Phencyclidine disposition after intravenous and oral doses

The blood-to-plasma ratio and predicted GABAA-binding affinity of designer benzodiazepines

PURPOSE

The number of benzodiazepines appearing as new psychoactive substances (NPS) is continually increasing. Information about the pharmacological parameters of these compounds is required to fully understand their potential effects and harms. One parameter that has yet to be described is the blood-to-plasma ratio. Knowledge of the pharmacodynamics of designer benzodiazepines is also important, and the use of quantitative structure-activity relationship (QSAR) modelling provides a fast and inexpensive method of predicting binding affinity to the GABA_A receptor.

METHODS

In this work, the blood-to-plasma ratios for six designer benzodiazepines (deschloroetizolam, diclazepam, etizolam, meclonazepam, phenazepam, and pyrazolam) were determined. A previously developed QSAR model was used to predict the binding affinity of nine designer benzodiazepines that have recently appeared.

RESULTS

Blood-to-plasma values ranged from 0.57 for phenazepam to 1.18 to pyrazolam. Four designer benzodiazepines appearing since 2017 (fluclotizolam, difludiazepam, flualprazolam, and clobromazolam) had predicted binding affinities to the GABA_A receptor that were greater than previously predicted binding affinities for other designer benzodiazepines.

CONCLUSIONS

This work highlights the diverse nature of the designer benzodiazepines and adds to our understanding of their pharmacology. The greater predicted binding affinities are a potential indication of the increasing potency of designer benzodiazepines appearing on the illicit drugs market.

In vitro and in vivo metabolism and detection of 3-HO-PCP, a synthetic phencyclidine, in human samples and pooled human hepatocytes using high resolution mass spectrometry

The new psychoactive substance (NPS) 3-HO-PCP, a phencyclidine (PCP) analog, was detected in a law enforcement seizure and in forensic samples in Denmark. Compared with PCP, 3-HO-PCP is known to be a more potent dissociative NPS, but no toxicokinetic investigations of 3-HO-PCP are yet available. Therefore, 3-HO-PCP was quantified in in vivo samples, and the following were investigated: plasma protein binding, in vitro and in vivo metabolites, and metabolic targets. All samples were separated by liquid chromatography and analyzed by mass spectrometry. The unbound fraction in plasma was determined as 0.72 ± 0.09. After in vitro incubation with pooled human hepatocytes, four metabolites were identified: a piperidine-hydroxyl-and piperidine ring opened N-dealkyl-COOH metabolite, and O-glucuronidated- and O-sulfate-conjugated metabolites. In vivo, depending on the sample and sample preparation, fewer metabolites were detected, as the O-sulfate-conjugated metabolite was not detected. The N-dealkylated-COOH metabolite was the main metabolite in the deconjugated urine sample. in vivo analytical targets in blood and brain samples were 3-HO-PCP and the O-glucuronidated metabolite, with 3-HO-PCP having the highest relative signal intensity. The drug levels of 3-HO-PCP quantified in blood were 0.013 and 0.095 mg/kg in a living and a deceased subject, respectively. The 3-HO-PCP concentrations in deconjugated urine in a sample from a living subject and in post-mortem brain were 7.8 and 0.16 mg/kg, respectively. The post mortem results showed a 1.5-fold higher concentration of 3-HO-PCP in the brain tissue than in the post mortem blood sample.

The origin of NMDA receptor hypofunction in schizophrenia

N-methyl-d-aspartate (NMDA) receptor (NMDAR) hypofunction plays a key role in pathophysiology of schizophrenia. Since NMDAR hypofunction has also been reported in autism, Alzheimer's disease and cognitive dementia, it is crucial to identify the location, timing, and mechanism of NMDAR hypofunction for schizophrenia for better understanding of disease etiology and for novel therapeutic intervention. In this review, we first discuss the shared underlying mechanisms of NMDAR hypofunction in NMDAR antagonist models and the anti-NMDAR autoantibody model of schizophrenia and suggest that NMDAR hypofunction could occur in GABAergic neurons in both models. Preclinical models using transgenic mice have shown that NMDAR hypofunction in cortical GABAergic neurons, in particular parvalbumin-positive fast-spiking interneurons, in the early postnatal period confers schizophrenia-related phenotypes. Recent studies suggest that NMDAR hypofunction can also occur in PV-positive GABAergic neurons with alterations of NMDAR-associated proteins, such as neuregulin/ErbB4, α7nAChR, and serine racemase. Furthermore, several environmental factors, such as oxidative stress, kynurenic acid and hypoxia, may also potentially elicit NMDAR hypofunction in GABAergic neurons in early postnatal period. Altogether, the studies discussed here support a central role for GABAergic abnormalities in the context of NMDAR hypofunction. We conclude by suggesting potential therapeutic strategies to improve the function of fast-spiking neurons.

DARK Classics in Chemical Neuroscience: Phencyclidine (PCP)

Phencyclidine (PCP, "angel dust", an arylcyclohexylamine) was the first non-natural, man-made illicit drug of abuse, and was coined 'the most dangerous drug in America" in the late 1970s (amidst sensational horror stories of the drug's effects); however, few other illicit drugs have had such a significant and broad impact on society-both good and bad. Originally developed as a new class of anesthetic, PCP-derived psychosis gave way to the PCP hypothesis of schizophrenia (later coined the NMDA receptor hypofunction hypothesis or the glutamate hypothesis of schizophrenia), which continues to drive therapeutic discovery for schizophrenia today. PCP also led to the discovery of ketamine (and a new paradigm for the treatment of major depression), as well as other illicit, designer drugs, such as methoxetamine (MXE) and a new wave of Internet commerce for illicit drugs (sold as research chemicals, or RCs). Furthermore, PCP is a significant contaminant/additive of many illegal drugs sold today, due to its ease of preparation by clandestine chemists. Here, we will review the history, importance, synthesis (both legal and clandestine), pharmacology, drug metabolism, and folklore of PCP, a true DARK classic in chemical neuroscience.

Phencyclidine-Based New Psychoactive Substances

The serendipitous discovery of phencyclidine (PCP) in 1956 sets the stage for significant research efforts that resulted in a plethora of analogs and derivatives designed to explore the biological effects of this class. PCP soon became the prototypical dissociative agent that eventually sneaked through the doors of clinical laboratories and became an established street drug. Estimations suggest that around 14 PCP analogs were identified as "street drugs" in the period between the 1960s and 1990s. Fast forward to the 2000s, and largely facilitated by advancements in electronic forms of communication made possible through the Internet, a variety of new PCP analogs began to attract the attention of communities interested in the collaborative exploration of these substances. Traditionally, as was the case with the first-generation analogs identified in previous decades, the substances explored represented compounds already known in the scientific literature. As the decade of the noughties unfolded, a number of new PCP-derived substances appeared on the scene, which included some analogs that have not been previously recorded in the published literature. The aim of this chapter is to present a brief introductory overview of substances that have materialized as PCP-derived new psychoactive substances (NPS) in recent years and their known pharmacology. Since N-methyl-D-aspartate receptor (NMDAR) antagonism is implicated in mediating the subjective and mind-altering effects of many dissociative drugs, additional data are included from other analogs not presently identified as NPS.

Customizing monoclonal antibodies for the treatment of methamphetamine abuse: current and future applications

Monoclonal antibody-based medications designed to bind (+)-methamphetamine (METH) with high affinity are among the newest approaches to the treatment of METH abuse and the associated medical complications. The potential clinical indications for these medications include treatment of overdose, reduction of drug dependence, and protection of vulnerable populations from METH-related complications. Research designed to discover and conduct preclinical and clinical testing of these antibodies suggests a scientific vision for how intact monoclonal antibody (mAb) (singular and plural) or small antigen-binding fragments of mAb could be engineered to optimize the proteins for specific therapeutic applications. In this review, we discuss keys to success in this development process including choosing predictors of specificity, efficacy, duration of action, and safety of the medications in disease models of acute and chronic drug abuse. We consider important aspects of METH-like hapten design and how hapten structural features influence specificity and affinity, with an example of a high-resolution X-ray crystal structure of a high-affinity antibody to demonstrate this structural relationship. Additionally, several prototype anti-METH mAb forms such as antigen-binding fragments and single-chain variable fragments are under development. Unique, customizable aspects of these fragments are presented with specific possible clinical indications. Finally, we discuss clinical trial progress of the first in kind anti-METH mAb, for which METH is the disease target instead of vulnerable central nervous system networks of receptors, binding sites, and neuronal connections.

Absorption, distribution, metabolism and excretion pharmacogenomics of drugs of abuse

Pharmacologic and toxic effects of xenobiotics, such as drugs of abuse, depend on the genotype and phenotype of an individual, and conversely on the isoenzymes involved in their metabolism and transport. The current knowledge of such isoenzymes of frequently abused therapeutics such as opioids (oxycodone, hydrocodone, methadone, fentanyl, buprenorphine, tramadol, heroin, morphine and codeine), anesthetics (γ-hydroxybutyric acid, propofol, ketamine and phencyclidine) and cognitive enhancers (methylphenidate and modafinil), and some important plant-derived hallucinogens (lysergide, salvinorin A, psilocybin and psilocin), as well as of nicotine in humans are summarized in this article. The isoenzymes (e.g., cytochrome P450, glucuronyltransferases, esterases and reductases) involved in the metabolism of drugs and some pharmacokinetic data are discussed. The relevance of such data is discussed for predicting possible interactions with other xenobiotics, understanding pharmacokinetic behavior and pharmacogenomic variations, assessing toxic risks, developing suitable toxicological analysis procedures, and finally for interpretating drug testing results.

Interpretation of oral fluid tests for drugs of abuse

Oral fluid testing for drugs of abuse offers significant advantages over urine as a test matrix. Collection can be performed under direct observation with reduced risk of adulteration and substitution. Drugs generally appear in oral fluid by passive diffusion from blood, but also may be deposited in the oral cavity during oral, smoked, and intranasal administration. Drug metabolites also can be detected in oral fluid. Unlike urine testing, there may be a close correspondence between drug and metabolite concentrations in oral fluid and in blood. Interpretation of oral fluid results for drugs of abuse should be an iterative process whereby one considers the test results in the context of program requirements and a broad scientific knowledge of the many factors involved in determining test outcome. This review delineates many of the chemical and metabolic processes involved in the disposition of drugs and metabolites in oral fluid that are important to the appropriate interpretation of oral fluid tests. Chemical, metabolic, kinetic, and analytic parameters are summarized for selected drugs of abuse, and general guidelines are offered for understanding the significance of oral fluid tests.

Effects of postnatal PCP treatment on locomotor behavior and striatal D2 receptor

Exposing the developing brain to the N-methyl-D-aspartate (NMDA) receptor antagonist phencyclidine (PCP) has been shown to cause deficits in neurobehavioral functions, particularly on learning and memory and seizure sensitivity. Besides acting as a noncompetitive NMDA antagonist, PCP at high doses is known to affect the dopaminergic system. The present study assessed the effect of postnatal PCP treatment on locomotor activity and striatal dopamine (DA) D(2) receptor. Male and female rat pups were injected intraperitoneally (i.p.) with one of three doses of PCP (1, 3 and 5 mg/kg) or saline from postnatal day (PD) 5 to PD 15. Control and PCP-treated rats were given a challenge dose of PCP (10 mg/kg) as adults, and their locomotor behaviors--locomotion, stereotypy and ataxia--were scored. Postnatal PCP treatment did not have any significant effect in either sex on any of the PCP-induced locomotor behavioral paradigms studied. Separate groups of male and female rats were treated daily with saline or PCP (5 mg/kg i.p.) from PD 5 to PD 15 and sacrificed either as juveniles (PD 21) or adults, and D(2) receptor binding was measured in their striata. Striatal D(2) receptor density in juvenile and adult male postnatal PCP-treated rats did not differ from saline-treated controls. Adult female PCP-treated rats showed a slight but significant reduction in the maximal binding of striatal D(2) receptors. There was no effect of postnatal PCP on striatal D(2) receptor binding in female juvenile rats. These results support the hypothesis that blocking the developing NMDA receptor minimally affects PCP-induced locomotor behavior and the striatal D(2) receptor.

1-[1-(2-Benzo[b]thiopheneyl)cyclohexyl]piperidine hydrochloride (BTCP) yields two active primary metabolites in vivo. Identification and quantification of BTCP primary metabolites in mice plasma, urine, and brain and their affinity for the neuronal dopamine transporter

1-[1-(2-Benzo[b]thiopheneyl)cyclohexyl]piperidine hydrochloride (BTCP) and cocaine bind to the neuronal dopamine transporter (DAT) to strongly inhibit dopamine (DA) reuptake. Although similar to acute administration, cocaine and BTCP produce sensitization and tolerance, respectively, on chronic administration. We previously found that liver microsomes produced two primary metabolites from BTCP with a high affinity for DAT. Because such metabolites, if produced in vivo, could account for the pharmacological difference with cocaine, it was important to compare BTCP biotransformations in vitro and in vivo. Therefore, we identified and quantified BTCP and primary metabolites in mice urine, plasma, and brain after acute i.p. administration. The low recovery yield suggest that BTCP might behave like its close analogue, phencyclidine, with long-term storage of metabolites. Two active metabolites found in vitro were found in mice brain with estimated half-life values similar to that of BTCP ( approximately 0.3 h). Although respective brain concentrations were 20 and 40 times lower than that of BTCP, their potency to displace in vivo [3H]BTCP bound to the DAT was 50 and 10 times higher, respectively, than that of BTCP. They could, therefore, contribute to the inhibition of DA transport and play an important role in BTCP pharmacology. They could also explain the differences between BTCP and cocaine on repeated administration.

Sweat testing for cocaine, codeine and metabolites by gas chromatography-mass spectrometry

Sweat testing for drugs of abuse provides a convenient and considerably less invasive method for monitoring drug exposure than blood or urine. Numerous devices have been developed for collection of sweat specimens. The most common device in current use is the PharmChek Sweat Patch, which usually is worn by an individual for five to ten days. This device has been utilized in several field trials comparing sweat test results to conventional urinalysis and the results have been favorable. Two new Fast Patch devices have been developed and tested that allow rapid collection of sweat specimens. The Hand-held Fast Patch was applied to the palm of the hand and the Torso Fast Patch was applied to the abdomen or the sides of the trunk (flanks) of volunteer subjects participating in a research study. Both patches employed heat-induced sweat stimulation and a larger cellulose pad for increased drug collection. Sweat specimens were collected for 30 min at various times following administration of cocaine or codeine in controlled dosing studies. After patch removal, the cellulose pad was extracted with sodium acetate buffer, followed by solid-phase extraction. Extracts were derivatized and analyzed by gas chromatography mass spectrometry (GC-MS) simultaneously for cocaine, codeine and metabolites. Cocaine and codeine were the primary analytes detected in sweat. Peak cocaine and codeine concentrations ranged from 33 to 3579 ng/patch and 11 to 1123 ng/patch, respectively, across all doses for the Hand-held Patch compared to 22-1463 ng/patch and 12-360 ng/patch, respectively, for the Torso Fast Patch. Peak concentrations generally occurred 4.5-24 h after dosing. Both drugs could be detected for at least 48 h after dosing. Considerably smaller concentrations of metabolites of cocaine and codeine were also present in some patches. Generally, concentrations of cocaine and codeine were higher in sweat specimens collected with the Hand-held Fast Patch than for the Torso Fast Patch. Drug concentrations were also considerably higher than those reported for the PharmChek Sweat Patch. The predominance of cocaine and codeine in sweat over metabolites is consistent with earlier studies of cocaine and codeine secretion in sweat. Multiple mechanisms appear to be operative in determining the amount of drug and metabolite secreted in sweat including passive diffusion from blood into sweat glands and outward transdermal migration of the drug. Additional important factors are the physico-chemical properties of the drug analyte, specific characteristics of the sweat collection device, site of sweat collection and, in this study, the application of heat to increase the amount of drug secreted.

Crystal structure of monoclonal 6B5 Fab complexed with phencyclidine

The crystal structure of monoclonal antibody (mAb) 6B5 Fab fragment complexed with 1-(1-phenylcyclohexyl)piperidine (PCP or phencyclidine) was determined at 2.2-A resolution. 6B5 was originally produced from a mouse immunized with a phencyclidine analogue hapten 5-[N-(1'phenylcyclohexyl)amino]pentanoic acid conjugated to bovine serum albumin. This mAb was selected for further study because of its high affinity (Kd = 2 x 10(-9) M/liter) for PCP and usefulness in reversing PCP-induced central nervous system toxicity in laboratory animals. The dominant feature of the 6B5 Fab.PCP complex is the deep binding site and hydrophobic nature of the interaction. The ligand binding pocket of 6B5 Fab has numerous aromatic side chains, as compared with other known Fab structures. The most notable feature of the binding site is a Trp at position 97H (H-chain), and the side chain of this residue appears to act as a hydrophobic umbrella on the ligand in the antigen binding pocket. There are only two other known Fabs found with a Trp at the 97H position in complementarity determining region (CDR) H3, but they do not play a major role in the interaction with their respective antigens; in both Fab TE33 and R6.5 the Trp 97H side chain is positioned away from the bound antigen. Comparison of the CDR residues of 6B5 with other Fab structures with similar CDR sizes and amino acid compositions reveals a number of important patterns of residue substitutions that appear to be critical for specific PCP ligand interactions.

Testing for drugs of abuse in saliva and sweat

The detection of marijuana, cocaine, opiates, amphetamines, benzodiazepines, barbiturates, PCP, alcohol and nicotine in saliva and sweat is reviewed, with emphasis on forensic applications. The short window of detection and lower levels of drugs present compared to levels found in urine limits the applications of sweat and saliva screening for drug use determination. However, these matrices may be applicable for use in driving while intoxicated and surveying populations for illicit drug use. Although not an illicit drug, the detection of ethanol is reviewed because of its importance in driving under the influence. Only with alcohol may saliva be used to estimate blood levels and the degree of impairment because of the problems with oral contamination and drug concentrations varying depending upon how the saliva is obtained. The detection of nicotine and cotinine (from smoking tobacco) is also covered because of its use in life insurance screening and surveying for passive exposure.

Incorporation of phencyclidine and its hydroxylated metabolites into hair

The incorporation of phencyclidine(PCP) and its three major hydroxylated metabolites, 1-(1-phenylcyclohexyl)-4-hydroxypiperidine(PCHP), trans-4-phenyl-4-piperidinocyclohexanol(t-PPC) and trans-1-phenyl-1-(4'-hydroxypiperidino)-4-cyclohexanol(t-PCPdiol) into rat hair was studied. Three Dark Agouti male rats were intraperitoneally administered with PCP x HCl at a dose of 0.5 or 1.0 mg/kg once a day for 10 successive days. The plasma samples were collected from 5 min to 360 min after injection of each drug. The hair samples were collected 28 days after the first administration. The hair samples were extracted with methanol-5N hydrochloric acid(20:1) for 1 h under sonication. The plasma and hair extracts were extracted or purified with Bond Elut Certify and the extracts were silylated for the determination of PCP and its metabolites by GC/MS. The plasma AUCs were as follows; PCP(2.03 microg x min/ml) > t-PCPdiol(0.60 microg x min/ml) > PCHP(0.11 microg x min/ml) > t-PPC (0.065 microg x min/ml), while the hair concentrations were as follows; PCP(7.51 ng/mg) > PCHP (1.22 ng/mg) > t-PPC(0.10 ng/mg) > t-PCPdiol (0.05 ng/mg). In view of their AUCs, the hair concentration of t-PCPdiol was quite low, whereas that of PCP was so high. PCHP, t-PPC or t-PCPdiol was separately administered as the parent drug to the rats, and then the plasma and hair samples were analyzed in the same manner as PCP experiments. The incorporation rates ([hair concentration]/[AUC]) of PCP and its hydroxylated metabolites were as follows; PCP(2.29) > PCHP(0.79) > t-PPC(0.36) > t-PCPdiol(0.32). These data suggest that the decrease in lipophilicity caused by the hydroxylation of PCP suppresses the incorporation of the metabolites from blood into hair and the hydroxylation on cyclohexane ring(t-PPC) induces the decrease of the drug incorporation into hair more than that on piperidine ring(PCHP).

Pharmacological potency and biodisposition of phencyclidine via inhalation exposure in mice

The purpose of the present study was to characterize the pharmacological effects and biodisposition of phencyclidine (PCP) following inhalation exposure to mice. Results from these studies indicate that PCP was easily volatilized when heated in a glass pipe. Volatilization was efficient with no significant formation of pyrolytic products. Exposure to the volatilized PCP resulted in a dose-dependent impairment in motor performance in both the rotorod and inverted-screen tests. PCP was equally effective in disrupting performance on the inverted-screen and rotorod with ED50 values corresponding to the volatilization of 10.7 and 13.2 mumol, respectively. The time courses were comparable to those produced following intravenous (i.v.) administration of PCP. In order to determine the dose of drug absorbed by inhalation, mice were exposed to [3H]-PCP. The ED50 values of PCP following i.v. administration were 4.1 and 6.2 mumol/kg in the inverted screen and rotorod, respectively. The biodisposition of PCP following inhalation exposure was similar to that after i.v. injections. At doses that produced approximately 50% of the maximum motor impairment by either administration route, higher ratios of the total drug equivalents were found following i.v. injection than that after inhalation, with the brain/plasma ratios of 1.3 +/- 0.2 versus 0.58 +/- 0.02, and brain/body ratios 0.59 +/- 0.06 versus 0.35 +/- 0.1 for i.v. and inhalation, respectively. However, the brain/plasma ratios of the concentrations of PCP were similar, 1.1 versus 0.9. The body concentration of PCP equivalents that produced 50% of the maximum effect after inhalation was 4.7 +/- 0.6 mumol/kg. These results indicate that inhalation of PCP produces a similar pharmacological profile to that of i.v. administration and suggest that the drug is equipotent by these two administrations routes. Moreover, these findings are consistent with the observation that smoking is becoming the most common route of administration among drug users.

Simple and sensitive detection of phencyclidine in body fluids by gas chromatography with surface ionization detection

Phencyclidine (PCP) can be detected in body fluids with very high sensitivity by gas chromatography (GC) with surface ionization detection (SID) using pethidine as internal standard. PCP was extracted with Sep-Pak C18 cartridges from whole blood and urine samples, which gave clean extracts. The calibration curve for spiked whole blood was linear in the range 1.25-20 ng/ml. The detection limit of PCP was approximately 15 pg on-column (0.75 ng/ml sample), which was much lower than by GC-nitrogen phosphorus detection. The recovery of PCP and pethidine from spiked whole blood or urine samples was above 85%. This method seems very useful for the determination of PCP in forensic and clinical toxicology.

Saliva testing for drugs of abuse

Saliva testing for drugs of abuse can provide both qualitative and quantitative information on the drug status of an individual undergoing testing. Self-administration by the oral, intranasal, and smoking routes often produces "shallow depots" of drug that contaminate the oral cavity. This depot produces elevated drug concentrations that can be detected for several hours. Thereafter, saliva drug concentrations generally reflect the free fraction of drug in blood. Also, many drugs are weak bases and saliva concentrations may be highly dependent upon pH conditions. These factors lead to highly variable S/P ratios for many of the drugs of abuse. Table 3 provides a compilation of experimental and theoretical S/P (total) ratios determined for drugs of abuse. Estimations of the theoretical S/P (total) ratios for acidic and basic drugs were based on the Henderson-Hasselbalch equation. Saliva pH was assumed to be 6.8 unless reported otherwise by the investigators. Generally, there was a high correlation of saliva drug concentrations with plasma, especially when oral contamination was eliminated. Assay methodology varied considerably, indicating that saliva assays could be readily developed from existing methodology. There are many potential applications for saliva testing for drugs of abuse. Table 4 lists several general areas in which information from saliva testing would be useful. Clearly, saliva drug tests can reveal the presence of a pharmacologically active drug in an individual at the time of testing. Significant correlations have been found between saliva concentrations of drugs of abuse and behavioral and physiological effects. Results indicate that saliva testing can provide valuable information in diagnostics, treatment, and forensic investigations of individuals suspected of drug abuse. It is expected that saliva testing for drugs of abuse will develop over the next decade into a mature science with substantial new applications.

"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.

Modification of phencyclidine intoxification and biodisposition by charcoal and other treatments

Studies were conducted to determine whether single or combination treatments of charcoal, paraffin, cholestyramine, and/or ammonium chloride (NH4Cl), would alter the rotarod-measured motor dysfunction induced by 10 to 90 mg/kg of phencyclidine (PCP). Additionally, the effect of NH4Cl/charcoal treatment of the biodisposition of 50 mg/kg PCP was evaluated in order to assess whether amelioration of behavioral effects could be correlated to alterations in brain levels, plasma levels, and/or the renal clearance of PCP and metabolites. NH4Cl/charcoal treatment proved more effective at reducing intoxication than either treatment singly, though effectiveness was reduced by larger doses of PCP. NH4Cl/charcoal treatment reduced intoxification by 40, 16, and 21% at PCP doses of 10, 25, and 50 mg/kg. However, the reduction in motor dysfunction observed at 25 and 50 mg/kg PCP was greater than the sum of the individual treatments. In contrast, the effect of combined NH4Cl and charcoal treatment on the biodisposition of 50 mg/kg PCP is not synergistic, but appears instead to be due simply to the additive effects of the individual treatments. Thus the amelioration of PCP intoxication cannot be fully explained by alterations in PCP biodisposition.

Measurement of the amino acid metabolite of phencyclidine by selected ion monitoring

A technique is described for the extraction and quantitation of the pentanoic acid metabolite of phencyclidine by gas chromatography/mass spectrometry. This compound was measured in urine samples from asymptomatic pregnant patients who used phencyclidine (PCP) and their neonates. The technique is sensitive to 25 ng ml-1 urine and standard curves were linear at 25-2000 ng ml-1. Levels in samples from asymptomatic patients were 27-1388 ng ml-1. Results suggest that the pentanoic acid metabolite could be considered as a screening marker for occasional PCP use.

Biotransformation of phencyclidine

PCP is metabolized extensively in the body via a variety of metabolic routes. Biotransformation is a major mechanism of PCP elimination in humans and termination of PCP action in mice. In general, PCP metabolites are less active pharmacologically than PCP itself. Primary metabolism involves hydroxylation of the alicyclic rings at several carbon atoms by cytochrome P-450-mediated monooxygenase. Hydroxylation of the aromatic ring seems to be less likely and has not been conclusively demonstrated. Hydroxylation of PCP at carbon 2 of the piperidine ring to form the unstable carbinolamine leads to formation of a series of polar, open-ring compounds. Monohydroxylated metabolites are conjugated with glucuronic or sulfuric acid, or are further hydroxylated to dihydroxy derivatives that can also be subject to conjugation. Formation of highly reactive electrophilic metabolites of PCP have been demonstrated in vitro in microsomal preparations. Covalent modification of tissue macromolecules by reactive intermediates can be responsible for suicide inactivation of cytochrome P-450 and can possibly mediate some long-term toxic effects of PCP. PCP inhaled by cigarette smoking is metabolized via similar routes. About 50% of the PCP in cigarette smoke is converted to PC, a major product of thermal degradation of PCP. PC and its hydroxylated and conjugated metabolites appear to contribute little to the pharmacology or acute toxicity of PCP.

Species differences in the in vitro metabolism of phencyclidine

The metabolism of 1-(1-phenylcyclohexyl)-piperidine (phencyclidine or PCP) by liver preparations from cat, monkey, rabbit and rat has been studied. 4-Phenyl-4-piperidinocyclohexanol (I), 1-1-phenylcyclohexyl-4-hydroxy-piperidine (II), N-(5-hydroxypentyl)-1-phenylcyclohexylamine (IX) and 5-(1-phenylcyclohexylamino)-valeric acid (X) were found in all species, but liver preparations of rat and rabbit were much more active than those of cat or monkey in metabolizing PCP. Only rabbit produced 4-(4'-hydroxypiperidino)-4-phenylcyclohexanol (III) in amounts detectable by g.l.c. Mass balance calculations of PCP, I, II, III, IX and X in the cat, monkey and rat indicate that other metabolic pathways not measured in this study are operative.