Benzodiazepine pharmacodynamics: evidence for biophase rate limiting mechanisms

Individual psychomotor impairment in relation to zopiclone and ethanol concentrations in blood--a randomized controlled double-blinded trial

AIMS

To investigate individual traffic-relevant impairment related to measured blood zopiclone and ethanol concentrations. Also, we aimed to study possible development of acute tolerance.

DESIGN

A randomized controlled four-way cross-over double-blind trial. Study drugs were zopiclone 5 or 10 mg, 50 g ethanol or placebo.

SETTING

Laboratory study with computerized tests: Connor's Continuous Performance test, Choice Reaction Time and Stockings of Cambridge. Altogether, the tests consisted of 15 test components, representing three levels of behaviour (automotive, control, executive planning), relevant to traffic safety.

PARTICIPANTS

Sixteen healthy male volunteers.

MEASUREMENTS

Each study day, 10 blood samples were collected from each volunteer. Fifteen psychomotor test components were registered at baseline and a further three times after intake. Impairment was defined as any individual deterioration in performance compared to individual baseline performance.

FINDINGS

Blood drug concentrations up to 74 µg/l zopiclone and 0.100% ethanol were measured. We found a clear positive concentration-effect relationship for zopiclone and ethanol for both automotive and control behaviours, and a modest relationship for executive planning behaviour. Significant impairment started to be observed at concentrations above 16 µg/l zopiclone (automotive and control behaviour) and above 0.026% ethanol (automotive behaviour). Acute tolerance was found for both drugs.

CONCLUSIONS

The hypnotic, zopiclone, can impair psychomotor performance at blood concentrations as low as 16 µg/l.

Pharmacokinetics, pharmacodynamics and the pharmacokinetic/ pharmacodynamic relationship of zolpidem in healthy subjects

Zolpidem is one of the most frequently prescribed hypnotics, as it is a very short-acting compound with relatively few side effects. Zolpidem's short duration of action is partly related to its short elimination half-life, but the associations between plasma levels and pharmacodynamic (PD) effects are not precisely known. In this study, the concentration-effect relationships for zolpidem were modelled. Zolpidem (10 mg) was administered in a double-blind, randomised, placebo-controlled trial to determine PD and pharmacokinetics (PK) in 14 healthy volunteers. Zolpidem was absorbed and eliminated quickly, with a median T(max) of 0.78 h (range: 0.33-2.50) and t(1/2) of 2.2 h. Zolpidem reduced saccadic peak velocity (SPV), adaptive tracking performance, electroencephalogram (EEG) alpha power and visual analogue scale (VAS) alertness score and increased body sway, EEG beta power and VAS 'feeling high'. Short- and long-term memory was not affected. Central nervous system effects normalised more rapidly than the decrease of plasma concentrations. For most effects, zolpidem's short duration of action could be adequately described by both a sigmoid E(max) model and a transit tolerance model. For SPV and EEG alpha power, the tolerance model seemed less suitable. These PK/PD models have different implications for the mechanism underlying zolpidem's short duration of action. A sigmoid E(max) model (which is based on ligand binding theory) would imply a threshold value for the drug's effective concentrations. A transit tolerance model (in which a hypothetical factor builds up with time that antagonises the effects of the parent compound) is compatible with a rapid reversible desensitisation of GABAergic subunits.

Different acute tolerance development to EEG, psychomotor performance and subjective assessment effects after two intermittent oral doses of alprazolam in healthy volunteers

BACKGROUND/AIMS

Benzodiazepines (BZDs) are the most effective of the psychotropic drugs in the treatment of anxiety disorders. Tolerance has been reported for the majority of BZDs after chronic administration. However, little attention has been paid to the possibility that tolerance might be present after the intermittent oral administration of BZDs. The objectives of the present study were to assess tolerance development after the administration of two intermittent single oral doses of alprazolam given 15 days apart in healthy volunteers, and to compare the results obtained using measures from different domains: neurophysiological, psychomotor and subjective.

METHODS

Twenty-four healthy volunteers received 2 mg of alprazolam orally on two experimental days, 15 days apart. Plasma concentrations and pharmacodynamics (PD) were assessed before drug intake and at different times in the following 24 h. PD was assessed through EEG (relative alpha and relative beta-1 activities), cancellation task (total and correct number of responses) and visual analogue scales (activity and drowsiness).

RESULTS

No differences were observed in the PKs of alprazolam between occasions. A proteresis was present in both administrations for impairments of psychomotor performance and relative beta-1 activity, whereas it was present only after the second administration for subjective assessments and relative alpha activity. The proteresis on the second occasion was higher than on the first one.

CONCLUSIONS

The administration of two single oral doses of alprazolam, 2 weeks apart in healthy volunteers, yielded the same PKs on both occasions, but significant changes were observed in the PD profile. Acute tolerance was observed after the second administration. Two patterns of acute tolerance development were obtained: (1) impairments of psychomotor performance and relative beta-1 activity, and (2) subjective assessments and relative alpha activity.

Clinical pharmacology, clinical efficacy, and behavioral toxicity of alprazolam: a review of the literature

Alprazolam is a benzodiazepine derivative that is currently used in the treatment of generalized anxiety, panic attacks with or without agoraphobia, and depression. Alprazolam has a fast onset of symptom relief (within the first week); it is unlikely to produce dependency or abuse. No tolerance to its therapeutic effect has been reported. At discontinuation of alprazolam treatment, withdrawal and rebound symptoms are common. Hence, alprazolam discontinuation must be tapered. An exhaustive review of the literature showed that alprazolam is significantly superior to placebo, and is at least equally effective in the relief of symptoms as tricyclic antidepressants (TCAs), such as imipramine. However, although alprazolam and imipramine are significantly more effective than placebo in the treatment of panic attacks, Selective Serotonin Reuptake Inhibitors (SSRIs) appear to be superior to either of the two drugs. Therefore, alprazolam is recommended as a second line treatment option, when SSRIs are not effective or well tolerated. In addition to its therapeutic effects, alprazolam produces adverse effects, such as drowsiness and sedation. Since alprazolam is widely used, many clinical studies investigated its cognitive and psychomotor effects. It is evident from these studies that alprazolam may impair performance in a variety of skills in healthy volunteers as well as in patients. Since the majority of alprazolam users are outpatients, this behavioral impairment limits the safe use of alprazolam in patients routinely engaged in potentially dangerous daily activities, such as driving a car.

Lorazepam induces an atypical dissociation of visual and auditory event-related potentials

Lorazepam has been reported to atypically disrupt visual processing compared to other benzodiazepines (BZs), but it is not known to what extent this effect extends to impairment in other modalities. Our objective was to compare the effects of lorazepam with those of flunitrazepam, a BZ with standard effects, on visual and auditory event-related potentials (ERPs) using the same paradigm. The study followed a placebo-controlled, double-blind, parallel group-design and involved single oral doses of lorazepam (2.0 mg), flunitrazepam (1.2 mg) and placebo. Thirty-six young, healthy subjects completed a test battery before and after treatment including classic behavioural tests, visual and auditory ERPs. Both drugs led to comparable alterations on behavioural tests and double-dissociations were found, indicating that the doses used were equipotent: lorazepam was more deleterious than flunitrazepam and placebo in fragmented shape identification, while simple reaction times were prolonged for flunitrazepam in comparison to lorazepam and placebo. Effects on P3 latencies were also distinct: alterations in both modalities for flunitrazepam were equivalent and greater than placebo's. In contrast, lorazepam at the frontal and central electrode sites led to greater changes in visual than in auditory latency, and also to longer visual latencies than flunitrazepam and placebo, but lorazepam's auditory latency effects were only different to placebo's at the parietal electrode site. Peripheral visual changes were not responsible for these effects. Differences in the impairment profile between equipotent doses of lorazepam and flunitrazepam suggests that lorazepam induces atypical central visual processing changes.

Clinical impairment of benzodiazepines--relation between benzodiazepine concentrations and impairment in apprehended drivers

BACKGROUND

Acute intake of benzodiazepines is followed by concentration-dependent deterioration of performance in controlled experimental studies. Whether this is true in a population of benzodiazepine users is uncertain. We studied the relationship in a population of suspected drugged drivers.

METHODS

In Norway physicians examine and take blood samples from nearly all suspected drivers. Our material comprised 818 samples containing only one benzodiazepine and our reference group consisted of 10,759 cases containing only alcohol.

RESULTS

159 drivers (19%) were considered as not impaired and 659 (81%) as impaired. None of the background factors, e.g. gender, age or time of day when apprehended, related significantly to either the physician's conclusion or to blood levels of benzodiazepines. Impaired subjects had significantly higher blood levels of diazepam (n=411) (P<0.001), oxazepam (n=73) (P<0.05) and flunitrazepam (n=211) (P<0.05) than those not impaired. The risk of being assessed as impaired did rise with increasing benzodiazepine blood level, with odds ratios (ORs) for being assessed as impaired of 1.61, 3.65 and 4.11 for the three supratherapeutic drug levels. The corresponding OR found for different elevated blood-alcohol concentrations were 1.49, 2.94 and 10.49.

CONCLUSION

The blood concentration of benzodiazepines was the only characteristic which was related to impairment. This indicated a drug-concentration related effect of benzodiazepines on performance and paves the way for a discussion on legal limits for benzodiazepines in relation to driving.

A double-dissociation of behavioural and event-related potential effects of two benzodiazepines with similar potencies

This study was designed to explore the role of benzodiazepine affinity to benzodiazepine binding site on acute psychomotor, subjective and memory effects, as well as auditory Event Related Potential (ERP) latencies, in healthy volunteers. Two benzodiazepines with similar affinity to benzodiazepine binding sites, or potency, were compared: the atypical compound lorazepam (2.0 mg), which has been reported to impair priming, and a standard benzodiazepine, flunitrazepam (0.6 mg, 0.8 mg, 1.0 mg). The study followed a placebo-controlled, double-blind, parallel-group design. Sixty subjects completed a test battery before treatment and at theoretical peak plasma concentration of drugs. Lorazepam and 1.0 mg of flunitrazepam led to comparable alterations on psychomotor, subjective and auditory episodic memory measures. A double-dissociation was found for lorazepam and the equipotent dose of flunitrazepam (1.0 mg): lorazepam was more deleterious than flunitrazepam in time taken to identify fragmented shapes. Lorazepam also impaired direct and indirect stem-completion in comparison to placebo, but this effect was abolished when time to identify shapes was used as a covariate. By contrast, 1.0 mg of flunitrazepam prolonged auditory ERP latencies to a greater extent than lorazepam. High affinity to the benzodiazepine binding sites does not seem to explain the consistent lorazepam-induced impairment of indirect stem-completion. Differences in impairment profile between the benzodiazepines employed may relate to the modality (visual or not) of the tasks used.

A double-blind comparison of lorazepam and oxazepam in psychomotor retardation and mutism

BACKGROUND

An increasing number of case reports indicate a superior therapeutic response of catatonialike symptoms, such as severe psychomotor disturbance and mutism, associated with psychiatric disorder to the benzodiazepine lorazepam (LO). Equivocal results, however, are also reported with regard to other benzodiazepines for the treatment of this syndrome. The purpose of this study was to compare the effects of LO and oxazepam (OX), benzodiazepines with comparable pharmacokinetics, on psychomotor retardation and mutism associated with psychiatric disorder.

METHODS

Twenty-one hospitalized patients with severe psychomotor retardation and mutism were treated with 2 mg LO and 60 mg OX in a double-blind crossover study design.

RESULTS

Both benzodiazepines significantly reduced psychomotor symptoms. When administered for the first time, 4 of 7 patients with LO and 6 of 10 patients with OX improved at least 50% on visual analog scale (VAS) rating. Reduction in symptoms was significant with LO and OX treatment on either day of treatment. The second time, however, LO was significantly better compared with OX in alleviating the target symptoms.

CONCLUSIONS

Both OX and LO are effective for the treatment of psychomotor retardation. Thus, the beneficial effect of LO on psychomotor retardation and mutism is not a unique pharmacodynamic property but more likely due to its pharmacokinetic profile. The differential effect of the two benzodiazepines on the second day of treatment warrants further clarification. Several hypotheses are evaluated.

Pharmacokinetic-pharmacodynamic modelling of zopiclone effects on human central nervous system

The present data shows the pharmacokinetics and concentration-effect relationship of a single 7.5 mg oral dose of zopiclone in ten healthy volunteers. Plasma concentrations and effects of zopiclone on central nervous system as quantified by changes in saccadic peak velocity and digit symbol substitution test were measured for 17 hr after ingestion of zopiclone. Pharmacokinetics was described with a linear one-compartment open model. Maximum effects preceded peak plasma zopiclone concentrations causing a clockwise hysteresis, i.e. proteresis, in concentration versus effect loops. Therefore, pharmacodynamics was described both with a tolerance model and a model with distributional pseudo-tolerance where the concentration in the blood sampling site is assumed to equilibrate slower with arterial blood than the site of action of zopiclone. Both models related the changes in pharmacodynamics linearly to changes in zopiclone concentrations. The median (range) values for clearance, volume of distribution and elimination half-life were 21 (15-53) L/hr, 132 (58-161) L and 3.4 (1.7-5.7) hr, respectively. Both pharmacodynamic models were able to describe the relationship between zopiclone concentrations and changes in psychomotor performance equally well. However, because the pharmacodynamics of zopiclone were studied in a non-steady-state situation, the mechanism for proteresis, i.e. true tolerance versus distributional pseudotolerance cannot be identified.

Development of acute tolerance after oral doses of diazepam and flunitrazepam

Flunitrazepam (1 and 2 mg), diazepam (10 and 20 mg) or placebo was administered to healthy, male volunteers, and the time course of psychomotor impairment, as indicated by simple and complex choice reaction time and movement time, was studied during a period of 6 h after drug intake. To examine whether acute tolerance developed, the observed performance during decreasing drug plasma concentration was compared to the predicted performance based on kinetic-dynamic modelling of the observed performance during the first 1.5 h after intake when the drug plasma concentrations were increasing or at peak level. Placebo corrections of the test scores were accomplished to adjust for diurnal variation and the possible influence of learning during the test day. After the flunitrazepam treatments, the predictions overestimated the actual performance significantly with respect to simple and choice reaction time at the 6-h session after intake. After the diazepam treatments, however, no significant deviation was detected between predicted and observed performance. The results indicate that acute tolerance develops with respect to impairment of attention demanding performance after medium to large doses of flunitrazepam, and that tolerance is expressed after approximately 4-6 h following intake.

Construct validity of a new computer-assisted cognitive neuromotor assessment battery in normal and inpatient psychiatric samples

The construct validity of a computer-assisted battery of neuropsychological tests (CNT) was explored with psychiatric inpatients and normal volunteers. A principal components analysis of inpatient scores revealed simple reaction time, response accuracy, visuomotor skill, and complex processing and memory components. A similar factorial structure was found in normal subjects. However, complex processing and memory measures emerged as separate vigilance and memory components in volunteers. CNT tasks were correlated with nine subtests of the Neurobehavioral Cognitive Status Examination (NCSE). Simple reaction time, and complex processing and memory measures discriminated impaired from nonimpaired inpatients as defined by the NCSE. Recommendations for research on CNT, and computer-assisted tests in general, are made.

Abuse liability of alprazolam relative to other commonly used benzodiazepines: a review

Nonhuman and human studies comparing the abuse liability of alprazolam to other commonly used benzodiazepines are reviewed. These studies are reviewed to determine to what extent prospective, controlled, experimental studies support opinions that alprazolam's abuse liability is greater than that of other commonly used benzodiazepines. Studies comparing the self-administration of alprazolam, the discriminative stimulus effects of alprazolam, self-reported effects of alprazolam, physiological dependence on alprazolam, and adverse effects of alprazolam relative to other benzodiazepines are reviewed. Overall, the experimental literature does not support the widely held belief that alprazolam's abuse liability is greater than that of other benzodiazepines, but much more research is needed. Such research should focus explicitly on alprazolam's reinforcing effects, and the nature and severity of the discontinuation syndrome associated with its long-term use. Important issues such as selection of an appropriate comparison drug, selection of an appropriate population, dosing regimen and test doses need to be considered in future studies.

Pharmacodynamics of the anticonvulsant effect of oxazepam in aging BN/BiRij rats

1. The purpose of this investigation was to examine the influence of increasing age on the pharmacokinetics and the time course of the anticonvulsant response of oxazepam in BN/BiRij rats as an animal model of aging. 2. Oxazepam was administered intravenously in a dose of 12 mg kg-1 body weight and the anticonvulsant effect intensity was measured as elevation above baseline of a threshold for induction of localized seizure activity (TLS). Direct cortical stimulation with ramp shaped electrical pulse trains of increasing intensity was used to determine this threshold. 3. The pharmacological effect vs. time profile showed in young rats an anticonvulsant component followed by proconvulsant component which is suggestive for the occurrence of acute tolerance and/or withdrawal syndrome. With increasing age the proconvulsant component disappeared, resulting in a monophasic effect profile (anticonvulsant effect only) at the age of 35 months with significantly higher anticonvulsant effect intensity immediately following drug administration. No age-related changes in the pharmacokinetic parameters of oxazepam were observed. 4. In five animals of each age group, benzodiazepine receptor binding characteristics were determined in vitro with [3H]-flunitrazepam as a ligand. Both receptor density and affinity did not show age-related changes. Available literature data on post-receptor events do not indicate conclusive age-related changes. 5. It is concluded, that the observed change in the pharmacodynamics of anticonvulsant effect of oxazepam can be explained by the disappearance of the tolerance/withdrawal phenomenon. This is compatible with a decreased efficiency of homeostatic control mechanisms in the elderly.

The effects of alprazolam alone and combined with alcohol on central integrative activity

The effects of alprazolam 1 mg both alone and in combination with 0.5 g/kg of alcohol were examined on self-ratings of intoxication and measures of central and peripheral activity such as EEG, auditory evoked response, tremor at 90, 150 and 210 min post drug. Forty-eight healthy volunteers were assigned randomly to 4 independent groups who received: alprazolam and placebo drink, alprazolam and alcohol, placebo capsule and alcohol, placebo capsule and placebo drink respectively. Alprazolam decreased the amplitudes of the 3 potentials of the evoked response, decreased activity in the 8-13 Hz and increased activity in the 13.5-26 Hz wavebands of the EEG and decreased the frequency at which fusion was perceived. Alcohol prolonged reaction time and increased tremor. The effects were not always additive and alprazolam was dominant in the combination.

Relationship between drug plasma concentrations and psychomotor performance after single doses of ethanol and benzodiazepines

In a placebo controlled, crossover study psychomotor effects of single doses of diazepam, 10 and 20 mg, flunitrazepam, 1 and 2 mg, as well as 0.9 g ethanol/kg body weight were investigated over a time period of 6 h in 12 healthy men. Blood samples were collected simultaneously with the test sessions to determine drug concentrations in plasma or blood. The ethanol dose caused the least performance impairment, followed by 10 mg diazepam. The most pronounced impairment was caused by 2 mg flunitrazepam, whereas 20 mg diazepam and 1 mg flunitrazepam caused intermediate impairment and were approximately equipotent on group level. Considerable interindividual differences with respect to maximal impairment following a particular drug treatment were observed, with poor correlation between individual maximal impairments and individual peak plasma concentrations of the drug. The maximal impairment in simple reaction time following the flunitrazepam treatments occurred earlier relative to the peak plasma concentration of the drug as compared to the diazepam treatments. This may indicate that acute tolerance develops differently for the two drugs.

A guide to benzodiazepine selection. Part I: Pharmacological aspects

Since absorption rates, volumes of distribution and elimination rates differ greatly among the benzodiazepine derivatives, each benzodiazepine has a unique plasma concentration curve. Although the time to peak plasma levels provides a rough guide, it is not equivalent to the time to clinical onset of effect. Two half-lives can be described: the alpha half-life, the rate of decline in plasma concentrations due to the process of drug redistribution from the central to the peripheral compartment, and the beta half-life, the rate of decline due to the process of drug elimination due to metabolism. The frequent classification of benzodiazepines into long, intermediate, and short-"acting" categories based on their terminal beta half-lives is unfounded; the duration of action is much more dependent on the alpha half-life. Benzodiazepines with short beta half-lives are commonly thought to be preferable because they accumulate less. However, with repeated use, sedation and cognitive neuromotor impairment usually diminish progressively despite stable or even rising benzodiazepine plasma concentrations, whereas anxiolytic effects generally persist over time.

Effects of single doses of alprazolam and diazepam, alone and in combination with ethanol, on psychomotor and cognitive performance and on autonomic nervous system reactivity in healthy volunteers

Effects of alprazolam, alone and in combination with ethanol, on psychomotor and cognitive performance were studied in healthy male volunteers and compared to effects of diazepam. Alprazolam 2 mg produced relatively long-lasting impairments on tests of tracking, verbal and nonverbal information processing, and memory, and decreased blood pressure without a change in heart rate or plasma norepinephrine levels. Although ethanol consumption was demonstrated to produce additive decrements in performance on certain tasks, there was little evidence to support a synergistic effect. Alprazolam 2 mg was accompanied by increased self-reports of side effects, especially drowsiness. Low dose alprazolam, diazepam, and ethanol produced significantly fewer side effects than 2 mg alprazolam, but significantly more than placebo.

Benzodiazepine concentrations in brain directly reflect receptor occupancy: studies of diazepam, lorazepam, and oxazepam

Groups of male CF-1 mice received 3 and 10 mumol/kg diazepam, lorazepam, and oxazepam intravenously. Between 1 min and 24 h after injection, benzodiazepine concentrations were determined by gas chromatography (GLC) in plasma and in one brain hemisphere; in the other hemisphere, ex vivo benzodiazepine receptor occupancy was measured using 3H-flunitrazepam displacement. Based on GLC data, diazepam entered brain rapidly, and was also cleared rapidly, yielding desmethyldiazepam and oxazepam as metabolites in plasma and brain. However, lorazepam and oxazepam entered brain slowly, with brain:plasma equilibrium achieved at 30-60 min; thereafter, the drugs were eliminated from plasma and brain in parallel. The time course and extent of ex vivo occupancy were highly consistent with GLC data (for diazepam, GLC levels were expressed as the sum of diazepam, desmethyldiazepam, and oxazepam, with metabolite concentrations, normalized for molecular weight and for in vitro benzodiazepine receptor affinity.) Between-method correlations were 0.95 or higher. Thus benzodiazepine receptor occupancy is highly dependent on benzodiazepine concentrations in brain. Differences in the time-course of onset and duration of pharmacologic activity between the highly lipophilic benzodiazepine diazepam and the less lipophilic hydroxylated derivatives lorazepam and oxazepam are largely explained by differences in systemic kinetics and in the rate of uptake into brain.

Pharmacokinetics and pharmacodynamics of alprazolam following single and multiple oral doses of a sustained-release formulation

The pharmacokinetics and pharmacodynamics of alprazolam after IV and oral sustained-release (SR) tablet administration were evaluated in 42 healthy, normal, male volunteers. All 42 subjects received a single 1-mg intravenous (IV) alprazolam dose. After a 1-week washout period, the subjects received one of three SR treatments as a single dose: one 1-mg SR tablet, three 1-mg SR tablets, or six 1-mg SR tablets. Beginning 2 days after single-dose SR treatment, each subject received the above SR doses for 3 days. The daily dose for the multiple-dose study was the same as the subject received in the single-dose study. Serial blood samples were collected after each treatment (single-dose IV, single-dose SR, and after the last SR multiple dose), and plasma samples were analyzed by high performance liquid chromatography. Sedation was assessed by a blinded observer at each blood sampling time. Mean pharmacokinetic parameters for IV administration were consistent with previous results. Pharmacokinetic parameters for the SR doses were consistent with linear kinetics over the dosage range studied. The mean absolute bioavailabilities of the SR tablets were greater than 0.84 after single SR doses. Maximal sedation was related to dose after single-dose SR administration. During multiple dosing, chronic tolerance was observed. Maximal sedation scores after 3 days of alprazolam SR administration were independent of the dose administered and were lower after multiple-dose administration than scores observed after single oral SR doses, although plasma alprazolam concentrations were at least 1.5 times higher with multiple dosing. Sedation data indicate that oral SR doses were well tolerated in multiple dosing.(ABSTRACT TRUNCATED AT 250 WORDS)