the Commercially Available Reservoir Formulation in Healthy Subjects

A novel transdermal formulation of fentanyl-containing dipropylene glycol droplets dispersed in a silicone matrix with a rate-controlling membrane was developed. Healthy male subjects (n = 24) received repeated 72-hour applications of fentanyl (50 mug/h) as the novel matrix and the conventional reservoir formulations in a randomized, 2-way crossover study. Blood samples were collected, and serum concentrations of fentanyl were assayed using liquid chromatography with mass spectrometry detection. The mean area under the curve (AUCtau) and peak concentrations (C(max)) of the matrix formulation were 84 838 pg.h/mL and 1680 pg/mL, respectively. Ratio and 90% confidence intervals of AUCtau and C(max) between the 2 formulations were within 80% to 125%. Adherence of the matrix formulation was higher than the reservoir formulation (62.5 vs 56.2%, P < .0001), without affecting skin irritation. Vital signs and adverse events of the 2 formulations were similar in nature and frequency. The novel matrix formulation displayed enhanced adherence and resulted in similar pharmacokinetics and tolerability as the reservoir formulation.

Quantitative study of controlled substance bedside wasting, disposal and evaluation of potential ecologic effects

Drugs in wastewater arise from many sources. For health care, these include excretion and direct disposal (bedside wasting). The present study reports on the dispensing and wasting of 15 controlled substances (CS) at two health care facilities in Albany, NY over a nearly two year period. The study considered measures of ecotoxicity, drug metabolism, excretion and disposal of these CS. Potential alternatives to flushing of CS into wastewaters from healthcare facilities are discussed. Drug medication and waste collection records (12,345) included: numbers of drugs dispensed, returned and wasted. Overall, 8528 g of 15 CS were wasted. Three (midazolam, acetaminophen-codeine and fentanyl) accounted for 87.5% of the total wasted. Wasting varied by hospital, 14 CS at the academic medical center hospital and 8 at the surgical care center were wasted. Liquids were more frequently wasted than tablets or pills. Some combination drugs (acetaminophen (APAP)-codeine) were frequently (50% of drug dispensed) wasted while others were less wasted (APAP-hydrocodone-6.3%; APAP-oxycodone-1.3%). The 8 CS judged more hazardous to aquatic life were: APAP-codeine, APAP-hydrocodone, APAP-oxycodone, alprazolam, diazepam, fentanyl, midazolam, and testosterone. Ketamine, morphine, oxycodone and zolpidem were of lesser acute toxicity based on available LC50 values. These CS might provide a therapeutically equivalent alternative to the more environmentally harmful drugs. In health care facilities, professionals dispose of CS by bedside wasting into water or other receptacles. This can be avoided by returning CS to the hospital's pharmacy department, thence to a licensed distributor. Study of this process of drug wasting can identify opportunities for process improvements. We found 3 CS (APAP-codeine, midazolam and testosterone) where ½ to 1/3 of the drug was wasted and 5 others with 30 to 13% wasted. Knowledge of the adverse impacts from the release of highly toxic drugs into the environment might influence CS selection and disposal alternatives.

Effects of Application Site and Subject Demographics on the Pharmacokinetics of Fentanyl HCl Patient-Controlled Transdermal System (PCTS)

INTRODUCTION

The fentanyl HCl patient-controlled transdermal system (PCTS) is a self-contained, preprogrammed, needle-free system currently in development for acute pain management in a medically supervised setting. The objectives of these studies were to evaluate skin application sites for the fentanyl HCl PCTS and to evaluate the effect of patient demographics on its pharmacokinetics.

METHODS

The first study was a randomised, open-label, single-centre, 3-treatment, crossover study in which the fentanyl HCl PCTS was applied to the upper outer arm, lower inner arm or chest of healthy volunteers. Fentanyl 25 microg was then delivered via this system twice during the first 20 minutes of every hour for 24 hours. The pharmacokinetics of fentanyl were determined and analysed for each application site using ANOVA. The second study was a nonrandomised, nonblind, multicentre, sequential treatment study. Healthy volunteers received fentanyl HCl 40 microg via the PCTS three times during the first 30 minutes of each hour for 3 hours. After a 5- to 10-day washout period, fentanyl HCl 120 microg was administered intravenously during the first 30 minutes of each hour for 3 hours as a reference treatment. Pharmacokinetic parameters were determined for the fentanyl HCl PCTS, and results were analysed using ANOVA. Safety and tolerability were evaluated in both studies.

RESULTS

Application of the system to the upper outer arm or chest resulted in similar maximum serum concentrations (Cmax; 1.193 and 1.176 microg/L, respectively) and areas under the serum concentration-time curve (AUC24-25; 1.033 and 1.015 microg h/L). However, both Cmax and AUC24-25 were less when the system was applied to the lower inner arm (0.859 microg/L and 0.757 microg x h/L). Subject age, bodyweight, sex and ethnicity had no significant effect on pharmacokinetic parameters. No serious adverse events were reported in either study during or after administration of the fentanyl HCl PCTS.

CONCLUSION

Fentanyl HCl is comparably absorbed from the PCTS when it is applied to the upper outer arm or chest. The pharmacokinetics of fentanyl HCl delivered by the PCTS are unaffected by sex, age, race or weight.

Characterisation of the Pharmacokinetics of the Fentanyl HCl Patient-Controlled Transdermal System (PCTS)

INTRODUCTION

The fentanyl HCl patient-controlled transdermal system (PCTS) is a self-contained, preprogrammed, noninvasive analgesic delivery system for acute pain management. We carried out three studies with the following objectives: study I to evaluate the relationship between fentanyl absorption and the magnitude of current applied to the system; study II to determine dose-proportionality for the fentanyl HCl PCTS (25 and 40 microg); and study III to describe the effects of single- and multiple-day administration on the pharmacokinetics of fentanyl delivered by the PCTS.

METHODS

All studies were open-label, crossover studies with washout periods between treatments. In study I, randomised participants (n = 36) received three of a potential five fentanyl HCl PCTS prototypes, each of which used a different current magnitude, and each of which was evaluated for 24 hours. In study II, participants (n = 40) received fentanyl (25 microg) from the PCTS for 23.33 hours, followed by fentanyl (40 microg) from the PCTS for 23.33 hours. Intravenous (IV) fentanyl (80 microg/h) was administered intermittently over 24 hours as a reference treatment in Studies I and II. In study III, participants (n = 28) received fentanyl (40 microg) from the PCTS for 20 hours, followed by fentanyl (40 microg) from the PCTS for 68 hours. Pharmacokinetic parameters, including maximum serum fentanyl concentration (Cmax), time to Cmax (tmax), area under the serum concentration-time curve (AUC) and terminal half-life (t(1/2)), were determined for each treatment.

RESULTS

The amount of fentanyl absorbed from the PCTS was linearly dependent on the magnitude of current applied to the system, with a current of 170 microA resulting in the absorption of 39.5 microg of fentanyl at hour 23. Mixed-effect ANOVA indicated no significant difference (p > 0.1) in the dose-normalised pharmacokinetics of the fentanyl HCl PCTS 25 and 40 microg. No significant difference existed between the corrected AUC(0-5) of the fentanyl HCl PCTS during the single- and multiple-day treatment periods (0.40 and 0.54 microg x h/L, respectively; p = 0.133). The system was well tolerated, with headache and mild application site erythema being the most common treatment-related adverse events.

CONCLUSIONS

A linear relationship exists between the amount of current applied to the fentanyl HCl PCTS and the amount of fentanyl absorbed. There is dose-proportionality in the pharmacokinetics of the fentanyl HCl PCTS 25 and 40 microg. Multiple-day administration does not affect the pharmacokinetics of the fentanyl HCl PCTS 40 microg. The system was well tolerated, even after repeated application.

The Effect of Dosing Frequency on the Pharmacokinetics of a Fentanyl HCl Patient-Controlled Transdermal System (PCTS)

INTRODUCTION

The fentanyl HCl patient-controlled transdermal system (PCTS) is a noninvasive, needle-free, credit card-sized drug delivery system designed for the on-demand management of acute pain in a medically supervised setting. The objective of these studies was to determine the effect of dosing frequency on the pharmacokinetics of fentanyl delivered by the PCTS.

METHODS

All three studies were single-centre, open-label, randomised, crossover studies. The fentanyl HCl PCTS was applied to the upper outer arm of all participants. In the first study, participants (n = 30) received three fentanyl HCl PCTS 25 microg treatments: two sequential doses hourly for 23.33 hours, six sequential doses every 3 hours for 22 hours, and 72 doses continuously over 12 hours. Participants (n = 31) in the second study received three fentanyl HCl PCTS 40 microg treatments: two sequential doses hourly over 23.33 hours, six sequential doses every 3 hours over approximately 10 hours, and 80 doses continuously over 13.33 hours. In the third study, participants (n = 28) received four fentanyl HCl PCTS 40 microg treatments: 6, 18, 36 and 80 doses over 1, 3, 6 and 13.33 hours, respectively. Naltrexone was used to block the opioid effects of fentanyl. Pharmacokinetic parameters, including maximum serum fentanyl concentration (Cmax), time to Cmax (tmax), area under the serum concentration-time curve (AUC) and terminal half-life (t(1/2)) were determined.

RESULTS

In the first study, the dose-normalised AUC (AUCn) values for the 2- and 6-dose sequence treatments were not significantly different (p = 0.937), suggesting that the frequency of dosing has little effect on the amount of fentanyl absorbed; however, the AUCn for the 72-dose treatment was significantly lower than that of the other treatments (p = 0.001), which were of longer duration. The results of the second study paralleled those from the first, suggesting that the bioavailability of fentanyl delivered by the PCTS increases as a function of time and is likely to be independent of dosing frequency. Results from the third study suggested that approximately 40% of the nominal 40 microg fentanyl dose is absorbed during the first hour of treatment, with the full nominal dose absorbed after approximately 10 hours. The fentanyl HCl PCTS was well tolerated.

CONCLUSION

The amount of fentanyl absorbed from the PCTS increases as a function of time and is independent of both dosing frequency and total number of doses delivered. The fentanyl HCl PCTS is generally safe and well tolerated.

A review of the pharmacokinetic profile of transmucosal fentanyl formulations

BACKGROUND AND OBJECTIVES

Breakthrough pain (BTP) is a transitory flare of moderate-to-severe pain that occurs in patients with stable, controlled persistent pain. Management of BTP episodes is difficult because frequency, time-to-peak intensity, and duration of episodes vary both within and between individuals. Formulations of fentanyl that use a buccal, sublingual, or nasal transmucosal route of administration have been developed for the treatment of BTP in opioid-tolerant patients with cancer. These formulations allow rapid passage into the bloodstream and avoid first-pass metabolism and, therefore, are more likely to match the time-course of BTP episodes than are oral formulations. The purposes of this analysis were to identify and review published data describing the pharmacokinetic properties of rapid-onset fentanyl formulations and to evaluate these properties in view of the temporal dynamic characteristics of BTP in order to help guide medical practice.

METHODS

Relevant publications were searched in the PubMed database from 1998. The plasma drug concentration-time profile of each formulation obtained from the identified studies was adjusted to a consistent scale for comparison.

RESULTS

The data revealed that the various transmucosal formulations resulted in three typical plasma fentanyl concentration profiles: (1) type 1: a very rapid rise and short duration; (2) type 2: a rapid increase and sustained intensity; and (3) type 3: a slower onset and longer duration.

CONCLUSIONS

Given the substantial variability of BTP episodes experienced by patients, these pharmacokinetic differences may provide useful information for a physician who is selecting a rapid-onset opioid medication for a patient.

Increase in specific density of levobupivacaine and fentanyl solution ensures lower incidence of inadequate block

The clinical presentation of a subarachnoid block (SAB) is dependent upon the intrathecal spread of local anesthetic (LA). Intrathecal distribution depends on the chemical and physical characteristics of LA, puncture site, technique used, patient anatomical characteristics and hydrodynamic properties of cerebrospinal fluid. We tried to determine whether a combined glucose/LA solution can render a clinically significant difference in sensory block distribution and motor block intensity.This was a controlled, randomized and double blinded study. The surgical procedures were stripping of the great or small saphenous vein and extirpation of remaining varicose veins. The study included 110 patients distributed into two groups: Hyperbaric (7.5 mg levobupivacaine (1.5 ml 0.5% Chirocaine) + 50 microg Fentanyl (0.5 ml Fentanil) and 1 ml 10% glucose (Pliva)) vs. Hypobaric (7.5 mg levobupivacaine (1.5 ml 0.5% Chirocaine) + 50 microg Fentanyl (0.5 ml Fentanil) and 1 ml 0.9% NaCl (Pliva, Zagreb)) adding to a total volume of 3.5 ml per solution. Spinal puncture was at L3-L4 level. Spinal block distribution was assessed in five minute intervals and intensity of motor block was assessed according to the modified Bromage scale. Pain was assessed with the Visual Analogue Scale. A statistically significant difference in sensory block distribution, motor block intensity and recovery time was established between hyperbaric and hypobaric solutions. By increasing the specific density of anesthetic solution, a higher sensory block, with lesser variability, a diminished influence of Body Mass Index, decreased motor block intensity and faster recovery time may be achieved.

Mild hypothermia decreases fentanyl and midazolam steady-state clearance in a rat model of cardiac arrest

OBJECTIVES

Therapeutic hypothermia is widely employed for neuroprotection after cardiac arrest. However, concern regarding elevated drug concentrations during hypothermia and increased adverse drug reaction risk complicates concurrent pharmacotherapy. Many commonly used medications in critically ill patients rely on the cytochrome P450 3A isoform for their elimination. Therefore, our study objectives were to determine the effect of mild hypothermia on the in vivo pharmacokinetics of fentanyl and midazolam, two clinically relevant cytochrome P450 3A substrates, after cardiac arrest and to investigate the mechanisms of these alterations.

DESIGN

Prospective, randomized, controlled study.

SETTING

University research laboratory.

SUBJECTS

Thirty-two adult male Sprague-Dawley rats.

INTERVENTIONS

An asphyxial cardiac arrest rat model was used and mild hypothermia (33°C) was induced 1 hr post injury by surface cooling and continued for 10 hrs to mimic the prolonged clinical application of hypothermia accompanied by intensive care interventions. Fentanyl and midazolam were independently administered by intravenous infusion and plasma and brain concentrations were analyzed using ultraperformance liquid chromatography tandem mass spectrometry. Cytochrome P450 3a2 protein expression was measured and a Michaelis-Menten enzyme kinetic analysis was performed at 37°C and 33°C using control rat microsomes.

MEASUREMENTS AND MAIN RESULTS

Mild hypothermia decreased the systemic clearance of both fentanyl (61.5 ± 11.5 to 48.9 ± 8.95 mL/min/kg; p < .05) and midazolam (89.2 ± 12.5 to 73.6 ± 12.1 mL/min/kg; p < .05) after cardiac arrest. The elevated systemic concentrations did not lead to parallel increased brain exposures of either drug. Mechanistically, no differences in cytochrome P450 3a2 expression was observed, but the in vitro metabolism of both drugs was decreased at 33°C vs. 37°C through reductions in enzyme metabolic capacity rather than substrate affinity.

CONCLUSIONS

Mild hypothermia reduces the systemic clearances of fentanyl and midazolam in rats after cardiac arrest through alterations in cytochrome P450 3a2 metabolic capacity rather than enzyme affinity as observed with other cytochrome P450s. Contrasting effects on blood and brain levels further complicates drug dosing. Consideration of the impact of hypothermia on medications whose clearance is dependent on P450 3A metabolism is warranted.

[Application of three compartment model and response surface model to clinical anesthesia using Microsoft Excel]

With the spread of total intravenous anesthesia, clinical pharmacology has become more important. We report Microsoft Excel file applying three compartment model and response surface model to clinical anesthesia. On the Microsoft Excel sheet, propofol, remifentanil and fentanyl effect-site concentrations are predicted (three compartment model), and probabilities of no response to prodding, shaking, surrogates of painful stimuli and laryngoscopy are calculated using predicted effect-site drug concentration. Time-dependent changes in these calculated values are shown graphically. Recent development in anesthetic drug interaction studies are remarkable, and its application to clinical anesthesia with this Excel file is simple and helpful for clinical anesthesia.

Long-term effectiveness and tolerability of sublingual fentanyl orally disintegrating tablet for the treatment of breakthrough cancer pain

BACKGROUND AND OBJECTIVES

Breakthrough cancer pain (BTcP) is a transient exacerbation of cancer pain in patients with otherwise stable, persistent background pain. This study evaluated the long-term effectiveness and tolerability of sublingual fentanyl orally disintegrating tablet (sublingual fentanyl ODT), for the treatment of BTcP in opioid-tolerant patients with cancer.

RESEARCH DESIGN AND METHODS

This was a non-randomized, open-label, multi-center, Phase III study conducted in opioid-tolerant patients (aged ≥17 years) with BTcP. The study comprised a 2-week titration phase, followed by a maintenance phase of up to 12 months. Patients self-administered sublingual fentanyl ODT for episodes of BTcP. Effectiveness was assessed using patients' global evaluation of medication (PGEM), the brief pain inventory (BPI) and the depression, anxiety and positive outlook scale (DAPOS). Adverse events were recorded throughout.

CLINICAL TRIAL REGISTRATION

NCT00263575 (http://www.clinicaltrials.gov/).

RESULTS

Of 139 recruited patients, 69% identified an effective dose of sublingual fentanyl ODT (a dosage that successfully treated all episodes of BTcP over two consecutive days) and entered the maintenance phase, during which they were treated for a median of 149.0 days (mean dose 507.5 µg). The study recorded a significant increase in reported satisfaction with pain medication at the 6-month and end-of-study visits, compared to screening (p ≤ 0.01). Evaluation of quality of life using BPI and DAPOS identified no deterioration in scores and significant improvements in certain parameters (p < 0.05). Sublingual fentanyl ODT was well tolerated, with no study drug-related deaths, and 49 patients (35.3%) experiencing ≥1 study drug-related adverse event. The most common of these included nausea (8.6%), constipation (5.8%) and somnolence (5.8%). There was no evidence of sublingual mucosal irritation due to the study medication. The pattern of adverse events was similar to that previously observed with transmucosal fentanyl.

CONCLUSIONS

Sublingual fentanyl ODT was effective and well tolerated for the long-term treatment of BTcP in opioid-tolerant cancer patients. There was an increase in satisfaction with pain medication during the study, and sublingual fentanyl ODT showed an acceptable safety profile over 12 months of treatment.

Bioequivalence and safety of a novel fentanyl transdermal matrix system compared with a transdermal reservoir system

OBJECTIVES

Fentanyl is a potent synthetic opioid used for the management of chronic pain. A newer transdermal matrix system was developed and compared with a reservoir system used in the United States.

SETTING

An open-label, single-center, randomized, two-period crossover study was conducted to evaluate the bioequivalence of the transdermal matrix system to the transdermal reservoir system. Seventy-four subjects completed treatment with both the reservoir system (100 microg/h) and the matrix system (100 microg/h), each applied for 72 hours. After application of the first system, subjects completed a 9-day washout and then crossed over to receive the other system for another 72 hours.

MAIN OUTCOME MEASURE

Blood samples for the determination of serum fentanyl concentrations were taken in each treatment period for up to 120 hours following application.

RESULTS

The ratios of geometric means for maximum fentanyl concentration (Cmax) and area under the concentration-time curve (AUClast, and AUCinfinity) were 106 percent, 110 percent, and 110 percent, respectively. The 90% confidence intervals for the ratios of the geometric means were contained within the bioequivalence criteria of 80-125 percent. The matrix system adhered well to skin. Systemic and topical safety profiles were comparable between treatments.

CONCLUSIONS

The transdermal fentanyl matrix system adhered well, was well tolerated, and produced systemic exposures of fentanyl that were bioequivalent to the reservoir system.

[Pharmacokinetics of fentanyl during sevoflurane based general anesthesia in children]

The research is based on the analysis of 50 cases of anesthesia during reconstructive surgeries in children. The anesthesia was based on inhalation of sevolflurane and injection of fentanyl by the bolus infusion scheme. During the different stages of anesthesia the opioid concentration in plasma was measured. Analysis of hemodynamic parameters showed no statistically significant differences in changes in performance, indicating the steady flow of anesthesia. Infusion of fentanyl provided a smooth, gradual decrease in its concentration in plasma, while analgesia remained adequate. The combination of sevoflurane in a concentration of 1.3 MAC and infusion of fentanyl to a total dose 6 mkg/kg/h was effective in provisioning stable anesthesia in the given category of patients with surgical pathology.

[Educational efficacy of computer software showing the effect-site concentration of fentanyl in anesthesia training]

BACKGROUND

We investigated the efficacy of computer software showing the effect-site concentration of fentanyl in anesthesia training.

METHODS

All patients were randomly divided into the following three groups. Anesthesia management was performed with a pharmacokinetic simulation program by anesthesia residents with experience in using it for less than 3 months (P (+) group, n = 32). Anesthesia management was performed without a pharmacokinetic simulation program by anesthesia residents with experience in using it for less than two weeks (P (-) group, n = 25). Anesthesia management was performed without a pharmacokinetic simulation program by anesthesia residents with no experience in using it, under supervision of experienced anesthesiologists (C group, n = 22). We measured the effect-site concentration of fentanyl (Ce of fentanyl) at the end of surgery, intraoperative total doses of fentanyl and propofol, the time required from the end of operation to extubation, and frequency of analgesics required within 24 hours.

RESULTS

Total doses of fentanyl were significantly more in P (+) group than in other two groups. Ce of fentanyl were significantly more in P (+) group than in other two groups.

CONCLUSIONS

A pharmacokinetic simulation program is useful for anesthesia residents.

Modified surface coatings and their effect on drug adsorption within the extracorporeal life support circuit

A recently completed study quantified the percent of fentanyl or morphine sulfate lost to uncoated polyvinylchloride (PVC) tubing or to one of two hollow fiber oxygenators within the extracorporeal life support (ECLS) circuit. The results demonstrated the majority of drug loss was due to adsorption by the PVC tubing. The purpose of this study was to determine if a tubing coating process affects fentanyl or morphine Sulfate adsorption. The goal was to quantify fentanyl or morphine sulfate lost due to adhesion within surface modified tubing. The following surface modifications were studied: 1) Maquet Safeline (synthetic immobilized albumin); 2) Maquet Softline (a heparin free biopassive polymer); 3) Maquet Bioline (recombinant human albumin + heparin) (Maquet Cardiopulmonary AG, Hirrlingen, Germany); 4) Terumo X Coating (poly2methoxylacrylate)) (Terumo Cardiovascular Systems Corporation, Ann Arbor, MI); 5) Medtronic Carmeda (covalently bonded heparin); and 6) Medtronic Trillium (covalently bonded heparin) (Medtronic, Minneapolis, MN). A total of 36 individual circuits were built from the above six available modified surface coatings, for a total of six individual circuits of each coating type. Blood samples were drawn at 5 minutes, 120 minutes, and 360 minutes followed by High-Performance Liquid Chromatography to determine available circulating levels of either fentanyl or morphine sulfate. Fentanyl concentrations decreased to an average final available concentration of 35% (+/- 5%) within the 18 circuits. Morphine sulfate however, decreased to a final available concentration of 57% (+ 1%) in all Maquet tubing and the Medtronic Trillium tubing, while it decreased to a final concentration of 35% (+ 1%) in the Medtronic Carmeda coated tubing and in the Terumo X Coating tubing. Biocompatible ECLS circuit surface coatings affected drug-adsorption and availability. Further evaluation is necessary to understand the adsorptive loss of other drugs administered to our patients while on modified surface coated ECLS circuits.

Applying partially occluded fentanyl transdermal patches to manage pain in pediatric patients

Fentanyl transdermal patches (FTPs) have been used for many years in the treatment armamentarium for chronic pain. By design, FTPs release drug into the skin at a constant rate and thereby provide drug in a fashion similar to continuous intravenous infusion without the disadvantages of a venous catheter and the constant presence of an analgesia pump. Pediatric patients may require doses of FTP other than the five commercially available strengths. Application of a partial FTP allows for more flexibility in dosing. Yet, very little information is provided in the literature to suggest a procedure for applying partial FTP. A technique of using a partially occluded FTP is presented in an effort to encourage further study of this and perhaps other techniques.

The potential for mu-opioid receptor agonists to be anti-emetic in humans: a review of clinical data

In animal models of vomiting, mu-opioid (MOP, OP(3)) receptors mediate both emesis and anti-emesis. mu-receptors within the blood-brain barrier, mediating anti-emesis, are more rapidly accessible to lipid-soluble mu-opioid receptor agonists such as fentanyl than to morphine, and fentanyl has broad-spectrum anti-emetic effects in a number of species. Whether a similar situation exists in humans is not known. A search was performed for clinical studies comparing the emetic side effects of opioids administered peri-operatively in an attempt to identify differences between morphine and more lipid-soluble mu-receptor-selective agonists such as fentanyl. Overall, the evidence appears to suggest that fentanyl and other phenylpiperidines are associated with less nausea and vomiting than morphine, but not all studies support this, and fentanyl-like drugs are associated with nausea and vomiting per se. Good evidence, however, exists to show that fentanyl and alfentanil do not cause more nausea and vomiting than the ultra fast-acting remifentanil. Because remifentanil is cleared rapidly post-operatively, such trials suggest that the emetic side effects of fentanyl and alfentanil are minimal. The clinical evidence, although limited, is at least consistent with the possibility that central mu-opioid receptors may mediate anti-emesis in humans. It is possible that the role of mu-opioid agonists in anti-emesis may become clearer in the future as a result of the use of peripheral mu-opioid receptor antagonists.

Transdermal fentanyl: pharmacology and toxicology

OBJECTIVE

To evaluate the underlying pharmacology, safety, and misuse/abuse of transdermal fentanyl, one of the cornerstone pharmacotherapies for patients with chronic pain.

METHODS

Literature was identified through searches of Medline (PubMed) and several textbooks in the areas of pharmacology, toxicology, and pain management. A bibliographical review of articles identified by these searches was also performed. Search terms included combinations of the following: fentanyl, transdermal, patch, pharmacology, kinetics, toxicity, and poisoning. All pertinent clinical trials, retrospective studies, and case reports relevant to fentanyl pharmacology and transdermal fentanyl administered by any route and published in English were identified. Each was reviewed for data regarding the clinical pharmacology, abuse, misuse, and safety of transdermal fentanyl. Data from these studies and information from review articles and pharmaceutical prescribing information were included in this review.

RESULTS

Fentanyl is a high-potency opioid that has many uses in the treatment of both acute and chronic pain. Intentional or unintentional misuse, as well as abuse, may lead to significant clinical consequences, including death. Both the US Food and Drug Administration (FDA) and Health Canada have warned of potential pitfalls associated with transdermal fentanyl, although these have not been completely effective in preventing life-threatening adverse events and fatalities related to its inappropriate use.

CONCLUSIONS

Clinically consequential adverse effects may occur unexpectedly with normal use of transdermal fentanyl, or if misused or abused. Misuse and therapeutic error may be largely preventable through better education at all levels for both the prescriber and patient. The prevention of intentional misuse or abuse may require regulatory intervention.