Percutaneous Absorption of Lorazepam, Diphenhydramine Hydrochloride, and Haloperidol from ABH Gel

The objective of this project was to study the percutaneous absorption of lorazepam, diphenhydramine hydrochloride, and haloperidol from a topical Pluronic lecithin organogel, also known as ABH gel, across the porcine ear skin and verify its suitability for topical application. ABH gel was prepared using lecithin in isopropyl palmitate solution (1:1) as an oil phase and 20% w/v Poloxamer 407 solution as an aqueous phase. The gel was characterized for pH, viscosity, drug content, and thermal behavior. A robust high-performance liquid chromatography method was developed and validated for simultaneous analysis of lorazepam, diphenhydramine hydrochloride, and haloperidol. The percutaneous absorption of lorazepam, diphenhydramine hydrochloride, and haloperidol from ABH gel was carried out using Franz cells across the Strat-M membrane and pig ear skin. The pH of ABH gel was found to be 5.66 ± 0.13. The retention time of diphenhydramine hydrochloride, haloperidol, and lorazepam was found to be 5.2 minutes, 7.8 minutes, and 18.9 minutes, respectively. The ABH gel was found to be stable for up to 30 days. Theoretical steady state plasma concentrations (CSS) of diphenhydramine hydrochloride, haloperidol, and lorazepam calculated from flux values were found to be 1.6 ng/mL, 0.13 ng/mL, and 2.30 ng/mL, respectively. The theoretical CSS of diphenhydramine hydrochloride, haloperidol, and lorazepam were much lower than required therapeutic concentrations for antiemetic activity to relieve chemotherapy-induced nausea and vomiting. From the percutaneous absorption data, it was evident that ABH gel failed to achieve required systemic levels of lorazepam, diphenhydramine hydrochloride, and haloperidol following topical application.

Comparison of lorazepam [7-chloro-5-(2-chlorophenyl)-1,3-dihydro-3-hydroxy-2H-1,4-benzodiazepin-2-one] occupancy of rat brain gamma-aminobutyric acid(A) receptors measured using in vivo [3H]flumazenil (8-fluoro 5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylic acid ethyl ester) binding and [11C]flumazenil micro-positron emission tomography

The occupancy by lorazepam of the benzodiazepine binding site of rat brain GABA(A) receptors was compared when measured using either in vivo binding of [(3)H]flumazenil (8-fluoro 5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylic acid ethyl ester) in terminal studies or [(11)C]flumazenil binding in anesthetized animals assessed using a small animal positron emission tomography (PET) scanner (micro-PET). In addition, as a bridging study, lorazepam occupancy was measured using [(3)H]flumazenil in vivo binding in rats anesthetized and dosed under micro-PET conditions. Plasma lorazepam concentrations were also determined, and for each occupancy method, the concentration required to produce 50% occupancy (EC(50)) was calculated because this parameter is independent of the route of lorazepam administration. For the in vivo binding assay, lorazepam was dosed orally (0.1-10 mg/kg), whereas for the micro-PET study, lorazepam was given via the i.v. route as a low dose (0.75 mg/kg bolus) and then a high dose (0.5 mg/kg bolus then 0.2 mg/ml infusion). The lorazepam plasma EC(50) in the [(11)C]flumazenil micro-PET study was 96 ng/ml [95% confidence intervals (CIs) = 74-124 ng/ml], which was very similar to the [(3)H]flumazenil micro-PET simulation study (94 ng/ml; 95% CI = 63-139 ng/ml), which in turn was comparable with the [(3)H]flumazenil in vivo binding study (134 ng/ml; 95% CI = 119-151 ng/ml). These data clearly show that despite the differences in dosing (i.v. in anesthetized versus orally in conscious rats) and detection (in vivo dynamic PET images versus ex vivo measurements in filtered and washed brain homogenates), [(11)C]flumazenil micro-PET produces results similar to [(3)H]flumazenil in vivo binding.

PET imaging of dopamine D2 receptors during chronic cocaine self-administration in monkeys

Dopamine neurotransmission is associated with high susceptibility to cocaine abuse. Positron emission tomography was used in 12 rhesus macaques to determine if dopamine D2 receptor availability was associated with the rate of cocaine reinforcement, and to study changes in brain dopaminergic function during maintenance of and abstinence from cocaine. Baseline D2 receptor availability was negatively correlated with rates of cocaine self-administration. D2 receptor availability decreased by 15-20% within 1 week of initiating self-administration and remained reduced by approximately 20% during 1 year of exposure. Long-term reductions in D2 receptor availability were observed, with decreases persisting for up to 1 year of abstinence in some monkeys. These data provide evidence for a predisposition to self-administer cocaine based on D2 receptor availability, and demonstrate that the brain dopamine system responds rapidly following cocaine exposure. Individual differences in the rate of recovery of D2 receptor function during abstinence were noted.

Glucuronidation enzymes, genes and psychiatry

The phase I cytochrome P450 (CYP) isoenzymes have received substantial attention in the pharmacogenetic literature. Researchers are beginning to examine the role of the phase II UDP-glucuronosyltransferase (UGT) enzymes, which produce products that are more water-soluble, less toxic and more readily excreted than the parent compounds. Several reasons may have contributed to neglect of UGTs (compared to CYPs) including: (1) the overlapping activity of UGTs and lack of selective probes; (2) the complexity of the glucuronidation cycle; and (3) the difficulty in developing analytic methods to measure glucuronides. Current CYP knowledge is used as a model to predict advances in UGT knowledge. At least 24 different UGT human genes have been identified and are classified in two families (UGT1 and UGT2) based on sequence homology. The UGT1A subfamily (genes located on chromosome 2) glucuronidates bilirubin, thyroid hormones, and some medications. UGT1A4 metabolizes tricyclic antidepressants and some antipsychotics. The UGT2B subfamily (genes located on chromosome 6) glucuronidates sexual steroids and bile acids. Oxazepam and lorazepam are mainly metabolized by glucuronidation. Anti-epileptics with mood-stabilizing properties are frequently metabolized by UGTs. Opioid and nicotine addiction may also be influenced by glucuronidation. Glucuronidation of serotonin may be important during fetal development. UGTs appear to be in small concentrations in brain tissue (and higher concentrations at brain capillaries). However, UGTs may be localized in certain brain areas to provide a neuroprotective function. This review illustrates the importance of glucuronidation and the implications for psychiatry.

Comparative pharmacokinetics and pharmacodynamics of lorazepam, alprazolam and diazepam

The contribution of differential absorption-distribution pharmacokinetics to drug activity can be partially determined by comparing simultaneous estimates of drug serum level with pharmacodynamic effects. In the present paper we have contrasted the effects of clinically equipotent doses of lorazepam, alprazolam, and diazepam on the performance of tracking and digit symbol substitution tasks. Eight young males were tested for 12 h after ingesting the drug. The three benzodiazepines and placebo were administered to each subject according to a balanced double-blind Latin square design. A model is presented that describes the relationship between drug concentration and the degree of impairment across time after the final peak effect. Exponential rate constants were determined for each drug using a Marquardt nonlinear fit of the pooled data. Basically, the constants relate offset serum drug values to the impairment curves at a time when serum-brain equilibrium is assumed to have occurred. The values indicate markedly rapid acute tolerance for alprazolam and diazepam but relatively little acute tolerance for lorazepam. Whether these constants reflect adaptation or differential association-dissociation receptor rate constants cannot be determined, but they do highlight the need to consider receptor kinetics as an important factor in benzodiazepine pharmacodynamics.

Comparison of the rates of hydrolysis of lorazepam-glucuronide, oxazepam-glucuronide and tamazepam-glucuronide catalyzed by E. coli beta-D-glucuronidase using the on-line benzodiazepine screening immunoassay on the Roche/Hitachi 917 analyzer

The catalytic rates of hydrolysis of lorazepam-glucuronide, oxazepam-glucuronide, and temazepam-glucuronide when catalyzed by E. Coli. beta-glucuronidase both in phosphate buffer and buffered drug-free urine were compared as well as the pH dependence of enzyme activity. In 50 mM phosphate buffer pH 6.4, lorazepam-glucuronide has the highest turnover rate of 3.7 s(-1) with an associated Km of about 100 microM, followed by oxazepam-glucuronide, which has a turnover rate of 2.4 s(-1) with an associated Km of 60 microM. Temazepam-glucuronide has the lowest rate of 0.94 s(-1) with an associated Km of 34 microM. In buffered drug-free urine, a similar trend was observed. In addition, an optimal pH for beta-glucuronidase was determined to be between 6 and 7 when the enzyme hydrolyzes the benzodiazepine conjugates in buffered drug-free urine. Effects of temperature and incubation time were also examined. It can be concluded that the electron donating or withdrawing of the individual benzodiazepine structure may play an important role in the reactivity of the lorazepam-glucuronide, oxazepam-glucuronide and temazepam-glucuronide catalyzed by beta-glucuronidase. This is consistent with other observations made for monosubstituted phenyl-beta-glucuronides by Wang et al. (1).

Identification of lorazepam and sildenafil as examples for the application of LC/ionspray-MS and MS-MS with mass spectra library searching in forensic toxicology

A mass spectra (MS) library using in-source collision induced dissociation (ESI-CID) as well as a tandem-mass spectra (MS-MS) library with product ion spectra of drugs has recently been developed with a triple-quadrupole ionspray mass spectrometer [1,2]. For the ESI-CID MS library, single-quadrupole mode and for the MS-MS library triple-quadrupole mode have been used. These mass spectra libraries were applied successfully for the general-unknown screening for drugs and metabolites in serum and urine with liquid-chromatography-mass spectrometry (LC-MS) using a PE/SCIEX API 365 with a turboionspray source. As examples, the identification of lorazepam and lorazepam-glucuronide in a serum extract and the identification of sildenafil and alkyloxidated sildenafil in urine are presented here.

Inhibitory effect of azole antifungal agents on the glucuronidation of lorazepam using rabbit liver microsomes in vitro

Azole antifungal agents (azoles) have inhibitory effects on the cytochrome P450. However, the effect of azoles on conjugative metabolism has not been given much attention. Lorazepam (LZP), a benzodiazepine sedative agent, is known to be metabolized by uridine 5'-diphosphate (UDP)-glucuronyltransferase. Herein we report investigation of the effect of azoles on the enzyme-kinetics of glucuronidation of lorazepam using rabbit liver microsomes in vitro. The Km and Vmax for LZP glucuronidation were determined to be 0.26+/-0.08 mM and 1.25+/-0.21 nmol/min/mg protein, respectively, when evaluated in the presence of a detergent 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS) (0.8 mg/mg protein). Azoles fluconazole, miconazole, and ketoconazole competitively inhibited the glucuronidation of LZP, with Ki values of 7.17+/-4.78 mM, 0.17+/-0.08 mM, and 0.092+/-0.026 mM, respectively. These results are comparable to the previously reported Ki values of azoles with zidovudine (AZT) glucuronidation (1.4, 0.18, and 0.08 mM for fluconazole, miconazole, and ketoconazole, respectively) [Sampol et al., Br. J. Clin. Pharmacol., 40, 83-86, 1995]. Therefore, in order to avoid possible side effects of LZP, the concomitant administration of LZP and azoles should be carefully evaluated.

Stereoselective allosteric binding interaction on human serum albumin between ibuprofen and lorazepam acetate

The effect of ibuprofen enantiomers on the stereoselective binding of 3-acyloxy-1,4-benzodiazepines to human serum albumin (HSA) was studied using both native and Sepharose-immobilized protein. (S)-Lorazepam acetate exhibited considerably enhanced binding, especially in the presence of (+)-(S)-ibuprofen. The phenomenon is an indication of cooperative allosteric interaction between different binding sites during multiple cobinding of two ligands.

Simultaneous extraction of selected benzodiazepines and benzodiazepine-glucuronides from urine by immunoadsorption

A rapid and selective cleanup procedure based on immunoadsorption is described for the simultaneous extraction of diazepam and its free or glucuronidated metabolites nordiazepam, temazepam, and oxazepam from urine. The method can also be used for the extraction of lorazepam and lorazepam-glucuronide. Because the samples do not have to be hydrolyzed before extraction, valuable information is preserved. With the exception of lorazepam-glucuronide, recoveries between 86 and 100% were obtained at spiking levels up to 200 ng of benzodiazepine or glucuronide per milliliter of urine. Using methanol/water (90:10, v/v) as an eluent, the immunoadsorber could be used at least 20 times. High-performance liquid chromatograms of urine samples from patients receiving low therapeutic dosages of diazepam or lorazepam are shown to demonstrate the high purity of the extracts.

Effects of lormetazepam on glycemia and serum lipids in hyperlipidemic rats

Lormetazepam (N-methyllorazepam) administered intraperitoneally to rats rendered hyperlipidemic by Triton WR-1339 induced an elevation of blood glucose level at all investigated doses. It brought about significant reduction of serum total lipids, total cholesterol and triglycerides. The dose-response relationship was bell-shaped. However, it presented two peaks, differing from the responses to other benzodiazepines (BZD) which were characterized by only one peak.

Progesterone: does it affect response to drug?

This article presents an overview of the gamma-aminobutyric acid (GABA)-benzodiazepine receptor complex (GBRC) and its in vitro modulation by THP, a metabolite of progesterone, as well as the results of a single-dose study of progesterone and triazolam in 16 post-menopausal women. The study results indicate that a 300 mg oral dose of progesterone administered 2.5 hours prior to a challenge dose of triazolam significantly increases sensitivity to triazolam: concentration values required for 50 percent of maximum effect (EC50) decreased by 20 to 32 percent after pre-treatment with progesterone. These data support the In vitro findings that THP enhances binding of benzodiazepines to the GBRC. The full clinical implications of these data, including extensions to other steroids, need to be explored.

Solubilized benzodiazepine receptors for use in receptor assays

In the development of non-radioactive receptor assays for benzodiazepines, employing fluorescent ligands, it was observed that the fluorescence measurements were hampered by the background fluorescence of the receptor preparation. This receptor preparation is a brain tissue homogenate in which the benzodiazepine receptors are membrane-bound. To minimize the influence of the receptor material on the fluorescence detection, the benzodiazepine receptors were solubilized with 0.5% sodium deoxycholate. The binding characteristics of the receptors were examined after solubilization and compared with membrane-bound receptors. The Kd and Bmax values for membrane-bound receptors were 1.20 nM and 1.01 pM mg-1 protein and for solubilized receptors they were 4.1 nM and 0.54 pM mg-1 protein respectively. Inhibition curves with the benzodiazepine antagonist flumazenil and the agonist lorazepam revealed that their affinities for the solubilized receptor as compared to the membrane-bound receptor were also reduced from 0.67 nM to 3.2 nM and from 1.49 nM to 8.4 nM respectively. The detection limits for the two benzodiazepines, however, were not affected by the solubilization. Furthermore, three different methods to separate the fraction of free labelled ligand and the fraction bound to the solubilized receptor were compared, namely polyethylene glycol precipitation/filtration, ion exchange filtration and charcoal adsorption. Polyethylene glycol precipitation/filtration gave the highest yield for the bound fraction and the best reproducibility.

Changes in liver drug glucuronidation during cholestasis are non predictable

Liver microsomal glucuronidation of acetaminophen, chloramphenicol, salicylic acid, lorazepam, p-nitrophenol and morphine were measured in 8 days bile duct ligated rats. Compared to normals, cholestatic rats showed a decrease of 31% for p-nitrophenol glucuronidation; salicylic acid glucuronidation increased 281%; acetaminophen glucuronidation increased 38% while morphine, chloramphenicol and lorazepam values were similar to controls. We concluded that cholestasis produces non predictable changes on liver drug glucuronidation pathways.

Inhibition of acetaminophen and lorazepam glucuronidation in vitro by probenecid

The effect of probenecid on glucuronidation of acetaminophen and lorazepam in hepatic microsomes from various species was studied to see if in vitro results were consistent with previous in vivo observations. Mouse, rat, and human microsomes were incubated with acetaminophen and probenecid while monkey microsomes were incubated with lorazepam and probenecid. Glucuronidation rates in all species varied with substrate, protein, and detergent concentrations. Mice exhibited faster rates of glucuronidation than rats or humans. All species showed inhibition of glucuronidation of acetaminophen or lorazepam when probenecid was added. Analysis suggested competitive inhibition. Thus, in vitro studies support in vivo results and confirm that the inhibition takes place at the hepatic level.

Chronic benzodiazepine administration. X. Concurrent administration of the peripheral-type benzodiazepine ligand PK11195 attenuates chronic effects of lorazepam

Chronic administration of benzodiazepine active at the tau-aminobutyric acidA receptor ("central" benzodiazepine sites) is associated with behavioral tolerance and receptor downregulation. Recent reports indicate possible interactions between central sites and benzodiazepines active at "peripheral-type" sites located primarily on non-neuronal cells. To evaluate these interactions during chronic administration, we treated mice with lorazepam for 1 to 14 days alone or in combination with the peripheral-type site ligand PK11195 [N-methyl-N-(methyl-1-propyl)chloro-2-phenyl-1-isoquinoline-3-carboxamid e]. Lorazepam was associated with tolerance at 7 days, but tolerance was not observed during concurrent administration of PK11195. Lorazepam was also associated with benzodiazepine receptor down-regulation in cortex and hippocampus at 7 days. With concurrent administration of PK11195, this effect remained in cortex but was absent in hippocampus. tau-Aminobutyric acid-dependent chloride uptake was reduced in both cortex and hippocampus with lorazepam, but not with concurrent lorazepam and PK11195. PK11195 administration alone did not affect behavior or neurochemical parameters, or did it alter brain lorazepam concentrations. These data indicate that concurrent PK11195 administration attenuates behavioral and neurochemical effects of chronic lorazepam administration.

Effect of halothane anesthesia and trifluoroacetic acid on protein binding of benzodiazepines

The in vitro effect of the halothane metabolite, trifluoroacetic acid, on the protein binding of three different benzodiazepines (diazepam, lorazepam and midazolam) has been investigated. Furthermore, protein binding of these drugs was studied in serum from patients under the effect of halothane anesthesia (1-2.5%; 2.5 h). Trifluoroacetic acid, 4 mmol/l, displaced diazepam and midazolam from serum and produced a marked increase in the free percentage, but did not influence lorazepam binding. Moreover, 48 h after the end of halothane anesthesia, there were changes in protein binding of diazepam (3.9 +/- 0.3% at 48 h vs. 3.3 +/- 0.3% before halothane anesthesia; p less than 0.05). It can be concluded that halothane anesthesia (1-2.5%; 2.5 h) may temporarily potentiate the pharmacological effect of diazepam in the postoperative period following anesthetic procedures.

[Interaction of the hypnotic lormetazepam with central benzodiazepine receptor subtypes omega 1, omega 2 and omega 3]

To clarify the action of lormetazepam, 3-hydroxybenzodiazepine, on the benzodiazepine (BZ) receptor subtypes, effects of lormetazepam on motor performance in the traction test and hexobarbital-induced loss of righting reflex in mice and the binding to BZ receptor subtypes were investigated in comparison with those of other BZ hypnotics. Lormetazepam prolonged the duration of hexobarbital-induced loss of righting reflex. The minimal effective dose (1 mg/kg, p.o.) was higher than that of flunitrazepam, lower than those of diazepam and zopiclone, and the same as those of triazolam and brotizolam. Lormetazepam showed the ataxic effect at 10 mg/kg, p.o., but the separation between its effective doses for the hypnotic and ataxic effects was the largest among the hypnotics tested. In the displacement study on [3H]flumazenil binding to cerebellar and spinal cord membranes, lormetazepam bound with a higher affinity to omega 1 receptor (Ki = 10 nM) than to omega 2 receptor (Ki = 29 nM). The GABA-ratios of lormetazepam to omega 1 and omega 2 receptors were 3.9 and 4.0, respectively; and they were higher and lower than those of flunitrazepam to omega 1 and omega 2 receptors, respectively. In the displacement study on [3H] Ro5-4864 binding to kidney membranes, lormetazepam bound with a lower affinity to the omega 3 receptor (Ki = 213 nM) than flunitrazepam. Thus, lormetazepam was suggested to be a potent hypnotic with weaker ataxic effects than other BZ hypnotics, which may be due to its selective and potent agonistic action on central omega 1 receptors.

Enantioselective hydrolysis of lorazepam 3-acetate by esterases in human and rat liver microsomes and rat brain S9 fraction

Rates of hydrolysis of racemic and enantiomeric lorazepam 3-acetates (LZA) by esterases in human and rat liver microsomes and rat brain S9 fraction were compared. LZA and its hydrolysis product were analyzed by chiral stationary phase HPLC. When rac-LZA was the substrate, the (R)-LZA was hydrolyzed 2.7-fold and 6.8-fold faster than the (S)-LZA by esterases in rat and human liver microsomes, respectively. In contrast, esterases in rat brain S9 fraction were enantioselective toward the (S)-LZA. The specific activities (nmol of LZA hydrolyzed/mg protein/min) of liver microsomes in the hydrolysis of enantiomerically pure (R)-LZA were approximately 210 (rat) and 1330 (human), and in the hydrolysis of enantiomerically pure (S)-LZA were 25 (rat) and 8 (human). The specific activities of rat brain S9 fraction in the hydrolysis of enantiomerically pure (R)-LZA and (S)-LZA were approximately 3 and 6 nmol/mg protein/min, respectively. Results also indicated an enantiomeric interaction in the hydrolysis of rac-LZA; the presence of (R)-LZA stimulated the hydrolysis of (S)-LZA by all esterase preparations, whereas the presence of (S)-LZA stimulated the hydrolysis of (R)-LZA in rat brain S9 fraction and inhibited the hydrolysis of (R)-LZA in rat and human liver microsomes.

Contribution of the gastrointestinal tract to lorazepam conjugation and clonazepam nitroreduction

Domestic pigs received single intravenous and oral doses of lorazepam or clonazepam (1 mg/kg), benzodiazepine derivatives biotransformed by glucuronide conjugation and nitroreduction, respectively. Blood samples were simultaneously drawn from portal venous and systemic venous sampling sites during 8 h after dosage. After intravenous dosage with either drug, the area under the serum concentration curve (AUC) for the intact drug, as well as for the principal metabolites (lorazepam glucuronide and 7-aminoclonazepam, respectively), was nearly identical between portal and systemic serum. After oral dosage, absolute systemic availability (relative to intravenous administration) of both lorazepam and clonazepam was incomplete (mean values: 29 and 49%, respectively); however, metabolite levels were also correspondingly lower between oral and intravenous dosages. First-pass hepatic extraction also occurred for both drugs, with mean systemic/portal AUC ratios of 0.60 for lorazepam and 0.74 for clonazepam. Pretreatment with neomycin (1.0 g) had a minimal effect on portal or systemic AUC for intact clonazepam after oral dosage, but 7-aminoclonazepam concentrations were reduced by neomycin pretreatment. Thus incomplete absorption, together with first-pass hepatic biotransformation, appears to explain the incomplete systemic availability of orally administered lorazepam or clonazepam. Biotransformation within the gastrointestinal tract or during absorption through the gastrointestinal mucosa contributes minimally.

Abecarnil, a metabolically stable, anxioselective beta-carboline acting at benzodiazepine receptors

Abecarnil (isopropyl 6-benzyloxy-4-methoxymethyl-beta-carboline-3-carboxylate) is a novel ligand for central benzodiazepine (BZ) receptors, possessing anxiolytic and anticonvulsant properties, but with considerably reduced muscle relaxant effects in comparison to diazepam (DZP). In vitro, abecarnil inhibited the binding of the BZ [3H]lormetazepam to rat cerebral cortex membranes with an IC50 value of 0.82 nM in comparison to 56 nM for DZP. The ability of abecarnil to displace [3H]lormetazepam was enhanced 1.24-fold in the presence of 30 microM gamma-aminobutyric acid; the corresponding value for DZP was 2.8-fold. DZP and abecarnil were equally effective in enhancing the binding of t-[35S]butylbicyclophosphorothionate to rat cortical membranes. In vivo, abecarnil exhibited a 3- to 6-fold higher affinity to forebrain BZ receptors than DZP. Abecarnil was from 2 to 10 times more potent than DZP in most rodent tests of anxiolytic activity, and in reducing locomotor activity in mice and rats thoroughly habituated to the test chamber. However, in rats newly exposed to a novel cage, abecarnil was less potent than DZP in reducing locomotor activity. In tests of motor coordination, abecarnil, in contrast to DZP, showed no or only weak activity, and in potentiating the effects of ethanol and hexobarbital on motor performance abecarnil was 4 to 25 times less potent than DZP. Abecarnil antagonized the effects of BZs in the chimney and loss of righting reflex tests, but not in the rotarod test.(ABSTRACT TRUNCATED AT 250 WORDS)

Partial GABA agonist activity of SR 95531 on the binding of [35S]TBPS, [3H]DMCM and [3H]lormetazepam to rat brain membranes

A recently developed series of pyridazinyl-GABA derivatives has been classified as GABA antagonists in electrophysiological, behavioral and biochemical experiments. These substances seemed superior to the classical GABA antagonist bicuculline because of their water-solubility, high potency and apparent selectivity for GABAA receptors. In the present study the most potent representative of this class, SR 95531 almost completely reversed the stimulatory or inhibitory effect of GABA on [3H]lormetazepam and [35S]TBPS binding, respectively. To a lesser extent, it antagonized the inhibition of [3H]DMCM binding by GABA. However, the interaction of SR 95531 with the GABA receptor seems to be of a complex nature since the compound enhanced the binding of [3H]lormetazepam by 28% at 37 degrees in the presence of 200 mM Cl-. Bicuculline inhibited [3H]lormetazepam binding under these conditions, presumably by antagonizing the effect of residual endogenous GABA. Similar to GABA and THIP, SR 95531 potently inhibited the binding of [3H]DMCM and [35S]TBPS, suggesting SR 95531 to be a partial agonist at the GABAA receptor.

Increase of natural benzodiazepines in wheat and potato during germination

Aqueous acid extracts of wheat grains and potato exhibit after HPLC separation a series of compounds that are able to inhibit the binding of benzodiazepines to benzodiazepine receptors of rat brain membranes. In wheat one of the inhibiting compounds was shown to be identical to diazepam by means of HPLC characterization and gas chromatography combined with mass spectrometry. In potato one of the most prominent components in terms of binding inhibiting activity was identified as lormetazepam. In wheat and potato germination increases total inhibiting activity of the whole plant extracts as well as the content of the benzodiazepines approximately by factor five. Because uptake of benzodiazepines from the surrounding was excluded these findings indicate the biosynthesis of the benzodiazepines diazepam and lormetazepam by the plants investigated.

Co-existence of kindling induced by the beta-carboline, FG 7142, and tolerance to diazepam following chronic treatment in mice

The effect of chronic treatment with the beta-carboline, FG 7142, followed by chronic treatment with diazepam (DZP) on the acute effects of DZP and FG 7142 were studied. Mice were treated for 16 days with FG 7142 (40 mg/kg i.p.) followed by treatment with DZP (5 or 20 mg/kg i.p.) for 9 days. At the end of this period, the anticonvulsant, antipunishment and locomotor sedative properties of a test dose of DZP were assessed, as were the convulsant properties of FG 7142. During the chronic treatment with FG 7142, 80% of the mice developed clonic convulsions in response to the beta-carboline, and this increased sensitivity to FG 7142 (kindling) remained following the chronic DZP treatment. Thus long-term treatment with DZP does not reverse the changes which occur during FG 7142-induced kindling. Chronic treatment with DZP for 9 days gave rise to tolerance to its pharmacological effects as assessed in the 4-plate test of antipunishment activity, in a test of locomotor sedation, and by its ability to increase the convulsant threshold of intravenously administered pentylenetetrazol. The development of tolerance to DZP was not affected by a prior chronic treatment with FG 7142. Nor were the acute effects induced by DZP altered by a prior chronic treatment with FG 7142. Apart from reducing its own convulsant threshold, chronic treatment with FG 7142 had no effect in any of the experiments. These results suggest that kindling induced by FG 7142 and tolerance to DZP depend on different mechanisms. In neither case were the pharmacological changes induced by chronic administration reflected by changes in the biochemical measures of the coupling between benzodiazepine binding sites and gamma-aminobutyric acid (GABA) receptors.

High density of benzodiazepine binding sites in the substantia innominata of the rat

In order to study the neuronal basis of the pharmacological interactions between benzodiazepine receptor ligands and cortical cholinergic turnover, we examined the regional distribution of specific benzodiazepine binding sites using in vitro autoradiography. In the basal forebrain, the substantia innominata contained a high density of [3H]lormetazepam (LMZ) binding sites (Bmax = 277 fmol/mg tissue; Kd = 0.55 nM). The label could be displaced by diazepam (IC50 = 100 nM), the benzodiazepine receptor antagonist beta-carboline ZK 93426 (45 nM) and the partial inverse agonist beta-carboline FG 7142 (540 nM). It is hypothesized that the amnesic effects of benzodiazepine receptor agonists are exerted through benzodiazepine receptors which are situated on cholinergic neurons in the substantia innominata and are involved in a tonic inhibition of cortical acetylcholine release. The benzodiazepine receptor antagonist ZK 93426 may exert its nootropic effects via benzodiazepine receptors in the substantia innominata and, consequently, by disinhibiting cortical acetylcholine release.

Clonazepam pharmacokinetics, brain uptake, and receptor interactions

The 7-nitrobenzodiazepine derivative clonazepam is initially biotransformed by nitroreduction, followed by acetylation. Neither the amino- nor the acetamido- metabolites appear to have important pharmacologic activity. Clonazepam elimination half-life falls in the range of 20 to 80 hours, but means within the population and variance are not well defined. Absorption of orally administered clonazepam is 80% or more. In experimental studies, clonazepam appears to diffuse passively from plasma into brain, with a constant brain-plasma concentration ratio. The drug disappears in a parallel fashion from both brain and plasma, with no evidence of sequestration in brain tissue. Clonazepam has a relatively high molar affinity for the benzodiazepine receptor in vitro, and the fractional extent of benzodiazepine receptor occupation by clonazepam in vivo is directly and predictably related to the drug's concentration in brain tissue. Acute behavioral effects are in turn directly related to the extent of receptor occupancy. Compared to other benzodiazepines, the reportedly unique clinical properties of clonazepam are neither associated with unusual/unexpected pharmacokinetic properties or with a qualitatively different in vivo interaction with the presumed benzodiazepine binding site.

Rapid increase in brain benzodiazepine receptor binding following defeat stress in mice

Defeat stress in mice, a model of social stress, increases benzodiazepine receptor binding as measured by specific [3H]Ro15-1788 binding in vivo, but not by [3H]flunitrazepam binding in vitro. This increase occurs rapidly, by 20 min following exposure to stress, and resolves by 60 min. Increased benzodiazepine receptor binding is observed in the cerebral cortex, cerebellum and hypothalamus, and appears to be due to an increase in receptor number rather than apparent affinity. The stress-induced increase in central benzodiazepine receptors is decreased in a dose-dependent fashion by lorazepam, a benzodiazepine agonist, but not by the receptor antagonist Ro15-1788. The stress-induced increase in benzodiazepine receptors is also blocked by adrenalectomy and is restored by corticosterone replacement.

Simultaneous administration of multiple model substrates to assess hepatic drug clearance

We have evaluated a method to simultaneously assess three major processes involved in hepatic drug clearance using three model substrates administered simultaneously as a 5-minute intravenous injection. Lorazepam, indocyanine green, and antipyrine are used to assess conjugation, liver blood flow, and microsomal oxidative metabolism, respectively. These substrates were administered individually and as a mixture to 10 healthy adult male volunteers to determine if clearances of any of the compounds were affected by simultaneous administration. Mean clearances of the substrates were not different when administered alone (9.97, 0.78, and 0.53 ml/min/kg) vs. together (11.5, 0.89, and 0.52 ml/min/kg), using a paired t test. Since we were using this method to assess hepatic drug clearance in children with leukemia, the effect of short-term allopurinol was assessed. The three model substrates were administered to the volunteers after 0, 1, 8, and 22 days of treatment with allopurinol, 200 mg t.i.d. There was no change in mean clearance of any of the three compounds at any point during allopurinol treatment (repeated-measures ANOVA). We conclude that this technique is a simple and valid method to simultaneously assess three major processes involved in hepatic drug clearance and is not affected by up to 22 days of oral allopurinol treatment. This simple technique, requiring a single set of blood samples, has potential applications in the assessment of developmental changes in hepatic drug clearance, as well as the effects of environmental, therapeutic, and pathophysiologic factors on three major processes involved in hepatic drug clearance.

Hepatic drug clearance in children with leukemia: changes in clearance of model substrates during remission-induction therapy

We administered a "cocktail" of three model substrates for hepatic processes: antipyrine for oxidation, lorazepam for glucuronidation, and indocyanine green for hepatic blood flow, to children with acute lymphocytic leukemia (ALL). The plasma clearance of these substrates was determined before and after remission-induction therapy in 14 children with ALL. We found an improvement in clearance of antipyrine (0.65 to 0.95 ml/min/kg; P less than 0.01) and lorazepam (0.93 to 1.20 ml/min/kg; P less than 0.05) in 12 of 14 patients, with a mean increase of 67% and 52%, respectively, from before to after remission. There was no significant difference in mean indocyanine green clearance from before to after induction (14.8 vs. 14.4 ml/min/kg). There were no significant differences in liver function test results (SGOT, prothrombin time, or serum bilirubin) from before to after induction. Plasma concentrations of albumin, alpha 1-acid glycoprotein, and apolipoprotein A changed by a mean of +11.1%, -38.2%, and +68.6%, respectively, from before to after remission. However, these changes did not account for the changes in total plasma clearance of lorazepam, because lorazepam free fraction did not change and lorazepam free clearance increased by a mean of 83%. Our hypothesis is that eradication of hepatic leukemic infiltration by ALL remission therapy resulted in an improvement in microsomal metabolism of antipyrine and lorazepam.

Benzodiazepine receptor occupancy in vivo: correlation with brain concentrations and pharmacodynamic actions

A tracer radioligand technique employing [3H]Ro 15-1788 was used to measure in vivo benzodiazepine receptor occupancy in mice. Animals were administered clonazepam (CNZ) or lorazepam (LRZ) i.p. or i.v., followed by [3H]Ro 15-1788. Plasma and cerebral cortical concentrations of the drug and cortical benzodiazepine receptor occupancy were determined at varying doses and times after administration. For both drugs, plasma and brain concentrations decreased in parallel with decreasing doses and with time, and the brain/plasma ratios remained constant. Receptor occupancy was maximal for CNZ and LRZ at doses above 1 and 4 mg/kg, respectively, and decreased with decreasing doses. Comparison of receptor occupancy with brain concentration yielded IC50 values of 21 ng/g for CNZ and 133 ng/g for LRZ. The apparent dissociation constant (Kd) for CNZ was 56 pmol/g and, for LRZ, 372 pmol/g. Hill plots yielded slopes of 1.30 for CNZ and 1.71 for LRZ. Alterations in the nonspecific uptake or elimination of Ro 15-1788 did not explain occupancy changes, inasmuch as brain concentrations of unlabeled Ro 15-1788 (6 mg/kg) were not changed by LRZ administration. The correlation between receptor occupancy and the pharmacodynamic actions of these drugs in blocking pentylenetetrazol seizures and inducing rotarod ataxia indicated that ED50 for these effects occurred at receptor occupancy of 30 to 60% for both drugs.

Pharmacokinetics of chlordesmethyldiazepam after single-dose oral administration in humans

The pharmacokinetics of chlordemethyldiazepam--a pharmacologically very active new 1,4-benzodiazepine derivative--in healthy subjects after administration of a single oral dose of 2 mg, was studied. Peak concentrations were reached in 1.2 +/- 0.2 hours. Plasma levels declined with a biphasic pattern, and the elimination phase had a half-life of 82.9 +/- 14.1 hours. The concentrations of the main metabolite of chlordemethyldiazepam, lorazepam, were about 7% of those of the parent compound. In urine only conjugated lorazepam could be found its 96 hour excretion reaching about 15% of the administered dose of parent drug.

Pharmacokinetic and dynamic studies with a new anxiolytic imidazo-pyridine alpidem utilizing pharmaco-EEG and psychometry

In a double-blind, placebo-controlled study the pharmacokinetic and pharmacodynamic effects of a new imidazo-pyridine derivative, alpidem (SL80.0342) and the 1,4 benzodiazepine lorazepam were investigated utilizing quantitative EEG and psychometric testing. Ten normal volunteers received randomized (latin square) single oral doses of placebo, 25 mg, 50 mg and 100 mg alpidem and 2.5 mg lorazepam at weekly intervals. Blood level sampling, EEG recordings, evaluation of pulse, blood pressure and side-effects were carried out at 0, 1, 2, 4, 6 and 8 hours post drug; psychometric and psychophysiological investigations at the same time periods except for the first hour. Computer-assisted spectral-analysis of the EEG demonstrated an anxiolytic profile after both compounds, characterized by an increase of beta activity, decrease of alpha activity and acceleration of the centroid of the total activity and total beta activity. Total power was attenuated, delta activity augmented and the centroid of the combined delta and theta activities decreased. The latter changes were most pronounced after 2.5 mg lorazepam suggesting it is more sedative than alpidem. Dose/treatment efficacy calculations revealed 2.5 mg lorazepam as the most CNS-active compound, followed by 100 mg, 50 mg and 25 mg alpidem. Based on a multivariate analysis 2.5 mg lorazepam could be differentiated from placebo at all times, 100 mg alpidem in the first, second and fourth hours, 50 mg only in the second hour. Time-efficacy calculations showed a marked CNS effect after alpidem in the first hour with a peak in the second hour, a gentle decline to the fourth hour and thereafter a rapid decline up to the eighth hour. In contrast, 2.5 mg lorazepam showed a slower rise in CNS activity which peaked in the fourth hour and declined slowly thereafter. These pharmacodynamic effects paralleled the blood level course of both compounds, as well as the time-course of psychometric changes. The latter were characterized by a deterioration in psychometer function after 2.5 mg lorazepam, which was less pronounced after 100 mg alpidem, while 50 mg and 25 mg showed no significant difference from placebo. Subjective ratings of mood showed a decrement which was most pronounced after 100 mg alpidem, less so after 50 mg, with no difference from placebo after 25 mg or lorazepam. Finally, there were no significant inter-drug differences with regard to psychophysiological variables.

Stereoselective binding of 3-acetoxy-, and 3-hydroxy-1,4-benzodiazepine-2-ones to human serum albumin. Selective allosteric interaction with warfarin enantiomers

Stereoselective binding of oxazepam, lorazepam, temazepam and methyl lorazepam as well as of their acetates to human serum albumin was investigated by different techniques. The 2'-chlorine and the N(1)-methyl substitution exert opposite effects on the antipodes. Enantiomers of oxazepam acetate (OAc) and lorazepam acetate (LAc) displace diazepam. Allosteric interactions with warfarin were manifested by either mutually increased or decreased binding depending on the structure of benzodiazepine and on the configuration of both benzodiazepine and warfarin. The most remarkable effect could be observed in the simultaneous binding of (S)-lorazepam acetate and (S)-warfarin.

Evidence of specific benzodiazepine binding to myometrial membrane preparations from human pregnant uterus

The muscle relaxant effect of benzodiazepines (BDZ) is widely held to be mediated at central as well as at peripheral level. In this study we report that crude membrane preparations from the myometrium of pregnant women possess binding sites for [3H]-RO 5-4864, specific ligand for the peripheral type of BDZ receptor. Scatchard analysis shows a high affinity binding site (KD = 3.1 +/- 1.2 nM) and a class of low affinity binding sites (KD greater than 30 nM). Displacement experiments show that various BDZ are differently effective in inhibiting [3H]-RO 5-4864 binding: RO 5-4864 greater than diazepam greater than flunitrazepam greater than lorazepam greater than chlordiazepoxide. In conclusion, these data seem to demonstrate that human myometrium possesses specific binding sites of 'peripheral type' for BDZ. It may be suggested that these binding sites are involved in mediating the myometrial relaxant effect exerted by BDZ. Thus, peripherally active BDZ could be used as tocolytic agents, avoiding BDZ central effects.

Lack of effect of nizatidine on hepatic drug metabolism in man

The effect of nizatidine, a new H2-receptor antagonist, on the hepatic metabolism of three probe drugs was studied in normal volunteers. The drugs studied were chlordiazepoxide and theophylline which are metabolized in part by N-demethylation by the hepatic microsomal cytochrome P-450 system and lorazepam which is conjugated to lorazepam glucuronide. A 7 day course of nizatidine did not interfere with the disposition of any of these therapeutic agents in man.

Idiosyncratic pharmacokinetics complicating treatment of major depression in an elderly woman

A 64-year-old woman with major depression developed toxic symptoms while on a regimen of 150 to 200 mg/day of desipramine. Her elimination half-life for desipramine was found to be greatly prolonged, at approximately 150 hours. Her ability to metabolize diphenhydramine and lorazepam was found to be impaired as well. Study of the elimination kinetics of desipramine in three of the patient's sisters provided some support for the existence of a genetically determined metabolic defect. Knowledge of those idiosyncratic pharmacokinetics had important implications for diagnosis and treatment in this case.

Selective interaction of novel anxiolytics with 5-hydroxytryptamine1A receptors

Radioligand binding studies were used to analyze the interactions of two novel anxiolytics, buspirone and TVX Q 7821, with a series of 10 neuronal membrane receptor sites. Buspirone (IC50 = 24 nM) and TVX Q 7821 (IC50 = 9.5 nM) display the highest affinity for 5-hydroxytryptamine1A (5-HT1A) binding sites labeled by 3H-8-hydroxy-2-(di-n-pro-pylamino) tetralin (DPAT). By contrast, buspirone is 16-fold weaker at dopamine (D2) receptors (IC50 = 380 nM), whereas TVX Q 7821 is 6-fold less potent at alpha-adrenergic1 sites (IC50 = 58 nM). At the other receptors studied, buspirone and TVX Q 7821 had similar pharmacological profiles. Both agents display moderate affinity for histamine (H1), alpha-adrenergic2, and 5-HT2 binding sites. The drugs are essentially inactive at 5-HT1B, calcium channel antagonist, muscarinic cholinergic, and benzodiazepine receptors. These results suggest that the anxiolytic effects of buspirone and TVX Q 7821 may be mediated by central 5-HT1A receptors.

Probenecid impairment of acetaminophen and lorazepam clearance: direct inhibition of ether glucuronide formation

Eleven subjects received acetaminophen (650 mg i.v.) on two occasions in random sequence, with and without concurrent administration of probenecid (500 mg) every 6 hr. Nine subjects similarly received lorazepam (2 mg. i.v.) with and without concurrent probenecid. Acetaminophen half-life was prolonged during probenecid treatment (mean +/- S.E., 4.30 +/- 0.23 vs. 2.51 +/- 0.16 hr; P less than .001) due to markedly decreased clearance (178 +/- 13 vs. 329 +/- 24 ml/min; P less than .001) with no change in volume of distribution (65 +/- 4 vs. 69 +/- 3 l; NS). Urinary excretion of acetaminophen glucuronide during 24 hr was decreased (84 +/- 9 vs. 260 +/- 21 mg of acetaminophen as glucuronide; P less than .001) and acetaminophen sulfate excretion was increased (323 +/- 25 vs. 217 +/- 17 mg of acetaminophen as sulfate; P less than .005) during concurrent probenecid treatment. However, the sum of the two conjugated metabolites was not significantly different (407 +/- 28 vs. 476 +/- 20 mg of acetaminophen as glucuronide plus sulfate excreted per 24 hr; NS). Lorazepam half-life was also prolonged during probenecid treatment (33.0 +/- 3.9 vs. 14.3 +/- 1.08 hr; P less than .001) due to decreased clearance (44.7 +/- 5.4 vs. 80.3 +/- 13.2 ml/min; P less than .001) with no change in volume of distribution (111 +/- 5 vs. 111 +/- 7 l; NS). Formation of the ether glucuronides of acetaminophen and lorazepam is impaired markedly by therapeutic doses of probenecid. Sulfate conjugation is not affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Temporal variations of lorazepam pharmacokinetics

Lorazepam pharmacokinetics were evaluated in eight healthy male and eight healthy female subjects after a single 3.5 mg oral dose. This randomized crossover study consisted of a morning dose (7:00 a.m.) or an evening dose (7:00 p.m.) separated by one week. While no consistent temporal changes in any parameter characterizing elimination of lorazepam were observed, absorption constant rate (Ka) and absorption half-life (t1/2a) were significantly modified by the hour of administration, the drug being more rapidly absorbed after the morning (t1/2a = 0.52 +/- 0.11) than after the morning trial (t1/2a = 1.18 +/- 0.26, p less than 0.05). Daily differences in pharmacokinetic parameters observed in this work suggest the need for taking in account the hour of administration during its pharmacokinetics determination.

Effects of influenza virus vaccine on hepatic drug metabolism

Experimental and more limited clinical studies have suggested that influenza vaccination may depress the oxidative hepatic metabolism of various drugs and lead to drug toxicity. The alleged mechanism is the formation of interferon and the resulting decrease in cytochrome P-450 available for drug oxidation. Because of the clinical and basic science implications of these reports, we undertook to study the effects of influenza vaccine on the metabolism of three commonly used drugs: chlordiazepoxide, theophylline, and lorazepam. Our healthy male subjects were studied just before and 1 and 7 days after vaccination. As expected, lorazepam metabolism, which proceeds by glucuronidation and not oxidation, was not altered by vaccination. Surprisingly, however, the oxidation of chlordiazepoxide was also not depressed by the vaccine. Theophylline oxidation, which proceeds primarily by microsomal oxidation (demethylation), was significantly decreased 1 day, but not 7 days, after vaccination. Serum alpha-interferon levels rose after vaccination for only about 8 hours, and levels of gamma-interferon rose to about 500 IU/ml at 24 hours, peaked at 72 hours, and returned to normal by 100 hours after dosing. It appeared that the higher the theophylline clearance before vaccination, the greater the degree of clearance depression after vaccination. Thus the inhibition of drug oxidation after influenza vaccination is selective and each drug should be studied individually. The degree of depression of theophylline clearance is small and transient and appears to be greater in subjects with higher prevaccination clearance.

Rebound insomnia and elimination half-life: assessment of individual subject response

Following abrupt withdrawal of five benzodiazepine hypnotics, the presence of rebound insomnia on individual subject nights was evaluated in comparison to a placebo group. During the first three nights of withdrawal, the frequency of occurrence of rebound insomnia for drugs with relatively rapid rates of elimination (triazolam, midazolam, and lormetazepam) was significantly higher than that for the placebo control group. In contrast, the frequency of withdrawal sleep difficulty for two slowly eliminated hypnotics (flurazepam and quazepam) was similar to that of the placebo control group during each of five successive three-night segments of a 15-night withdrawal period. These findings, based on individual subject-night data, confirm and extend previous reports using group mean values that demonstrate a frequent, immediate, and intense degree of rebound insomnia following abrupt withdrawal of relatively rapidly eliminated hypnotic drugs and an infrequent, delayed, and milder degree of sleep difficulty following withdrawal of slowly eliminated drugs.

Kinetics of diazepam, midazolam, and lorazepam in cigarette smokers

Ten otherwise healthy cigarette smokers (mean, 31 cigarettes per day), and ten nonsmoking control volunteers matched for age, weight, and sex received single intravenous doses of diazepam (5 to 10 mg), midazolam (5 mg), and lorazepam (2 mg) on three separate occasions. Kinetics of each benzodiazepine were determined from multiple serum concentrations measured after each dose. In non-smoking vs smoking subjects, there was no significant difference in mean clearance of diazepam (0.44 vs 0.47 ml/min/kg), midazolam (9.6 vs 7.1 ml/min/kg), or lorazepam (0.96 vs 1.08 ml/min/kg). Thus, differences in pharmacokinetics are unlikely to account for altered sensitivity to benzodiazepines that may occur in cigarette smokers.