Pharmacokinetics of fentanyl as determined by radioimmunoassay

Brain oxygen responses induced by opioids: focus on heroin, fentanyl, and their adulterants

Opioids are important tools for pain management, but abuse can result in serious health complications. Of these complications, respiratory depression that leads to brain hypoxia is the most dangerous, resulting in coma and death. Although all opioids at large doses induce brain hypoxia, danger is magnified with synthetic opioids such as fentanyl and structurally similar analogs. These drugs are highly potent, act rapidly, and are often not effectively treated by naloxone, the standard of care for opioid-induced respiratory depression. The goal of this review paper is to present and discuss brain oxygen responses induced by opioids, focusing on heroin and fentanyl. In contrast to studying drug-induced changes in respiratory activity, we used chronically implanted oxygen sensors coupled with high-speed amperometry to directly evaluate physiological and drug-induced fluctuations in brain oxygen levels in awake, freely moving rats. First, we provide an overview of brain oxygen responses to physiological stimuli and discuss the mechanisms regulating oxygen entry into brain tissue. Next, we present data on brain oxygen responses induced by heroin and fentanyl and review underlying mechanisms. These data allowed us to compare the effects of these drugs on brain oxygen in terms of their potency, time-dependent response pattern, and potentially lethal effect at high doses. Then, we present the interactive effects of opioids during polysubstance use (alcohol, ketamine, xylazine) on brain oxygenation. Finally, we consider factors that affect the therapeutic potential of naloxone, focusing on dosage, timing of drug delivery, and contamination of opioids by other neuroactive drugs. The latter issue is considered chiefly with respect to xylazine, which strongly potentiates the hypoxic effects of heroin and fentanyl. Although this work was done in rats, the data are human relevant and will aid in addressing the alarming rise in lethality associated with opioid misuse.

Evaluating the Pharmacokinetics of Fentanyl in the Brain Extracellular Fluid, Saliva, Urine, and Plasma of Newborns from Transplacental Exposure from Parturient Mothers Dosed with Epidural Fentanyl Utilizing PBPK Modeling

BACKGROUND AND OBJECTIVE

Fentanyl can mitigate the mother and newborn complications resulting from labor pain. However, fentanyl shows a narrow therapeutic index between its respiratory depressive and analgesic effects. Thus, prenatally acquired high fentanyl levels in the newborn brain extracellular fluid (bECF) may induce respiratory depression which requires therapeutic drug monitoring (TDM). TDM using saliva and urine in newborns can reduce the possibility of infections and distress associated with TDM using blood. The objective of this study was to develop  a physiologically based pharmacokinetic (PBPK) model to predict fentanyl concentrations in different newborn tissues due to intrauterine exposure.

METHODS

A fentanyl PBPK model in adults after intravenous and epidural administration was built, validated, and scaled to pregnancy and newborn populations. The dose that the newborn received transplacentally at birth was calculated using the pregnancy model. Then, the newborn bECF, saliva, plasma, and urine concentrations after such a dose were predicted using the newborn PBPK model.

RESULTS

After a maternal epidural dose of fentanyl 245 µg, the predicted newborn plasma and bECF levels were below the toxicity thresholds. Furthermore, the salivary threshold levels in newborns for fentanyl analgesic and respiratory depression effects were estimated to be 0.39 and 14.7-18.2 ng/ml, respectively.

CONCLUSION

The salivary TDM of fentanyl in newborns can be useful in newborns exposed to intrauterine exposure from parturient females dosed with epidural fentanyl. However, newborn-specific values of µ-opioid receptors IC50 for respiratory depression are needed.

Illicit Fentanyl Exposure Among Victims of Violence Treated at a Trauma Center

INTRODUCTION

Opioid overdoses and violent injury are leading causes of death in the United States, yet testing for novel opioids like fentanyl remains uncommon. The purpose of this investigation is to characterize a population of victims of violence who test positive for illicit fentanyl.

METHODS

Retrospective cohort study of patients treated at a level-one trauma center between January 31, 2019 and February 21, 2020. Data were extracted from the electronic medical record. Subjects were included if they had an encounter diagnosis for a violent or intentional injury, using the International Classification of Diseases, v10 (X92-Y09). We excluded patients who received licit fentanyl as a part of their care before testing. Those who tested positive for fentanyl exposure on our standard hospital urine drug screen were considered to have been exposed to illicit fentanyl. Those testing negative for fentanyl were considered controls.

RESULTS

Of the 1132 patients treated for intentional injuries during the study period, 366 were included in the study (32.3%). Of these, 133 (36.3%) subjects were exposed to illicit fentanyl prehospital. There were no demographic differences between cases and controls. Cases had a lower GCS voice score on arrival (median = 4, interquartile range [IQR] = 4-5 versus median = 5, IQR = 4-5, P = 0.02), higher rates of ventilator usage (32.3% versus 21.5%, P = 0.02), and more intensive care unit admissions (27.1% versus 12.0%, P = 0.005). More than half of cases tested negative for opiates (78/133, 58.6%). Cases had more trauma center encounters (26.3% had ≥2 visits versus 15.5%).

CONCLUSIONS

Exposure to illicit fentanyl was common among victims of violence in this single-center study. These patients are at increased risk of being admitted to intensive care units and repeated trauma center visits, suggesting fentanyl testing may help identify those who could benefit from violence prevention and substance abuse treatment.

Higher naloxone dosing in a quantitative systems pharmacology model that predicts naloxone-fentanyl competition at the opioid mu receptor level

Rapid resuscitation of an opioid overdose with naloxone, an opioid antagonist, is critical. We developed an opioid receptor quantitative systems pharmacology (QSP) model for evaluation of naloxone dosing. In this model we examined three opioid exposure levels that have been reported in the literature (25 ng/ml, 50 ng/ml, and 75 ng/ml of fentanyl). The model predicted naloxone-fentanyl interaction at the mu opioid receptor over a range of three naloxone doses. For a 2 mg intramuscular (IM) dose of naloxone at lower fentanyl exposure levels (25 ng/ml and 50 ng/ml), the time to decreasing mu receptor occupancy by fentanyl to 50% was 3 and 10 minutes, respectively. However, at a higher fentanyl exposure level (75 ng/ml), a dose of 2 mg IM of the naloxone failed to reduce mu receptor occupancy by fentanyl to 50%. In contrast, naloxone doses of 5 mg and 10 mg IM reduced mu receptor occupancy by fentanyl to 50% in 5.5 and 4 minutes respectively. These results suggest that the current doses of naloxone (2 mg IM or 4 mg intranasal (IN)) may be inadequate for rapid reversal of toxicity due to fentanyl exposure and that increasing the dose of naloxone is likely to improve outcomes.

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.

Intravenous hypnotic regimens in patients with liver disease; a review article

CONTEXT

The liver as an important organ in the body has many essential functions in physiological processes. One of the major activities of liver is drug metabolism. Hepatic dysfunction affecting hepatic physiological activities, especially drug metabolism can cause many problems during anesthesia and administration of different drugs to patients.

EVIDENCE ACQUISITION

Studies on hepatic disorders and hypnotic anesthetics prescribed in hepatic disorders were included in this review. For this purpose, reliable databases were used.

RESULTS

Anesthesia should be performed with caution in patients with hepatic dysfunction and drugs with long half-life should be avoided in these patients.

CONCLUSIONS

A review of the literature on the use of hypnotic drugs in patients with liver dysfunction showed that some hypnotic drugs used during anesthesia could be safely used in patients with impaired liver function. In these patients, certain drugs should be used with caution.

Methoxycarbonyl-etomidate: a novel rapidly metabolized and ultra-short-acting etomidate analogue that does not produce prolonged adrenocortical suppression

BACKGROUND

Etomidate is a rapidly acting sedative-hypnotic that provides hemodynamic stability. It causes prolonged suppression of adrenocortical steroid synthesis; therefore, its clinical utility and safety are limited. The authors describe the results of studies to define the pharmacology of (R)-3-methoxy-3-oxopropyl1-(1-phenylethyl)-1H-imidazole-5-carboxylate (MOC-etomidate), the first etomidate analogue designed to be susceptible to ultra-rapid metabolism.

METHODS

The gamma-aminobutyric acid type A receptor activities of MOC-etomidate and etomidate were compared by using electrophysiological techniques in human alpha1beta2gamma2l receptors. MOC-etomidate's hypnotic concentration was determined in tadpoles by using a loss of righting reflex assay. Its in vitro metabolic half-life was measured in human liver S9 fraction, and the resulting metabolite was provisionally identified by using high-performance liquid chromatography/mass spectrometry techniques. The hypnotic and hemodynamic actions of MOC-etomidate, etomidate, and propofol were defined in rats. The abilities of MOC-etomidate and etomidate to inhibit corticosterone production were assessed in rats.

RESULTS

MOC-etomidate potently enhanced gamma-aminobutyric acid type A receptor function and produced loss of righting reflex in tadpoles. Metabolism in human liver S9 fraction was first-order, with an in vitro half-life of 4.4 min versus more than 40 min for etomidate. MOC-etomidate's only detectable metabolite was a carboxylic acid. In rats, MOC-etomidate produced rapid loss of righting reflex that was extremely brief and caused minimal hemodynamic changes. Unlike etomidate, MOC-etomidate produced no adrenocortical suppression 30 min after administration.

CONCLUSIONS

MOC-etomidate is an etomidate analogue that retains etomidate's important favorable pharmacological properties. However, it is rapidly metabolized, ultra-short-acting, and does not produce prolonged adrenocortical suppression after bolus administration.

Genetic polymorphisms in the ABCB1 gene and the effects of fentanyl in Koreans

P-glycoprotein (PGP) is a polymorphic transporter encoded by the ABCB1 gene that contributes to the access of xenobiotics into the brain. There is no report on associations between genetic polymorphisms in ABCB1 and the clinical effects of fentanyl, although fentanyl may be a substrate of PGP. One hundred and twenty-six (126) unrelated Korean patients under spinal anesthesia with intravenous fentanyl (2.5 microg/kg) were recruited. Clinical effects (bispectral index, respiration rate, and need for oxygen supplementation) were monitored and these were compared between genotypes for three single nucleotide polymorphisms in ABCB1 (1236C>T, 2677G>T/A, and 3435C>T). The allele and genotype frequencies were similar to previous data from Asians; the three major haplotypes, TTT (30%), TGC (24%), and CGC (24%) were expected among nine known haplotypes. During the initial 10 min, there were differences in suppression of respiration rate by fentanyl among the three genotypes (P=0.0933 for 1236C>T; P=0.0941 for 2677G>A/T; P=0.0013 for 3435C>T, repeated-measures analysis of variance), but the differences in bispectral index among genotypes were not observed. Furthermore, patients carrying the linked 3435T and 2677T alleles showed a significant difference in the level of respiratory suppression (P=0.0056); those with genotypes susceptible to fentanyl (1236TT, 2677TT, and 3435TT) showed early (2-3 min) and profound suppression of respiration (65-73% of initial respiration rate) compared with other resistant genotypes (83-85% of initial respiration rate in 1236CC, 2677GG, and 3435CC). Although the need to supply oxygen was not significantly different between genotypes, there was a trend for increased demand by patients carrying both 1236T and 3435T alleles (P=0.0847). In conclusion, our results confirm ABCB1 genotype data for Koreans and suggest that analysis of ABCB1 polymorphisms may have clinical relevance to prevent respiratory suppression by intravenous fentanyl or to anticipate its clinical effects.

The effect of fentanyl on electrophysiologic recovery of CA 1 pyramidal cells from anoxia in the rat hippocampal slice

Fentanyl is widely used in conditions in which the brain is at risk of ischemic or anoxic injury. We evaluated the effect of fentanyl on anoxic injury to CA 1 pyramidal cells in the rat hippocampus. These neurons are extremely sensitive to anoxic injury and are densely populated with opioid receptors. We prepared hippocampal slices from adult Sprague-Dawley rats and evoked a postsynaptic population spike in the CA 1 pyramidal cell region by stimulating the Schaffer collateral pathway. The amplitude of this response was used to evaluate the effect of fentanyl on anoxic injury. Pretreatment with fentanyl (50 or 500 ng/mL) did not alter the amplitude of the CA 1 population spike before anoxia, nor did it alter the recovery of this response after 5,6, or 7 min of anoxia. After 5 min of anoxia, the population spike recovered to 76% of its preanoxic level in the control group and to 87% in the group treated with 500 ng/mL of fentanyl. After 6 min of anoxia, recovery was 45% in the control group, 57% in the group treated with 50 ng/mL of fentanyl, and 58% in the group treated with 500 ng/mL of fentanyl. After 7 min of anoxia, recovery was 5% in the control group and 4% in the group treated with 50 ng/mL of fentanyl. We conclude that fentanyl does not affect the recovery of the electrophysiological response in rat hippocampal neurons subjected to an anoxic insult.

IMPLICATIONS

Because fentanyl is used in large doses during surgical procedures in which the brain is at increased risk of ischemic or anoxic injury, it is important to determine its effect on such injury. Using the rat hippocampal slice model, we found fentanyl to be neither neurotoxic nor protective against anoxic injury to neurons when used in concentrations comparable to those produced in clinical practice.

Screening for drugs of abuse (II): Cannabinoids, lysergic acid diethylamide, buprenorphine, methadone, barbiturates, benzodiazepines and other drugs

Requirements for the provision of an efficient and reliable service for drugs of abuse screening in urine have been summarized in Part I of this review. The requirements included rapid turn-around times, good communications between requesting clinicians and the laboratory, and participation in quality assessment schemes. In addition, the need for checking/confirmation of positive results obtained for preliminary screening methods was stressed. This aspect of the service has assumed even greater importance with widespread use of dip-stick technology and the increasing number of reasons for which drug screening is performed. Many of these additional uses of drug screening have possible serious legal implications, for example, screening school pupils, professional footballers, parents involved in child custody cases, persons applying for renewal of a driving licence after disqualification for a drug-related offence, doctors seeking re-registration after removal for drug abuse, and checking for compliance with terms of probation orders; as well as pre-employment screening and work-place testing. In many cases these requests will be received from a general practitioner or drug clinic with no indication of the reason for which testing has been requested. This also raises the serious problems of a chain of custody, provision of two samples, stability of samples, and secure and lengthy storage of samples in the laboratory-samples may be requested by legal authorities several months after the initial testing. The need for confirmation of positive results is now widely accepted but it may be equally important to confirm unexpected negative results. Failure to detect the presence of maintenance drugs may lead to the patient being discharged from a drug treatment clinic and, if attendance at the clinic is one of the terms of continued employment, to dismissal. It seems likely that increasing abuse of drugs and the efforts of regulatory authorities to control this, will lead to the manufacture of more designer drugs. Production of substituted phenethylamines was facilitated by the drug makers' cook book, 'PIHKAL' (Phenethylamines I Have Known And Loved) by Dr Alexander Shulgin and Ann Shulgin, and production of substituted tryptamines is promised in their next book, TIHKAL. Looking to the future, laboratories will need to ensure that they can detect and quantitate an ever-increasing number of drugs and related substances. The question of confidence in results of drugs of abuse testing raised in 1993 by Watson has assumed even greater importance as a result of attention focused on the OJ Simpson trial in Los Angeles. Toxicological investigations are likely to be challenged more frequently in the future. Even if analyses have been performed by GC-MS, there is a need to establish the level of match between the spectrum of the unknown substance and a library spectrum which is considered acceptable for legal purposes. It will also be essential to ensure that computer libraries contain spectra for all substances likely to be encountered in drugs of abuse screening.

Direct effects of fentanyl on canine coronary artery rings

The potent opioid fentanyl, is commonly used as a general anesthetic for coronary artery bypass surgery. Experiments were designed to determine the direct effects of fentanyl on unstimulated coronary artery tissue. Isolated, endothelium denuded canine epicardial rings were suspended in physiologic tissue baths. Changes in tension were measured as the concentration of fentanyl was increased. Fentanyl caused increases in ring tension at concentrations of 10(-6)M-10(-4)M, then caused a decrease in tension at 10(-3) M. Calcium channel blockade by 10(-7)M nifedipine abolished all increases in contractile responses to fentanyl and prevented the relaxation in tension produced by fentanyl. The fentanyl dose-response curve was unchanged by opioid receptor blockade with 10(-6)M naloxone and by alpha and beta adrenoceptor blockade produced by 10(-6)M prazosin and 10(-6)M propranolol. Muscarinic blockade with 10(-6)M atropine and cyclooxygenase inhibition by 10(-6)M indomethacin attenuated the constrictor response to fentanyl. The opioids alfentanil, sufentanil, morphine, and naloxone all produced a dose-response similar to fentanyl that varied only in amplitude. These findings indicate that increasing concentration of the anesthetic opioid fentanyl can cause biphasic changes in basal canine epicardial coronary artery ring tension. These responses are calcium dependent and may be characteristics of other opioid agonists and antagonists.

Binding of fentanyl and pethidine to muscarinic receptors in rat brain

Symptoms similar to the central anticholinergic syndrome are often seen after high dose fentanyl anesthesia. Therefore, the binding of fentanyl, alfentanil, pethidine and morphine to opioid and muscarinic receptors was investigated in rat brain homogenate with [3H]naloxone and [3H]QNB as the radioligands, respectively. Both pethidine and fentanyl inhibited [3H]QNB binding with Ki values in the micromolar range. Alfentanil and morphine had no affinity for muscarinic receptors. The ratio of the Ki values for muscarinic receptors versus opioid receptors was 2.5 for pethidine and 88 for fentanyl. It is concluded that binding of fentanyl to muscarinic receptors is likely to occur during high-dose fentanyl anesthesia.

Concentration of fentanyl in colostrum after an analgesic dose

The purpose of this study was to measure the concentration of fentanyl in human colostrum after intravenous administration of an analgesic dose. Thirteen healthy women were given fentanyl 2 micrograms.kg-1 for analgesic supplementation during either Caesarean section or postpartum tubal ligation. Serum and colostrum were collected for 45 min, two, four, six, eight, and ten hours following administration of the drug. Radioimmunoassay showed that colostrum fentanyl concentrations were greatest at 45 min, the initial sampling time, reaching 0.40 +/- 0.059 ng.ml-1, but were virtually undetectable ten hours later. Fentanyl concentrations were always higher in colostrum than in serum. This concluded that with these small concentrations and fentanyl's low oral bioavailability, intravenous fentanyl analgesia may be used safely in breast-feeding women.

China White epidemic: an eastern United States emergency department experience

STUDY OBJECTIVE

The purpose of this study was to isolate significant clinical or demographic findings concerning overdose patients treated during a China White (3-methyl fentanyl) epidemic and compare them with data for all unintentional narcotic overdose patients during a 24-month period.

DESIGN

We reviewed charts from 85,246 patient visits to our emergency department during the 24-month period of January 1987 through December 1988 to study this narcotic epidemic. Data from the Allegheny County Coroner's Office pertaining to unintentional drug overdose deaths that occurred during this same period also were reviewed.

SETTING

The first outbreak of narcotic overdoses in the eastern United States involving China White occurred in Allegheny County, Pennsylvania, in 1988.

TYPE OF PARTICIPANTS

Patients were included if they met the criteria of a suspected unintentional narcotic overdose, but excluded if they were not given naloxone.

INTERVENTIONS

Emergency physicians became suspicious of China White use after an unusual increase in narcotic overdoses presenting to the ED coupled with "routine drug of abuse" screens negative for opiates despite dramatic patient responses to naloxone. In most of the cases in which specific testing was done, there were positive indicators of fentanyl derivatives. Investigations found China White present in street drugs and paraphernalia.

MEASUREMENTS AND MAIN RESULTS

A cluster was defined as a time period with a statistically significant increase in overdoses over the expected number for an interval of equal length. Although there were no significant clinical differences in case presentation during the 24-month period, there was a statistically significant 13-fold increase in overdoses during the September through November 1988 cluster (mean, 13 vs 0.95 per month, P less than .001 by Wilcoxon rank-sum test). A dramatic increase in unintentional drug overdose deaths occurred in the county during this cluster. A total of 18 fentanyl-positive unintentional drug overdose deaths, predominantly male (89%) and black (56%), with an age range of 19 to 44 years (mean, 34.9 years), were reported by the county coroner (13 during the cluster). Narcotic overdoses and unintentional drug overdose deaths declined sharply with confiscation of a clandestine China White laboratory.

CONCLUSIONS

China White was responsible for a dramatic rise in unintentional drug overdose deaths in Allegheny County in 1988. There were no significant clinical differences between China White overdose survivors and other unintentional narcotic overdose victims. Overdoses responsive to naloxone with inconsistent routine toxicologic screens may be due to a fentanyl analogue.

"Designer drugs"--a current perspective

Since the late 1970s, in an effort to quench the ever burgeoning appetite for pharmacological substances of abuse and to satiate their own need for profit, unscrupulous chemists have set up clandestine laboratories to produce and market new drugs for street sale. Using fairly common industrial chemicals, they have altered or modified preexisting controlled substances such as fentanyl, meperidine, mescaline, amphetamine, and phencyclidine, producing derivatives of these parent compounds that, up until 1986, were able to temporarily elude the guidelines of the Federal Controlled Substances Act due to their new and unique chemical structures. Unsuspecting users continue to use the drugs recreationally. This article will present a comprehensive review of these "Designer Drugs" looking at historical data, pharmacokinetics, treatment, abuse trends, and some of the more recent additions to the social pharmacopoeia.

Transdermal delivery of narcotic analgesics: pH, anatomical, and subject influences on cutaneous permeability of fentanyl and sufentanil

The permeation of fentanyl and sufentanil through cadaver skin membranes was investigated using in vitro diffusion cell techniques. Neither drug influenced the permeation of the other when they were concurrently applied to the skin membrane. With respect to transdermal delivery, short diffusion lag times of less than 0.5 hr were observed for each compound. Their permeation rates through heat-isolated epidermis and dermatomed (200- to 250-microns) skin sections were essentially the same. However, when the stratum corneum was removed by tape stripping, the respective permeability coefficients were increased greater than 30-fold, establishing the stratum corneum as the principal barrier to their skin permeation. Permeation was also studied as a function of pH. From pH 4 to pH 8 the permeability coefficients of both fentanyl and sufentanil, calculated from the total solution concentration regardless of ionization, increased exponentially. The free base is thus responsible for the relatively facile skin permeation of these drugs. Factoring of the independent permeability coefficients of the ionized and free-base forms was possible, with the latter being over two log orders larger than seen for the protonated species. Permeability coefficients of fentanyl and sufentanil through skin sections obtained from different cadavers varied four- to fivefold. Neither gender nor age was a flux-determining variable for either drug. The permeability coefficients of the drugs through skin sites as diverse as the sole of the foot, chest, thigh, and abdomen were remarkably similar. Their fluxes were sufficient for transdermal administration.

The safety of fentanyl use in the emergency department

Fentanyl citrate is a synthetic narcotic 1,000 times as potent as meperidine. It produces minimal hemodynamic effects and is characterized by a rapid onset of sedation and analgesia, a relatively short duration of action (approximately 30 to 40 minutes), and rapid reversal with opiate antagonists. These properties make fentanyl an ideal drug for emergency department use. The safety of fentanyl use in an adult ED population has not previously been studied. We retrospectively reviewed the charts of 841 patients who received fentanyl at the University of Cincinnati Center for Emergency Care between January 1985 and June 1988. The study population included 497 (59%) men and 344 (41%) women, with an average age of 33 years. The average dose of fentanyl was 180 micrograms (range, 25 to 1,400 micrograms). Six patients (1%) experienced mild side effects including nausea (one), emesis (two), urticaria (one), and pruritus (two). Nine patients (1%) developed more serious complications including six cases (0.7%) of respiratory depression and three cases (0.4%) of hypotension. Two of 183 patients (1%) who received midazolam and two of nine patients (22%) who received haloperidol developed respiratory depression. Four of the six patients with respiratory depression and two of the three patients with hypotension were intoxicated. All of the complications were transient, and none resulted in hospitalization. We conclude that fentanyl is a safe drug for use in the ED. To maximize safety, we recommend careful dosing and titration, close patient monitoring, and the availability of naloxone hydrochloride and resuscitation equipment.(ABSTRACT TRUNCATED AT 250 WORDS)

Attenuation of the hemodynamic responses to chest physical therapy

Chest physiotherapy (CPT) is a commonly used technique in mechanically ventilated critically ill patients. This study examines the hemodynamic and metabolic changes associated with CPT and measures the attenuation by two doses of intravenous fentanyl (1.5 micrograms/kg and 3.0 micrograms/kg) on these changes. Heart rate, systolic and mean blood pressures, cardiac output, oxygen consumption (VO2), and carbon dioxide production (VCO2) all increased during CPT. Decreases in arterial pH and VE and increases in PaCO2 were also observed. The higher, but not lower dose, of fentanyl significantly attenuated increases in blood pressure and heart rate during CPT and no substantial hemodynamic changes occurred once CPT had stopped. The increases in VO2 and VCO2 were not attenuated. Short acting narcotics attenuate the hemodynamic responses to stressful stimuli such as CPT.

Variability of fentanyl pharmacokinetics in man. Computer predicted plasma concentrations for three intravenous dosage regimens

The derived pharmacokinetic data for the intravenous administration of fentanyl obtained from seven previous studies were compared using computer simulation of predicted plasma concentrations following three intravenous dosage regimens. There was wide discrepancy between the reported calculated pharmacokinetic constants from the various studies, such that the volume of distribution ranged from 4.4 to 59.7 litres, estimates of terminal elimination half-life ranged from 141 to 853 minutes while total body clearance values ranged from 160 to 1530 ml/minute. The differences in predicted plasma concentrations were marked. The peak concentration following a bolus of 500 micrograms ranged from 8.4-113.6 ng/ml and took from 2.9 to 18.9 hours to fall to 0.5 ng/ml. The steady state plasma concentration reached with an infusion of 0.3 microgram/kg/minute varied from 12.2-119.9 ng/ml and the plateau level attained with a two-rate infusion (2.7 micrograms/kg/minute for 20 minutes then 0.3 micrograms/kg/minute) ranged from 10.6-50.8 ng/ml. The aim of descriptive pharmacokinetics is to allow the clinician to predict the plasma concentration achieved by a given dose and to facilitate dosage choice and adjustment. Recent interest has centred on the use of pharmacokinetics to calculate continuous intravenous infusion dosage regimens. The clinical application of current pharmacokinetic data for fentanyl is questionable.

Quantitative analysis of common anaesthetic agents

A summary of chromatographic (e.g. gas chromatography, high-performance liquid chromatography) and non-chromatographic (e.g. radioimmunoassay, enzyme-multiplied immunoassay) analytical techniques suitable for the quantitative analysis of the most popular inhalational (halothane, methoxyflurane, enflurane, isoflurane and nitrous oxide), intravenous (barbiturate, benzodiazepines, etomidate, althesin, morphine, fentanyl, alfentanil, sufentanil, droperidol and ketamine) general and amide-type local (lidocaine, mepivacaine, etidocaine and bupivacaine) anaesthetic agents and some of their metabolites, in biological material, is described. In the case of inhalational anaesthetics attention is also payed to pollution measurement and breath-to-breath monitoring.

Human pharmacokinetics of analgesics and methods for their determination in biological fluids

The main pharmacokinetic data of analgesics--biological half-lives, apparent volumes of distribution, total body clearances--obtained in humans, and their clinical relevance are summarized. Special emphasis has been given to the analytical methods used for the quantitative determination of these drugs in biological fluids.

Clinical pharmacokinetics of fentanyl and its newer derivatives

Fentanyl, a synthetic opiate with a (clinical) potency of 50 to 100 times that of morphine, was introduced into clinical practice in the early 1960s. Usually administered by single intravenous doses, it developed a reputation for having a short duration of action and it was assumed that this was a consequence of rapid removal from the body. However, as clinical experience increased, it was realised that administration of multiple doses or large doses during narcotic-based anaesthesia sometimes led to delayed recovery and prolonged respiratory depression, suggesting that the duration of action was limited by redistribution within the body rather than removal from the body. Recent developments in analytical techniques have allowed pharmacokinetic studies and these have confirmed this opinion; fentanyl is rightly regarded as having a redistribution-limited duration of action after single or infrequent doses (analogous to thiopentone). However, the magnitude of the pharmacokinetic constants reported for fentanyl are remarkably inconsistent even in healthy volunteers, for reasons apparently only explainable by assay differences. Hence, estimates of apparent volume of distribution (area) range from around 60L to over 300L, estimates of terminal half-life range from about 1.5 to 6 hours (15 hours in geriatric patients) and total body clearance ranges from 0.4 to over 1.5 L/min. Renal excretion accounts for up to 10% of the dose; the remainder of the clearance would appear to be predominantly hepatic, but with contributions from other tissues. Continued clinical developments of narcotic-based anaesthetic techniques have resulted in high doses of narcotic being used, with oxygen, as the sole anaesthetic agents. At present these techniques are usually based on fentanyl, and the technique is frequently called 'stress-free anaesthesia' because of the effects in obtunding the 'stress response' caused by surgery (elevation of plasma concentrations of cortisol, glucose, ADH, etc. in the intra- and post-operative period) and the lack of deleterious effects on the cardiovascular system.(ABSTRACT TRUNCATED AT 400 WORDS)

Opiate analgesia and its antagonism in dental event-related potentials: evidence for placebo antagonism

The analgesic effects of the synthetic opiate fentanyl citrate (0.1 mg) on subjective pain reports (SPR) and late-wave event-related potentials (ERP) recorded during painful dental stimulation were examined in human subjects. Such waves have been shown to reflect the contribution of cognitive variables, such as expectancy and belief, to perception. In addition, the study was intended to demonstrate a dose-related narcotic antagonism with injection of naloxone (1.2 or 0.4 mg) or normal saline (double-blind) following IV fentanyl administration. Fentanyl reduced both ERP waveform amplitudes and SPR as have previously studied analgesic agents, such as nitrous oxide, acupuncture, and aspirin. Naloxone injection reversed both ERP and SPR changes, but surprisingly, a reversal of narcotic analgesia equal to that of 0.4 mg naloxone was seen with saline injection. By chance, all subjects were health-science students or professionals who were knowledgeable in opiate pharmacology, and so placebo reversal was hypothesized. Alternatively, it was hypothesized that fentanyl cleared more rapidly than predicted, thus, producing apparent reveal. In a second experiment involving similarly knowledgeable subjects with identical procedures and testing intervals, subjects received 0.1 mg fentanyl, but no reversal injection. The fentanyl effect was constant across this time period. The data, thus, support the hypothesis where the subjects were knowledgeable in opiate pharmacology, was placebo opiate antagonism.

The assay of fentanyl and its metabolites in plasma of patients using gas chromatography with alkali flame ionisation detection and gas chromatography-mass spectrometry

Fentanyl was determined using gas chromatography (GC) and alkali flame ionisation detection (AFID), in the plasma of patients who had received a high single dose (up to 60 microgram/kg body weight). The relative standard deviation is 6% for 11 ng/ml while the calculated detection limit is 3.3 ng of fentanyl per 1 ml of plasma. The concentration of fentanyl in patients ranged from 40 to 3 ng/ml of plasma. The concentration of fentanyl in patients ranged from 40 to 3 ng/ml of plasma in the first hour after administration. In the plasma of patients treated with fentanyl two metabolites could be detected and identified using GC-AFID and GC-MS.

Neurolept anaesthesia for the renal transplant operation

Between October 1973 and December 1976, neurolept anesthesia was used in 176 consecutive renal transplantations carried out in 155 patients. For premedication, the combination either of droperidol, diazepam and atropine or of oxicon and scopolamine was used; the latter was found to be more effective. The induction agent was droperidol or thiomebumal sodium, the barbiturate being found to be preferable. For maintenance, nitrous oxide and fentanyl were employed. Pancuronium was given as a muscle relaxant. The fact that the patients belonged to a high-risk category as regards anesthesia was apparent from the frequent occurrence of abnormal features in the heart-lung radiographs (47%) and ECG (53%). As could be expected in uraemic patients, anaemia and hypertension were fairly common. Induction was followed by a marked fall in blood pressure in 30% of the patients. During anaesthesia, there was a drop in blood pressure of more than 30% of the initial value in 35% of the patients, usually associated with a blood loss. In the majority of cases the course the anaesthesia was uneventful. In four patients (2.3%), the onset of respiration was delayed and re-intubation was resorted to. One patient developed arrhythmia requiring treatment. There was no evidence of nephrotoxicity. The per- and postoperative mortality was nil. The findings in this series indicate that neurolept anaesthesia is suitable for renal transplant operation.

Fentanyl pharmacokinetics in awake volunteers

A single intravenous dose of fentanyl (either 2 or 4 micrograms/kg body weight) was given to 13 healthy, young volunteer subjects. Serum fentanyl concentration decreased in a triexponential pattern. The terminal half-times were 750 and 853 minutes, respectively. A three-compartment, open, mammillary model is proposed for fentanyl kinetics.

Serum levels of butorphanol by radioimmunoassay

A radioimmunassay was developed for the analysis of butorphanol in human serum. The procedure involves extraction of serum with hexane containing 2% isoamyl alcohol, followed by evaporative solvent removal and radioimmunoassay of the reconstituted residue. The antibody significantly cross-reacts with unidentified butorphanol metabolites but not with two known metabolites, hydroxybutorphanol and norbutorphanol. Extraction eliminated interference from the butorphanol metabolites normally present in serum. The antibody also cross-reacts with pentazocine and cyclazocine but not with morphine, hydromorphone, oxymorphine, codeine, methadone, and meperidine. Butorphanol tartrate was administered intravenously (2 mg) to normal male volunteers. Serum butorphanol levels declined biexponentially with an average terminal half-life of 2.7 hr. Enzymatic serum hydrolysis prior to extraction yielded additional butorphanol, indicating the presence of butorphanol conjugates. The specificity of the assay for butorphanol was confirmed by GLC--mass fragmentography.