Kinetics and neuropsychologic effects of IV diazepam in the presence and absence of its active N-desmethyl metabolite in humans

Conversion factors for assessment of driving impairment after exposure to multiple benzodiazepines/z-hypnotics or opioids

AIMS

Norway has introduced legal concentration limits in blood for 28 non-alcohol drugs in driving under the influence cases. As of 2016 this legislation also regulates the assessment of combined effects of multiple benzodiazepines and opioids. We herein describe the employed methodology for the equivalence tables for concentrations of benzodiazepines/z-hypnotics and opioids implemented in the Norwegian Road Traffic Act.

METHODS

Legislative limits corresponding to impairment at blood alcohol concentrations (BAC) of 0.02%, 0.05% and 0.12% were established for 15 different benzodiazepines and opioids. This was based on a concept of a linear relationship between blood drug concentration and impairment in drug naïve users. Concentration ratios between these drugs were used to establish conversion factors and calculate net impairment using diazepam and morphine equivalents.

RESULTS

Conversion factors were established for 14 benzodiazepines/z-hypnotics (alprazolam, bromazepam, clobazam, clonazepam, etizolam, flunitrazepam, lorazepam, nitrazepam, nordiazepam, oxazepam, phenazepam, temazepam, zolpidem and zopiclone) and two opioids (methadone and oxycodone).

CONCLUSIONS

Conversion factors to calculate diazepam and morphine equivalents for benzodiazepines/z-hypnotics and selected opioids, respectively, have been operative in the Norwegian Road Traffic Act as of February 2016. Calculated equivalents can be applied by the courts to meter out sanctions.

Postoperative cognitive dysfunction: incidence and prevention

Postoperative cognitive dysfunction (POCD) is a decline in cognitive function for weeks or months after surgery. Due to its subtle nature, neuropsychological testing is necessary for its detection. The interpretation of literature on POCD is difficult because of numerous methodological limitations, particularly the different definitions of POCD and the lack of data from control groups. POCD is common after cardiac surgery, and recent studies have now verified that POCD also exists after major non-cardiac surgery, although at a lower incidence. The risk of POCD increases with age, and the type of surgery is also important because there is a very low incidence associated with minor surgery. Regional anaesthesia does not seem to reduce the incidence of POCD, and cognitive function does not seem to improve after carotid surgery as has previously been suggested.

A double-blind study of the sedative effects of the thalidomide enantiomers in humans

This study investigated the sedative effects of the enantiomers of thalidomide in humans. Since the enantiomers undergo chiral inversion in vivo this entailed application of suitable statistical methodology to distinguish the effects of each enantiomer in the presence of the other one. Six healthy male volunteers received single oral doses of (+)-(R)-thalidomide, (-)-(S)-thalidomide or racemic thalidomide in a double-blind study, and the results of this study were compared with those of a similar study where three subjects received (+)-(R)-thalidomide, (-)-(S)-thalidomide or placebo in a double-blind fashion. Blood samples for analysis of (+)-(R)-thalidomide and (-)-(S)-thalidomide were obtained. Prior to sampling it was noted whether the subject was awake or asleep, and his feelings of tiredness and heaviness were estimated using Borg scales. After blood sampling continuous reaction time was measured by a 10-min series of auditory signals. The concentration-effect relationships were analyzed by logistic regression techniques and Cox regression for the reaction time data. The (+)-(R)-thalidomide concentrations, but not the (-)-(S)-thalidomide concentrations, exhibited significant positive influences on all sedative effects studied (sleep, tiredness, and reaction times). In some of the analyses of reaction times the (-)-(S)-thalidomide concentrations had a significant effect in the opposite direction. The time course and intensity of sedative effect is thus influenced by which enantiomer is administered and by the kinetics of in vivo chiral inversion.

Chronic administration of and dependence on halazepam, diazepam, and nordiazepam in the dog

Halazepam administered chronically to dogs in oral doses of 180 and 450 mg/kg/day produced physical dependence which was revealed by a flumazenil precipitated abstinence syndrome and measured by the Nordiazepam Precipitated Abstinence Scale score (NPAS) (McNicholas et al., 1988; Sloan et al., 1990). This abstinence as measured by the NPAS score was more severe in diazepam- and halazepam-dependent than in nordiazepam-dependent dogs whereas the incidence of precipitated clonic seizures was greater in the diazepam- and nordiazepam-dependent than in the halazepam-dependent dogs. Pharmacokinetic studies showed that in the dog the major conversion of halazepam, like diazepam, was to nordiazepam and an oxazepam conjugate. Appreciable quantities of oxazepam, 3-OH halazepam and its conjugated metabolite were also identified in plasma. The NPAS score obtained in the halazepam-dependent dogs, however, was greater than the NPAS score obtained in nordiazepam-dependent dogs who had nordiazepam plasma levels over three times higher than those obtained in the halazepam-dependent dogs. Further, the precipitated abstinence observed in the halazepam-, diazepam- and nordiazepam-dependent dogs differed in qualitative as well as in quantitative aspects including marked differences in the time course of abstinence signs. These data argue that the different dependencies produced by halazepam, diazepam and nordiazepam are not due solely to either the parent compound or to a single metabolite but most likely to their combined effects.

A comparison of the physical dependence inducing properties of flunitrazepam and diazepam

Dogs dosed chronically (4-7 weeks) with oral flunitrazepam (7.6 mg/kg/day) or diazepam (24-36 mg/kg/day) administered in 4 equally divided doses had dose-related flumazenil precipitated benzodiazepine abstinence scale scores (BPAS) of comparable intensities despite the fact that plasma levels of flunitrazepam and its metabolites were much lower than nordiazepam levels in the diazepam-dependent dog. Both groups of dependent dogs had clonic and tonic-clonic seizures after oral and IV flumazenil. Precipitated abstinence signs persisted longer in the diazepam than in the flunitrazepam-dependent dogs. Differences in the pharmacokinetics of the drugs of dependence, their metabolites, and their interactions at receptor sites offer a partial explanation for the high level of dependence seen in the flunitrazepam dog. The finding that the estimated plasma free concentration of flunitrazepam and its metabolites is equal to or greater than that of diazepam and its metabolites together with the fact that flunitrazepam has a higher affinity for the benzodiazepine receptor than either diazepam, nordiazepam or oxazepam can explain why the intensity of the precipitated abstinence syndrome is comparable in flunitrazepam- and diazepam-dependent dogs. Although the flumazenil-induced precipitated abstinence syndromes observed in flunitrazepam- and diazepam-dependent dogs differed qualitatively they did not differ quantitatively. It is therefore concluded from these data that the doses of flunitrazepam and diazepam, chosen for producing comparable degrees of weight loss during dose escalation, did not differ in the degree of physical dependence that they produced in the dog.

Determination of pharmacodynamics of diazepam by quantitative pharmaco-EEG

The relationship between the quantitative EEG variables and plasma levels after the administration of diazepam (DZ) or N-desmethyldiazepam (synthesized NDDZ) was evaluated by simultaneously measuring the power spectra for EEG with two biological markers and plasma concentrations. After a single DZ administration, the EEG change corresponding to sedation appeared rapidly and showed a short duration. A close relationship was found between these effects and changes in the DZ plasma concentrations. DZ and synthesized NDDZ had the same pharmacodynamic characteristics, but the main metabolic product of DZ (metabolite NDDZ) showed a different pharmacokinetic profile. A multiple administration of DZ or synthesized NDDZ caused some reduction in sedation at the steady-state. These results led to the conclusions that a single administration of DZ causes sedation of a short duration, and the main metabolic product of DZ (metabolite NDDZ) does not seem to contribute to sedation. In addition, the reduction in the pharmacological effect after continuous treatment with DZ depends not on autoinduction or interference, but on acute tolerance or adaptation.

Tolerance to the anticonvulsant effect of clorazepate and clonazepam in mice

The rate of development of tolerance to the benzodiazepines clorazepate and clonazepam against pentetrazole-induced seizures in mice was compared. Treatment with clorazepate (0.1% solution as drinking water) for 21 days led to tolerance beginning at day 7. When mice were treated with clonazepam (0.5 mg/kg twice daily intraperitoneally), tolerance was evident already at the fourth day of treatment. Twenty-four hours after cessation of treatment the seizure threshold was significantly decreased after treatment with both drugs. Clorazepate, a prodrug of the main metabolite of diazepam, desmethyldiazepam, regards further interest for anticonvulsant therapy because of a relatively slow onset of tolerance.

The natural history of tolerance to the benzodiazepines

Dependence on benzodiazepines following continued use is by now a well-documented clinical phenomenon. Benzodiazepines differ in their dependence potential. The present studies were aimed at examining the possibility that differential rates of tolerance development might account for differences in dependence risk. Four studies are reported. The first three studies concerned normal subjects. The development of tolerance over a fifteen day period was demonstrated for three different benzodiazepines (ketazolam, lorazepam and triazolam) using two paradigms. Tolerance in terms of a reduction in effectiveness of a repeated given dose was most notable for the benzodiazepine with a medium elimination half-life (lorazepam) for physiological, behavioural and subjective measures. In the case of the drug with the longest elimination half-life (ketazolam) reduction in effectiveness could only be assumed to be occurring if account was taken of the steady increase in plasma concentrations of active metabolites. For this drug it seemed that the physiological measures were those most likely to demonstrate the development of tolerance. Although triazolam showed few significant drug effects on this paradigm (testing being 12 hours after ingestion of this short half-life benzodiazepine), tolerance was seen to develop on some subjective measures. Using an alternative method of testing tolerance, assessing responses to a diazepam challenge dose, a high degree of tolerance on two-thirds of the measures was observed in subjects when pretreated with the benzodiazepine with the most marked accumulation of active metabolites (ketazolam). The other two drugs also led to tolerance development on a range of measures; this was more marked for lorazepam than triazolam. Blunting of the growth hormone response to diazepam was the most sensitive and reliable method of detecting tolerance to the benzodiazepines. Symptoms on discontinuation of the two weeks' intake of the benzodiazepines were marked for all the drugs but unrelated to either the tolerance induced or the elimination half-life of the particular drug. A further clinical study revealed that tolerance persisted in a group of long-term benzodiazepine users for between four months and two years following complete abstinence from the drug. These patients appeared to be less affected by diazepam in terms of its commonly observed subjective effects, regardless of their original medication. These ex-long-term users of benzodiazepines were, however, more likely to manifest two specific types of effects--immediate 'symptom' reduction and exacerbation of 'withdrawal symptoms' over the subsequent week.(ABSTRACT TRUNCATED AT 400 WORDS)

N-desmethylclobazam: a possible alternative to clobazam in the treatment of refractory epilepsy?

The development of anticonvulsant tolerance during 10 days treatment with either clobazam or its principal metabolite, N-desmethylclobazam (NDMC), was compared in mice using an i.v. infusion of pentylenetetrazole as the convulsive stimulus. Subsequently the anticonvulsant activity of NDMC was assessed in patients with refractory epilepsy. In mice, a highly significant tolerance (P less than 0.001) developed to clobazam (10 mg kg-1 twice daily). During the same period, there was no significant change (P greater than 0.05) in the protection afforded by NDMC (40 or 80 mg kg-1 twice daily) although some reduction in anticonvulsant activity was apparent. NDMC (30 mg once daily) was given to nine patients with frequent complex partial and/or grand mal seizures who had become tolerant to the anticonvulsant effect of clobazam. Seven of the patients had been free from benzodiazepine therapy for at least 2 weeks, while the other two patients were switched directly from clobazam. Eight of the nine patients showed a favourable response to NDMC. In the seven who had been given a holiday from clobazam the response to NDMC was similar to the initial response to clobazam and was achieved at plasma NDMC concentrations in the same range as those seen during clobazam administration (1000-3000 ng ml-1). It is concluded that NDMC is active as an anticonvulsant in man and there is evidence from the animal studies to suggest that it may be preferable to clobazam.

Continuous reaction times in cerebral dysfunction

The Continuous Reaction Times (CRT) method was used to examine pharmacological, psychiatric, medical and neurological problems in clinical practice where a detailed neuropsychological examination with a test battery was not possible. Either 100 visual or 150 auditory stimuli were given within a period of 6 1/2 or 10 min respectively, and the patients were instructed to react as quickly as possible to every stimulus. The same CRT method was applied to heterogeneous groups of patients with cerebral dysfunction and control subjects. The results demonstrated that it was useful as a screening test for the presence of cerebral dysfunction and was especially sensitive to progressive diseases. Its discriminative power was equivalent to more sophisticated and complex psychological tests. Even if CRT is a valid and reliable method of testing cerebral affection, the neural background for the reaction time process is still unknown and the test did not distinguish between patients with right- or left-hemisphere lesions and was not influenced by the etiology of the disease. CRT is therefore considered a provisional method, suggestive only for the actual diagnostic procedures. Only when the patients have a well-defined diagnosis e.g. a diffuse cerebral affection caused by a drug or a metabolic disorder can CRT be recommended as a measure of the degree of lowered consciousness.

Development of tolerance to the anticonvulsant effect of diazepam in dogs

In dogs the development of tolerance to the anticonvulsant effect of diazepam was followed by weekly determinations of the convulsive threshold for pentetrazole, 10-15 min after intravenous (i.v.) injection of 0.25 or 0.5 mg/kg diazepam. As soon as after 1 week of oral treatment with diazepam, 0.25 or 0.5 mg/kg three times daily (t.i.d.), the pentetrazole threshold showed a decline or even a fall to the control level in spite of unaltered or rising concentrations of diazepam and its active metabolites. Tolerance also developed when the dogs were treated with chlorazepate, 2 mg/kg t.i.d., between the weekly diazepam injections for threshold determination. The results favor a functional type of tolerance since there was no indication of a more rapid inactivation of diazepam. Treatment with desmethyldiazepam (2 mg/kg i.v. for threshold determination and oral treatment with the desmethyldiazepam precursor chlorazepate, 2 mg/kg t.i.d.) did not produce tolerance. In further experiments in dogs anesthetized, relaxed with suxamethonium and ventilated, a spike-wave activity in the EEG was induced and maintained by an injection and subsequent infusion of pentetrazole. Out of 6 dogs, receiving 4-5 i.v. injections of 0.25-0.5 mg/kg diazepam, 2 showed the phenomenon of acute tolerance, i.e. the effect of the drug on the spiking activity in the EEG became less from one injection to the next, and thus paralleled a situation which may be observed during treatment of clinical status epilepticus. No acute tolerance was observed in corresponding experiments with desmethyldiazepam.

Reaction time course during weaning from respirator treatment

Ten patients who developed disturbed mental function during respirator weaning were studied. They were investigated during respirator treatment and 1 h after start of spontaneous ventilation with continuous reaction time measurements and clinical ratings. During the spontaneous ventilation the reaction times increased and the patients experienced fatigue. PaCO2 was higher and PaO2 was lower than during respirator treatment. A significant correlation was found between individual differences of reaction times and arterial blood gas levels in the two conditions, whereas no general correlation between reaction times and arterial blood gas levels could be established. The findings must be considered tentative, but the results of this study indicate the value of continuous reaction time measurements for quantitative assessment of mental status during respirator treatment.

Pharmacokinetic and clinical studies with a benzodiazepine radioreceptor assay

Since the presence of benzodiazepine (BD) receptors was demonstrated in mammalian brain tissue, simple, sensitive and rapid techniques have been established to use BD-receptor preparations for specific radioreceptor assays (RRA). The RRA allows in vitro estimations of receptor affinity and concentration of BD in biological material, e.g. the time course of total BD binding activity in plasma (parent compound and active metabolites) may be evaluated. Several studies in volunteers with short and long-acting BD used as sedatives and hypnotics including diazepam (DZP), flunitrazepam (FNZ), flurazepam (FZP), lormetazepam (LMZ), oxazepam, temazepam and triazolam indicate that pharmacokinetic data (e.g. elimination half-lives of receptor active compounds) concur with the results obtained from other methods, if active metabolites are taken into account. For the evaluation of BD long-term and hangover effects in two placebo controlled double-blind studies (placebo vs. 1 mg and 2 mg LMZ, 2 mg FNZ, 30 mg FZP, 10 mg DZP) BD-binding equivalents and pharmaco-EEG recordings, subjective state, psychomotor as well as cognitive function were determined by standardized methods up to 154 hours following drug administration. Compared to placebo a distinct long-lasting increase in the relative power in beta-frequencies (12.5-30 Hz) and an impairment of psychomotor performance could be evidenced up to 12 h following FNZ and FZP intake. These effects correspond to the BD-binding activity in plasma. These findings indicate that BD-receptor preparations as used for the RRA are valuable tools to investigate binding affinities and pharmacokinetic properties of BD. Plasma levels of RRA active material may reflect a better correspondence to some clinical effects of BD than levels of the parent compound alone.

Are electroencephalographic and psychomotor measures sensitive in detecting residual sequelae of benzodiazepine hypnotics?

PURPOSE

The recent development of short-acting benzodiazepines without active metabolites calls for a differentiation between the hangover effects of long-acting (LBD) and short-acting (SBD) benzodiazepines, when used as nighttime sedatives. The question now arises as to which electrophysiological and psychometric tests can record these effects with the highest degree of sensitivity.

SUBJECTS AND METHODS

35 healthy volunteers participated in 3 randomized double-blind placebo-controlled studies. In the first 2 studies the short-acting benzodiazepine (LORMetazepam 2 mg), the medium-acting BD (FLUNitrazepam 2 mg) and the long-acting BDs (FLURazepam 30 mg and DIAZepam 10 mg) were administered in single oral doses at bedtime. Hangover was measured in the morning hours prior to administration, and 12, 36, and either 60 h (first study) or 156 h (second study) p.a. The measurements included the pharmaco-EEG, particularly the relative power in the beta band; visual analogue scales for assessing the subjective quality of sleep, EWL-adjective check list; pegboard test and radioreceptor assay. In the third study, a single oral dose of LORM 2 mg was given and the acute sedative effects were measured by the Adaptive Pursuit Tracking Test, Pauli memory test, pegboard and Pursuit Rotor.

RESULTS

The sleep-inducing properties of all BDs could be detected quite clearly on the first night p.a. Distinct hangover effects of LBD were apparent in the pegboard test and residual effects in different beta frequency bands after the first and, to a lesser degree, second nights. Such effects were barely detectable after the SBD. The time course of the RRA plasma levels of LORM and FLUN corresponded well to that of behaviour. The correspondence for DIAZ was less clear. The pharmaco-EEG proved to be the most sensitive measure of benzodiazepine effects, followed by continuous performance measures, such as the pursuit tracking test and driving simulator. Relatively low discriminability was observed with the discontinuous psychomotor tests, such as pegboard. These results have been interpreted within a concept of "activation theory" and it has been concluded that benzodiazepines more likely affect higher central nervous activities, such as the level of vigilance and attention, than simple activities, such as visumotor performance.

Development of tolerance and cross-tolerance to the psychomotor actions of lorazepam and diazepam in man

1 Development of tolerance and cross-tolerance to lorazepam and diazepam in man was assessed in a double-blind and cross-over trial where eight pretrained healthy students volunteered for four 1 week treatment periods started at 1 month intervals. 2 In each period acute psychomotor responses to oral lorazepam 3 mg and diazepam 15 mg were recorded on day 1, as well as on day 8 after 1 week's treatment twice daily with diazepam 5 mg, lorazepam 1 mg, and placebo. At each session several objective psychomotor tests and subjective assessments were done before the drug intake and 1, 2.5, and 4 h after it. 3 In general, the effects of lorazepam were stronger and of longer duration than those of diazepam at the doses used. When comparing the single-dose responses on days 1 and 8, tolerance to lorazepam effects and some cross-tolerance developed on several functions measured. Tolerance but not cross-tolerance developed on choice reaction errors whereas the opposite was found on flicker fusion. No definite tolerance was found on subjective effects. 4 The results tally with an assumption that tolerance to benzodiazepine actions develops at different rates on various parameters measured.

A clinical neuropsychological study of the postoperative course after three types of anaesthesia

In a double-blind study, 57 patients were anaesthetized with either Althesin, thiopentone, or fentanyl combined with diazepam for cystoscopies. One and a half and four hours after the administration of anaesthesia, the patients were investigated with an objective neuropsychological method, continuous Reaction Time, and with a subjective rating scale. Beecher's Mood Scale. One week later the patients answered a questionnaire about side-effects experienced during the days following anaesthesia. At the 1 1/2 h investigation, the patients were cerebrally affected, both subjectively and objectively. The CNS-dysfunction was different for the three anaesthetics. After administration of thiopentone, the patients experienced the highest degree of subjective effects but had the smallest reaction time prolongation. Fentanyl-diazepam gave the least subjective effects, but the highest degree of cerebral affection in the reaction time measurements. The effects of Althesin were intermediate. Four hours after anaesthesia, the reaction time prolongations had disappeared, except for Althesin, and only patients who had thiopentone registered subjective effects. The number of side-effects was greatest and most prolonged following thiopentone. About 25% of the patients reported that side-effects had persisted more than 1 day after anaesthesia.

Anxiety and sedation during a stressful situation after single dose of diazepam versus N-desmethyldiazepam--a controlled trial

Twenty milligram diazepam (DZ) was compared with 20 mg of its main metabolite N-desmethyldiazepam (NDDZ) as single dose, oral premedication in a genuine stressful situation. Fifty patients participated in the randomized, double-blind controlled study. Anxiety and sedation were measured the day before an operation and one hour after premedication, just before the operation. NDDZ was significantly less sedative while the degree of anxiety was rated equal in the two groups. The results may support the hypothesis that a competition between DZ and NDDZ can explain the shift in the effect profile of DZ during long term treatment.