Periodic benzodiazepine antagonist administration prevents benzodiazepine withdrawal symptoms in primates

Low risk of seizures with slow flumazenil infusion and routine anticonvulsant prophylaxis for high-dose benzodiazepine dependence

High-dose benzodiazepine (BZD) dependence represents an emerging and under-reported addiction phenomenon and is associated with reduced quality of life. To date there are no guidelines for the treatment of high-dose BZD withdrawal. Low-dose slow flumazenil infusion was reported to be effective for high-dose BZD detoxification, but there is concern about the risk of convulsions during this treatment. We evaluated the occurrence of seizures in 450 consecutive high-dose BZD dependence patients admitted to our unit from April 2012 to April 2016 for detoxification with low-dose slow subcutaneous infusion of flumazenil associated with routine anticonvulsant prophylaxis. In our sample, 22 patients (4.9%) reported history of convulsions when previously attempting BZD withdrawal. Only four patients (0.9%) had seizures during ( n = 2) or immediately after ( n = 2) flumazenil infusion. The two patients with seizures during flumazenil infusion were poly-drug misusers. The most common antiepileptic drugs (AEDs) used for anticonvulsant prophylaxis were either valproate 1000 mg or levetiracetam 1000 mg. Our data indicate that, when routinely associated with AEDs prophylaxis, low-dose slow subcutaneous flumazenil infusion represents a safe procedure, with low risk of seizure occurrence.

Slow subcutaneous infusion of flumazenil for the treatment of long-term, high-dose benzodiazepine users: a review of 214 cases

Despite the first reports concerning benzodiazepine dependence being published in the early 1960s literature, the risk of benzodiazepine addiction is still greatly debated. The severe discomfort and life threatening complications usually experienced by long-term benzodiazepine users who suddenly interrupt benzodiazepine intake have led to the development of several detoxification protocols. A successful strategy used by our Addiction Unit is abrupt benzodiazepine cessation by administering flumazenil slow subcutaneous infusion (FLU-SSI) with an elastomeric pump. Although some studies proved the efficacy of flumazenil infusion more than 20 years ago, only a few centres in the world offer this method to their patients. This paper reports the data related to 214 subjects addicted to high doses of benzodiazepine and treated with the FLU-SSI method between 2012 and 2014. This technique is less invasive and requires less nursing intervention than intravenous infusion. Our data support FLU-SSI as a possible efficient strategy for the treatment of patients with long-term, high-dose benzodiazepine addiction, and could become a routine therapy as long as the necessary further studies on dose, duration of infusion and safety issues are carried out.

Experimental and clinical evidence for loss of effect (tolerance) during prolonged treatment with antiepileptic drugs

Development of tolerance (i.e., the reduction in response to a drug after repeated administration) is an adaptive response of the body to prolonged exposure to the drug, and tolerance to antiepileptic drugs (AEDs) is no exception. Tolerance develops to some drug effects much more rapidly than to others. The extent of tolerance depends on the drug and individual (genetic?) factors. Tolerance may lead to attenuation of side effects but also to loss of efficacy of AEDs and is reversible after discontinuation of drug treatment. Different experimental approaches are used to study tolerance in laboratory animals. Development of tolerance depends on the experimental model, drug, drug dosage, and duration of treatment, so that a battery of experimental protocols is needed to evaluate fully whether tolerance to effect occurs. Two major types of tolerance are known. Pharmacokinetic (metabolic) tolerance, due to induction of AED-metabolizing enzymes has been shown for most first-generation AEDs, and is easy to overcome by increasing dosage. Pharmacodynamic (functional) tolerance is due to "adaptation" of AED targets (e.g., by loss of receptor sensitivity) and has been shown experimentally for all AEDs that lose activity during prolonged treatment. Functional tolerance may lead to complete loss of AED activity and cross-tolerance to other AEDs. Convincing experimental evidence indicates that almost all first-, second-, and third-generation AEDs lose their antiepileptic activity during prolonged treatment, although to a different extent. Because of diverse confounding factors, detecting tolerance in patients with epilepsy is more difficult but can be done with careful assessment of decline during long-term individual patient response. After excluding confounding factors, tolerance to antiepileptic effect for most modern and old AEDs can be shown in small subgroups of responders by assessing individual or group response. Development of tolerance to the antiepileptic activity of an AED may be an important reason for failure of drug treatment. Knowledge of tolerance to AED effects as a mechanism of drug resistance in previous responders is important for patients, physicians, and scientists.

Flumazenil-precipitated withdrawal in healthy volunteers following repeated diazepam exposure

RATIONALE

Parametric preclinical studies of the benzodiazepine antagonist flumazenil have contributed to the understanding of the physical dependence associated with chronic benzodiazepine use. However, few parametric studies have been conducted in human participants.

OBJECTIVE

This study was designed to assess the effect of duration of benzodiazepine exposure on the intensity of flumazenil-precipitated withdrawal in healthy volunteers.

METHOD

Participants were randomly assigned to receive either oral diazepam (15 mg/70 kg; n=10) or placebo (n=8) capsules nightly for 28 days. Effects of flumazenil (1 mg/70 kg, intravenously administered) were assessed in challenge sessions conducted before capsule ingestion, and after 1, 7, 14, and 28 days of capsule ingestion.

RESULTS

Flumazenil produced a profile of participant-rated effects consistent with benzodiazepine withdrawal that peaked immediately after completion of the 5-min flumazenil injection and rapidly dissipated thereafter. The magnitude of these effects was comparable after 7, 14, and 28 days of diazepam. Flumazenil also produced modest elevations in blood pressure and decreases in skin temperature in the diazepam group, both of which were sustained throughout the approximate 60-min session.

CONCLUSIONS

These findings support previous human research studies indicating that flumazenil precipitates withdrawal after short chronic exposure to benzodiazepines and suggests that duration of exposure does not influence the intensity of withdrawal beyond the first week of exposure.

Principles of drug abuse liability assessment in laboratory animals

This paper describes the rationale for use of preclinical assessments of abuse liability in laboratory animals, and then discusses "cross-cutting" methodological issues that apply to behavioral evaluations intended to contribute to an abuse liability evaluation package. Issues include use of: (1) positive and negative control conditions; (2) full dose-effect evaluations, (3) multiple dependent measures, (4) pharmacokinetic evaluations to guide choice of dose ranges, (5) a species for which good methodological and comparative data are available to aid interpretation of results, and (6) appropriate methods for the group or single-subject experimental design selected. The remainder of the paper describes basic methodology by which three core pieces of behavioral data required by the Food and Drug Administration for its use in the overall abuse liability analysis can be obtained preclinically. Reinforcing effects are assessed in study of drug self-administration; drug discrimination assesses degree of overlap of interoceptive stimulus effects with relevant comparison drugs; physical dependence potential is determined by assessing whether a withdrawal syndrome occurs after chronic drug administration. Background and methodological issues specific to each procedure are discussed. A key consideration for cross-cutting and specific methodological issues is that choices made enable confident interpretation of both positive and negative results.

Intravenous flumazenil versus oxazepam tapering in the treatment of benzodiazepine withdrawal: a randomized, placebo-controlled study

Flumazenil (FLU), a benzodiazepine (BZD) partial agonist with a weak intrinsic activity, was previously found unable to precipitate withdrawal in tolerant subjects submitted to long-lasting BZD treatment. The potential use of FLU to treat BZD withdrawal symptoms has also been evaluated tentatively in clinical studies. In the present experiment, FLU (treatment A) was compared with oxazepam tapering (treatment B) and placebo (treatment C) in the control of BZD withdrawal symptoms in three groups of BZD dependent patients. Group A patients (20) received FLU 1 mg twice a day for 8 days, and oxazepam 30 mg in two divided doses (15 mg + 15 mg) during the first night, oxazepam 15 mg during the second night and oxazepam 7.5 mg during the third night. FLU was injected i.v. in saline for 4 hours in the morning and 4 hours in the afternoon, in association with placebo tablets. Group B patients (20) were treated by tapering of oxazepam dosage (from 120 mg) and with saline solution (as placebo) instead of FLU for 8 days. Group C patients (10) received saline instead of FLU and placebo tablets instead of oxazepam for 8 days. FLU immediately reversed BZD effects on balance task and significantly reduced withdrawal symptoms in comparison with oxazepam and placebo on both self-reported and observer-rated withdrawal scales. The partial agonist also reduced craving scores during the detoxification procedure. In addition, during oxazepam tapering, group B patients experienced paradoxical symptoms that were not apparent in FLU patients. Patients treated with FLU showed a significantly lower relapse rates on days 15, 23 and 30 after the detoxification week. Our data provide further evidence of FLUs ability to counteract BZD effects, control BZD withdrawal and normalize BZD receptor function. The effectiveness of FLU may reflect its capacity to upregulate BZD receptors and to reverse the uncoupling between the recognition sites of BZD and GABA, on the GABA(A) macromolecular complex, that has been reported in tolerant subjects.

Zaleplon and triazolam physical dependence assessed across increasing doses under a once-daily dosing regimen in baboons

The ability of the GABA(A)-receptor-subtype-selective hypnotic zaleplon to produce physical dependence was compared to the nonselective benzodiazepine triazolam. Progressively increasing doses of zaleplon and triazolam were given to baboons by intragastric infusion once each day, with doses increasing every 17 days. Next, the highest dose was given for 10-34 additional days by continuous infusion. Both drugs produced increases in food-maintained lever pressing, ataxia, and time to complete a fine motor task. Plasma levels increased dose-dependently; drug was detectable 24 h after higher doses. Flumazenil produced a mild or intermediate precipitated-withdrawal syndrome on day 14 of all dosing conditions. When drug delivery ended after 85-100 days, a benzodiazepine-type withdrawal syndrome occurred. Physical dependence potential of zaleplon and triazolam appear similar.

Previous experience of diazepam withdrawal prevents the formation of a withdrawal-conditioned taste aversion: test of a blocking hypothesis

Prior experience of withdrawal from chronic diazepam treatment reduces the aversiveness of withdrawal when precipitated withdrawal is made the unconditioned stimulus in a conditioned taste aversion (CTA) paradigm. Accounts of the mechanism by which unconditioned stimulus pre-exposure reduces its effectiveness in CTA postulate that unconditioned stimulus pre-exposure leads to the formation of associations with the environment, resulting in blocking of taste conditioning. We tested whether a blocking explanation accounted for the reduced effectiveness of withdrawal as a unconditioned stimulus in a CTA following prior exposure. Mice received chronic diazepam (15mg/kg/day, s.c. in sesame oil), or sesame oil vehicle, for three periods of 7 days, interspersed with 3-day withdrawal periods. The first two withdrawals occurred either in the home cage, or in one compartment of a place-conditioning apparatus (PCA). Animals which experienced withdrawal in the home cage were given equivalent experience of the PCA outside the withdrawal period. The third withdrawal was precipitated by i.p. administration of flumazenil (20mg/kg). Thirty minutes before injection, all animals were placed individually in the compartment of the PCA to which they had been previously exposed, allowed to drink a novel 10% sucrose solution, injected with flumazenil, and replaced in the PCA for 2 h, before being returned to the home cage. When sucrose consumption was measured 24 h later, only that group which had experienced all three withdrawals in the PCA showed evidence of a CTA. These animals (but not those that had experienced withdrawal in the home cage, or vehicle-treated mice) also showed strong avoidance of the chamber in which they had experienced withdrawal. Thus, no evidence was adduced that prior conditioning of an environment-conditioned stimulus to a withdrawal unconditioned stimulus blocked the formation of a CTA. When the CTA conditioning was repeated in the home cage, again only the mice that had experienced withdrawal in the place-conditioning apparatus showed evidence of conditioning. These observations are discussed in the context of blocking explanations of unconditioned stimulus pre-exposure.

Previous experience of withdrawal from chronic diazepam ameliorates the aversiveness of precipitated withdrawal and reduces withdrawal-induced c-fos expression in nucleus accumbens

Flumazenil (20 mg/kg, i.p.)-precipitated withdrawal from chronic treatment with diazepam (DZP, 15 mg/kg, s.c. in sesame oil for 21 days) resulted in a decreased seizure threshold to the convulsant, pentylenetetrazole (PTZ), infused into the tail vein; withdrawal from 21-day chronic diazepam treatment, interspersed with two periods of drug withdrawal, resulted in a greater decrease in convulsant threshold. A separate experiment showed that consumption of a sucrose solution immediately prior to precipitated withdrawal resulted in a decreased subsequent consumption of the sucrose solution; no such evidence of a conditioned taste aversion (CTA) was seen in mice given prior experience of withdrawal. Thus, prior experience of withdrawal enhanced the effects of a subsequent precipitated withdrawal in increasing seizure sensitivity, but weakened the ability of this withdrawal to serve as an aversive unconditioned stimulus (US). The weakening of the aversive properties of precipitated withdrawal may reflect habituation to the withdrawal stimulus, and was accompanied by a loss of the ability of withdrawal to induce c-fos expression in the shell of the nucleus accumbens, an area sensitive to both novel, and stressful, as well as rewarding stimuli.

Induction of partial epileptic seizures by flumazenil

PURPOSE

This study addressed the efficacy of flumazenil (FMZ) to induce or activate interictal or ictal epileptic discharges in patients with medically intractable partial epilepsies.

METHODS

Flumazenil, 1 mg, was injected intravenously in 67 patients undergoing presurgical monitoring for epilepsy surgery, 49 of whom had been treated with benzodiazepines (BZDs) before flumazenil was given. Continuous video electroencephalogram (EEG) monitoring with surface or intracranial electrodes was used to evaluate interictal EEG activity, ictal discharges, and the occurrence and semiology of clinically manifest epileptic seizures.

RESULTS

Interictal epileptiform potentials did not change in frequency or distribution after FMZ. In patients not pretreated with BZDs, epileptic seizures could not be provoked. In eight of the 49 patients pretreated with BZDs, epileptic seizures occurred within 30 min of FMZ application. Seizure semiology and regional EEG onset were identical to seizures recorded without FMZ. Patients operated on according to seizure-onset localization with FMZ had a >75% reduction in seizure frequency or became seizure free.

CONCLUSIONS

Seizure induction by FMZ seems to be a valid method for evaluating seizure semiology and localization of the seizure-onset zone during presurgical monitoring of patients with medically intractable localization-related epilepsies.

Progesterone withdrawal. II: insensitivity to the sedative effects of a benzodiazepine

Previous results from this lab have demonstrated that the GABA-modulatory steroid 3alpha-OH-5alpha-pregnan-20-one (3alpha, 5alpha-THP) exhibits withdrawal properties, increasing anxiety [M.A. Gallo, S.S. Smith, Progesterone withdrawal decreases latency to and increases duration of electrified prod burial: a possible rat model of PMS anxiety, Pharmacol. Biochem. 46 (1993) 897-904.] and seizure susceptibility [S.S. Smith, Q.H. Gong, F.-C. Hsu, R.S. Markowitz, J. M.H. ffrench-Mullen, X. Li, GABAA receptor alpha4 subunit suppression prevents withdrawal properties of an endogenous steroid, Nature 392 (1998) 926-930.] upon abrupt discontinuation after chronic administration of its parent compound, progesterone (P), in a manner similar to other GABA-modulatory drugs. Further, we have demonstrated that withdrawal from P produces insensitivity to the potentiating effects of the benzodiazepine (BDZ) lorazepam (LZM) on GABA-gated Cl- current [A.-M.N. Costa, K.T. Spence, S.S. Smith, J.M. H. ffrench-Mullen, Withdrawal from the endogenous steroid progesterone results in GABAA currents insensitive to BDZ modulation in rats CA1 hippocampus, J. Neurophysiology 74 (1995) 464-469; S.S. Smith, Q.H. Gong, F.-C. Hsu, R.S. Markowitz, J.M.H. ffrench-Mullen, X. Li, GABAA receptor alpha4 subunit suppression prevents withdrawal properties of an endogenous steroid, Nature 392 (1998) 926-930.], assessed using whole cell patch clamp procedures on pyramidal neurons acutely dissociated from CA1 hippocampus. The purpose of the present study was to examine the withdrawal effects of P on the sedative potency of LZM, tested behaviorally as the ability to maintain position on a variable speed treadmill following LZM administration (0.75 mg/kg). Both continuous (continuous release P capsule, single withdrawal) as well as discontinuous (multiple P injection, multiple withdrawal) paradigms were tested. Longer continuous release paradigms were more effective in abolishing the sedative effects of LZM, without producing a change in baseline response. The LZM insensitivity observed following the multiple withdrawal paradigm was prevented by prior intraventricular administration of antisense oligonucleotide against the alpha4 subunit of the GABAA receptor. These results support the hypothesis that withdrawal from P decreases the behavioral response to LZM as a direct result of increases in the alpha4 subunit of the GABAA receptor. Withdrawal from P occurs endogenously during pre-menstrual and post-partum periods, when decreased response to BDZ has been reported.

Diazepam-treated female rats: flumazenil- and PK 11195-induced withdrawal in the hippocampus CA1

Six female rats had a loading dose of 180 mg of diazepam (DZ) contained in two Silastic capsules implanted in their backs. Thereafter, a single 90-mg capsule was implanted weekly for 4 weeks prior to weekly microinjections of 1 microl of flumazenil (6.25, 12.5, or 25 microg) and PK 11195 (3.125, 6.25, or 12.5 microg) or vehicle into the CA1. Three control rats had empty capsules implanted but received only the high dose of flumazenil after 5 weeks. The time of DZ exposure spanned 8 weeks. Mean steady-state plasma levels of DZ were 1.06 +/- 0.11, and the mean total (DZ + metabolites) was 2.46 microg/ml +/- 0.37. Flumazenil elicited a dose-related precipitated withdrawal score (PAS) in DZ-treated rats (but not in controls) characterized by dose-related increases in convulsive (twitches and jerks), motor and autonomic signs, dose-related increases in the percent of total power in the low frequency (1-4 Hz), and decreases in the high-frequency (18-26 Hz) bands of the EEG recorded from the dentate and the amygdala. PK 11195 produced a dose-related increase in the 4-12 Hz band of the EEG recorded from the CA1, whereas the PAS was mild and not dose-related. However, the 6.25 and 12.5-microg doses elicited a significant PAS that tended to increase with dose. These data indicate that chronic DZ produces dependence, and that in the CA1 it involves the participation of central and possibly peripheral benzodiazepine (BZ) receptors located within this structure.

Withdrawal from 3alpha-OH-5alpha-pregnan-20-One using a pseudopregnancy model alters the kinetics of hippocampal GABAA-gated current and increases the GABAA receptor alpha4 subunit in association with increased anxiety

In the present study, we have characterized properties of steroid withdrawal using a pseudopregnant rat model. This paradigm results in increased production of endogenous progesterone from ovarian sources and as such is a useful physiological model. "Withdrawal" from progesterone induced by ovariectomy on day 12 of pseudopregnancy resulted in increased anxiety, as determined by a decrease in open arm entries on the elevated plus maze compared to control rats and pseudopregnant animals not undergoing withdrawal. Similar findings were obtained 24 hr after administration of a 5alpha-reductase blocker to a pseudopregnant animal, suggesting that it is the GABAA-modulatory 3alpha-OH-5alpha-pregnan-20-one (3alpha, 5alpha-THP) that produces anxiogenic withdrawal symptoms. Twenty-four hours after steroid withdrawal, the time constant for decay of GABAA-gated current was also reduced sixfold, assessed using whole- cell patch-clamp procedures on pyramidal neurons acutely dissociated from CA1 hippocampus. Thus, 3alpha,5alpha-THP withdrawal results in a marked decrease in total GABAA current, a possible mechanism for its anxiogenic, proconvulsant sequelae. In addition, 3alpha,5alpha-THP withdrawal resulted in insensitivity to the normally potentiating effect of the benzodiazepine lorazepam (LZM) on GABAA-gated Cl- current. This withdrawal profile is similar to that reported for other GABAA-modulatory drugs such as the benzodiazepines (BDZs), barbiturates, and ethanol. These changes were also associated with significant two and threefold increases in both the mRNA and protein for the alpha4 subunit of the GABAA receptor, respectively, in hippocampus. The pseudopregnancy paradigm may be a useful model for periods of endogenous 3alpha,5alpha-THP withdrawal such as premenstrual syndrome and postpartum or postmenopausal dysphoria, when increased emotional lability and BDZ insensitivity have been reported.

Discriminative stimulus effects of flumazenil in rhesus monkeys treated chronically with chlordiazepoxide

Discriminative stimulus effects of the benzodiazepine antagonist flumazenil were studied in two rhesus monkeys receiving 3.2 mg/kg/12 h of chlordiazepoxide while discriminating between vehicle and 0.056 mg/kg of flumazenil. In a drug discrimination component responding was maintained under a FR 10 schedule of stimulus-shock termination; in a non-discrimination component responding was maintained under a FR 10 schedule of food presentation. Flumazenil and Ro 15-4513 occasioned >80% flumazenil-lever responding at doses larger than 0.032 and 0.056 mg/kg, respectively. Pentylenetetrazole, ethyl-beta-carboline-3-carboxylate (betaCCE), ketamine and spiradoline failed to substitute for flumazenil although >80% drug-lever responding was observed for two of the compounds in one monkey. Flumazenil, Ro 15-4513, pentylenetetrazole, betaCCE but not ketamine or spiradoline decreased rates of responding in the food component at doses that had little effect on rates in the stimulus-shock termination component. When chlordiazepoxide injections were discontinued and saline was administered before the session, monkeys did not respond on the flumazenil lever; when flumazenil was administered under the same conditions, monkeys responded on the flumazenil lever despite not having received chlordiazepoxide for nine days. Drug stimulus control was established with flumazenil in monkeys receiving chlordiazepoxide and substitution studies suggest that this effect of flumazenil might result from antagonist actions at benzodiazepine receptors: however, lack of withdrawal-related effects after termination of chlordiazepoxide treatment precludes validation of this procedure for studying benzodiazepine dependence.

Basic aspects of GABA-transmission in alcoholism, with particular reference to GABA-transaminase

Neuronal dysfunction is the neurobiological basis for alcoholic behaviour, and ethanol craving seems related to hypofunction of the GABA-ergic activity. Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the central nervous system (CNS). In several studies, GABA has been shown to be an important target of ethanol in the CNS, partly, as a consequence of damage to membrane-bound enzymes and receptors. GABA is involved in mediating pre- and post-synaptic inhibition of neuronal activity. It is speculated that the initial excitatory effects of ethanol may be due to inhibition of GABA-ergic activity whereas the sedative effects of the higher doses may be mediated by the activation of this inhibitory system. In the CNS, GABA is synthesised from glutamic acid by the enzyme glutamate decarboxylase (GAD) and catabolized into succinic semialdehyde by the enzyme GABA-transaminase (GABA-T), which are pyridoxal phosphate (PLP) dependent enzymes. Platelet GABA-T was characterized as being similar to central GABA-T. Inhibition of GABA-T with certain potent and selective compounds markedly increases the levels of brain GABA. Experimentally, acute ethanol treatment does not alter GABA-T activity whereas chronic treatment produces an increase in the activity, though, with some reservations since a bimodal effect has been found in chronically ethanol-treated rats. Thus, as it will be discussed below, it may be suggested that GABA-T inhibitors (e.g. vigabatrin) could have a potential role in the treatment of alcoholism and in some of the problems of ethanol withdrawal and of other drugs of abuse. Related studies on metabolism and concentrations of GABA are also promising and show a greater increase in our understanding of the aetiology and treatment of ethanol dependence and withdrawal. In general, this article also reviews both the animal and clinical observations in the field of alcoholism with regard to the GABA system.

Ro 15-4513 alteration of pentobarbital dependence

This study investigated the ability of the benzodiazepine inverse agonist, Ro 15-4513, to alter the expression of physical dependence on pentobarbital. Male Sprague-Dawley rats were made physically dependent on pentobarbital by continuous. IP, infusion of escalating doses of pentobarbital for 12 days. In Experiment 1, pentobarbital dependent rats received either vehicle or Ro 15-4513, in doses of 5, 10, or 15 mg/kg, IP, periodically during the pentobarbital abstinence period. As expected, Ro 15-4513 produced a significant, dose-dependent, exacerbation of withdrawal signs in the pentobarbital dependent rats. In Experiment 2, either vehicle or Ro 15-4513, at a dose of 15 mg/ kg, was administered, IP, once daily during the 12 days of continuous pentobarbital infusion. During the subsequent pentobarbital abstinence period it was noted that the withdrawal signs were significantly reduced in the rats receiving the daily administration of Ro 15-4513. It is hypothesized that the benzodiazepine inverse agonist, Ro 15-4513, may inhibit the development of physical dependence on pentobarbital through an opposing action on the GABA-A receptor.

Reversal of triazolam- and zolpidem-induced memory impairment by flumazenil

The effects of flumazenil, a benzodiazepine receptor antagonist, on triazolam- and zolpidem-induced memory impairment were investigated. Sixty subjects received oral triazolam 0.5 mg, zolpidem 20.0 mg, or placebo at 10 a.m. (n = 20 per drug). Ninety minutes later, half of the subjects (n = 10) in each oral drug group were administered flumazenil 1.0 mg, while the remaining half received placebo (normal saline), through indwelling venous catheters. Learning/memory tests (including Simulated Escape, Restricted Reminding, Paired-Associates, and Repeated Acquisition) were administered at that time, and at 1.5-h intervals over the next 6 h. Triazolam/placebo and zolpidem/placebo drug combinations impaired memory on all tests (all Ps < 0.05). However, the triazolam/flumazenil and zolpidem/flumazenil groups showed no evidence of impairment during any test session. These results demonstrate that flumazenil 1.0 mg rapidly and lastingly reverses memory impairment caused by agonists of the benzodiazepine receptor. Furthermore, nonsignificant trends suggested that performance of the placebo/flumazenil group was consistently better than that of the placebo/placebo group, denoting a possible role of endogenous benzodiazepine agonists in natural sleep/wake processes.

Precipitated withdrawal in squirrel monkeys after repeated daily oral administration of alprazolam, diazepam, flunitrazepam or oxazepam

The lowest dose of alprazolam, diazepam, flunitrazepam and oxazepam consistently to induce loss of righting reflex in squirrel monkeys or vehicle was orally administered to monkeys on 18 consecutive days: 2 mg/kg alprazolam (n = 4), 30 mg/kg diazepam (n = 4), 1 mg/kg flunitrazepam (n = 4), 280 mg/kg oxazepam (n = 5), or vehicle (n = 4). Tolerance developed rapidly for loss of righting reflex, more slowly for sleep and only minimally for muscle relaxation observed during the period immediately following daily oral administration. Injection of the specific benzodiazepine receptor antagonist flumazenil (10 mg/kg i.v.) 5 h after the ninth daily oral treatment produced signs of precipitated withdrawal (tremor, vomiting and/or convulsions) in one alprazolam-, four diazepam-, one flunitrazepam- and four oxazepam-treated monkeys, but not in the vehicle-treated monkeys. Physiological saline injected intravenously several days later under these same experimental conditions failed to provoke a precipitated withdrawal reaction. When flumazenil-induced precipitated withdrawal was again evaluated after the 18th daily oral treatment, withdrawal signs were observed in all alprazolam- and all diazepam-treated monkeys, as well as in three flunitrazepam- and three oxazepam-treated monkeys, but not in the vehicle-treated monkeys (convulsions were observed in one alprazolam-, two diazepam-, one flunitrazepam- and two oxazepam-treated monkeys). No signs of spontaneous withdrawal were observed in any of the monkeys during a subsequent 3-week drug-free period. Thus, repeated administration of approximately equieffective doses of these four benzodiazepines resulted in a similar development of tolerance and physical dependence (indicated by the occurrence of a precipitated withdrawal reaction).

Current benzodiazepine issues

This article deals with some of the recent evidence bearing on the issues of the liability of benzodiazepines to lead to abuse, dependence, and adverse behavioral effects. Reviews of epidemiological, clinical and experimental literature indicated that the previous conclusion about abuse of these drugs still holds: the vast majority of the use of benzodiazepines is appropriate. Problems of nonmedical use arise nearly exclusively among people who abuse other drugs. Nevertheless, there are reasons for concern about patients who take benzodiazepines regularly for long periods of time. These drugs can produce physiological dependence when taken chronically, and although this does not appear to result in dose escalation or other evidence of "psychological dependence," physiological dependence can result in patient discomfort if drug use is abruptly discontinued. Also, physicians are currently prescribing shorter-acting benzodiazepines in preference to longer-acting benzodiazepines. The shorter-acting drugs can produce a more intense withdrawal syndrome following chronic administration. Furthermore, rates of use of benzodiazepines increase with age, and elderly patients are more likely than younger ones to take the drug chronically. The clearest adverse effect of benzodiazepines is impairment of memory. This, too, may be particular concern in older patients whose recall in the absence of drug is typically impaired relative to younger individuals, and who are more compromised following drug administration.

Different kinetics of tolerance to behavioral and electroencephalographic effects of chlordiazepoxide in the rat

The daily oral administration of chlordiazepoxide (40 mg/kg) over 9 weeks in rats elicited full tolerance to muscle relaxant effects within 7 weeks, as revealed by twice weekly evaluations of abdominal tone myorelaxation and decreased grip strength. No full tolerance was achieved, however, during the 9 weeks of treatment in terms of ataxia. Electroencephalographic (EEG) studies showed that this tolerance to the behavioural effects was accompanied by a progressive decrease in mean power spectra, associated with a progressive decrease in the beta band, but in this case, full tolerance was reached within 4 weeks. Once weekly evaluations of the ability of chlordiazepoxide to protect the animals against pentylenetetrazole seizures revealed a similar pattern. Treatment with flumazenil (50 mg/kg p.o.) 24 h after the last chlordiazepoxide administration induced a clear withdrawal syndrome associated with EEG changes which consisted of an increase in total power spectra associated with an increase in the delta band (in comparison with chlordiazepoxide-dependent rats not given the antagonist). These findings suggest that the different kinetics of the tolerance to anticonvulsant and EEG effects in comparison to myorelaxant effects can be attributed to a different involvement of benzodiazepine receptor subtypes.

Biological processes in benzodiazepine dependence

The indications for the benzodiazepines include anxiety, insomnia, muscle spasm and epilepsy and each disorder has a variety of biological substrates. Limbic structures and the neurotransmitters noradrenaline, 5-HT and GABA have all been implicated. Benzodiazepines act on allosteric receptor sites and potentiate the actions of GABA in modulating chloride ionophores across nerve membranes. These effects can be blocked by the benzodiazepine antagonist, flumazenil. The molecular pharmacology of the benzodiazepine-GABA-chloride receptor is complex, with a wide range of different subunits. Animal models of dependence have suggested that the changes associated with long-term benzodiazepine use are related more to receptor-effector coupling than to the receptor characteristics themselves. Thus, benzodiazepine agonists on long-term use lose their efficacy, antagonists become partial inverse antagonists, and inverse agonists increase in efficacy. Various clinical implications are explored, including the use of flumazenil to prevent and to treat benzodiazepine withdrawal syndromes.

Flumazenil induces localised increases in glucose utilization during diazepam withdrawal in rats

The quantitative [14C]2-deoxyglucose autoradiographic technique has been employed to identify the neural circuits involved in diazepam withdrawal. Local cerebral glucose utilization (LCGU) was assessed in parallel groups of rats chronically treated with diazepam (5 mg/kg i.p., daily for 28 days), in rats that were withdrawn from chronic diazepam 24 h previously and in those that received flumazenil (5 mg/kg i.v.) immediately or 24 h after the last dose of diazepam. Two further groups received chronic vehicle or acute flumazenil (5 mg/kg i.v.). Rats withdrawn from diazepam 24 h previously did not produce changes in LCGU in the 51 structures examined compared with both control and chronic diazepam treated groups, suggesting that spontaneous withdrawal from small doses of diazepam does not evoke marked alterations in functional activity. In contrast, flumazenil-precipitated diazepam withdrawal produced a marked increase in glucose use in structures of the Papez circuit of emotion (mammillary body, anterior thalamus, cingulate cortex), together with increases in the septal nucleus, basolateral amygdala and nucleus accumbens. Less widespread increases in glucose use occurred in primary auditory and visual areas and in extrapyramidal areas. This pattern resembles that produced after acute FG-7142 administration (Brain Res., 475 (1988) 218-231). In rats receiving flumazenil 24 h after the last dose of diazepam there was a similar, but more restricted, pattern of change in LCGU. Flumazenil had no effect on LCGU in drug naive rats. Thus, flumazenil could only exert an effect upon LCGU in rats chronically treated with diazepam. These data provide functional neuroanatomical evidence for a withdrawal shift in the inverse agonist direction after chronic diazepam and suggest that flumazenil-precipitated withdrawal changes may merely be a reflection of this phenomenon.

A pilot study of the effects of flumazenil on symptoms persisting after benzodiazepine withdrawal

The potential of the benzodiazepine antagonist flumazenil (Ro 15-1788) to lessen persisting benzodiazepine withdrawal symptoms was demonstrated in 11 patients who had been drug free for between 1 month and 5 years. Doses ranging from 0.2 to 2.0 mg divided into three intravenous injections over a few hours relieved long-standing symptoms to varying extents. These included clouded thinking, tiredness, muscular symptoms such as neck tension, cramps and shaking and the characteristic perceptual symptoms of benzodiazepine withdrawal, namely, pins and needles, burning skin, pain and subjective sensations of bodily distortion. Mood disorder, when present, also improved but the reduction in anxiety and depression may have reflected relief of physical symptoms. The onset of maximum response was sometimes delayed by as much as a day but was usually prompt. Side effects were reported to be either absent or typically described as lightheadedness or dizziness, lasted only a few minutes and were usually well tolerated. The benefits last between a few hours and several days despite flumazenil's otherwise short duration of action. However, symptoms did return to varying degrees in most cases, suggesting the need for repeated doses.

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.

Neuroadaptive responses to chronic ethanol

Cellular responses of neuronal tissue to chronic ethanol exposure are reviewed. Evidence for adaptive responses to the acute actions of ethanol is available for five systems: GABA-activated chloride channels, voltage-sensitive calcium channels, NMDA-activated cation channels, receptors coupled through stimulatory guanine nucleotide binding proteins, and membrane lipid order. We suggest that at least some of these adaptive responses occur because of ethanol actions at the level of gene expression.

The effect of intravenous flumazenil on interictal electroencephalographic epileptic activity: results of a placebo-controlled study

The effect on interictal electroencephalographic epileptic activity of intravenous flumazenil (Ro 15-1788), a benzodiazepine antagonist and potential antiepileptic drug, was studied in 10 patients. Comparison was made with intravenous diazepam (10 mg) and placebo using a single-blind, single-dose, cross-over design. A dose of 3 mg flumazenil was well tolerated and produced a significantly greater reduction in the number of epileptic transients during the first 40 minutes after injection than did placebo (p less than 0.05). This effect was similar to that of diazepam in magnitude and duration. When flumazenil (3 mg) was administered immediately after intravenous diazepam (10 mg), the reduction in interictal epileptic activity was not significantly different from that produced by diazepam alone. The results suggest that either flumazenil has intrinsic antiepileptic activity and in this respect acts as a partial agonist at the benzodiazepine receptor, or that it is antagonising an endogenous proconvulsant ligand in these patients.

Lack of effect of a small dose of flumazenil in reversing short-term tolerance to benzodiazepines in normal subjects

Twelve normal volunteers received two courses of 7 days of either lorazepam (2 mg every morning; six subjects) or oxazepam (30 mg every morning; six subjects). After one of the courses, 0.2 mg of flumazenil was injected, after the other placebo, using a balanced design and double-blind procedures. A test dose of the lorazepam or oxazepam was administered the day after the flumazenil or placebo. A battery of physiological and psychological tests was applied before and after the dose of benzodiazepine on days 1, 4, 8 and 10. The benzodiazepines had the expected effects on the EEG, and event-related potentials (ERP), impaired several psychological tests and induced drowsiness and relaxation. Some tolerance was seen with respect to anxiolytic effects, some EEG and ERP variables and some psychological tests, but not those of memory. Tolerance tended to be more apparent in the subjects given lorazepam than in the oxazepam-treated subjects. No effects of the small dose of flumazenil in reversing tolerance were apparent.

Cyclopyrrolones, unlike some benzodiazepines, do not induce physical dependence in mice

In a model of physical dependence in mice, treatment with cyclopyrrolones such as zopiclone and suriclone (from 4 to 400 mg/kg/day), did not modify the sensitivity of the gamma-aminobutyric acid (GABA) receptor complex to the partial inverse agonist FG 7142 following their withdrawal, whereas sensitivity changes were observed after treatment and withdrawal from some benzodiazepines (e.g. lorazepam, diazepam, flunitrazepam and triazolam). These data suggest that, in contrast to some benzodiazepines, zopiclone and suriclone may not produce physical dependence.

Effects of the 5-HT3 antagonist GR38032F (ondansetron) on benzodiazepine withdrawal in rats

Effects of the 5-HT3 receptor antagonist GR38032F (ondansetron) on chlordiazepoxide withdrawal were assessed in rats which received chlordiazepoxide b.i.d. for 21 days at doses up to 40 mg/kg per injection. Withdrawal signs recorded were: body weight and food intake, which fell and then recovered over 9 days. Saline or GR38032F (1.0, 0.1 or 0.01 mg/kg) were administered b.i.d. during withdrawal. Clear withdrawal signs were seen in rats treated with saline after chronic chlordiazepoxide. However, GR38032F at 0.1 mg/kg reduced the severity of withdrawal. At 0.01 mg/kg GR38032F shortened withdrawal duration, but did not diminish peak withdrawal signs. At 1.0 mg/kg GR38032F, did not attenuate withdrawal signs at all. GR38032F (0.01-1.0 mg/kg) had no effect on ad lib food intake, therefore the attenuation of withdrawal was probably not simply due to stimulation of appetite. These data support recent claims that GR38032F attenuates benzodiazepine withdrawal, and they indicate that this effect shows an inverted U-shaped dose-response curve.

The history of benzodiazepine dependence: a review of animal studies

This article provides a historical review of the animal literature relating to the development of tolerance to the behavioral effects of benzodiazepines, and the incidence of biochemical and behavioral changes that result from termination of benzodiazepine treatment (spontaneous withdrawal responses). It charts the slow emergence of a pertinent animal literature and highlights conclusions that were prevalent in 1963 (at the introduction of diazepam), 1973 (at the introduction of lorazepam), 1980 and the present day. For 25 years the animal literature has lagged behind the clinical literature, but recent studies into the neurochemical mechanisms of benzodiazepine dependence and possible treatments for withdrawal responses suggest that, at last, animal experiments may be about to make a substantial contribution.

Acute opioid physical dependence in humans: effect of naloxone at 6 and 24 hours postmorphine

Previous studies in our laboratory have documented the occurrence of naloxone-precipitated opioid abstinence from 45 minutes to 6 hours after acute morphine administration in humans. This study extended the morphine-naloxone interval to 24 hours and examined the effect of repeated naloxone challenges on withdrawal responses. Six male nondependent opiate users participated in eight experimental sessions in which they received single IM injections of morphine (18 mg/70 kg) followed 6 and 24 hours later by challenge sessions with IM placebo or naloxone (10 mg/70 kg). Naloxone challenge at 6 hours postmorphine reversed morphine-induced miosis and subjective reports of opiate symptoms, drug high, good drug effects, and drug liking. At 24 hours postmorphine, naloxone had no effect on these measures, which had returned to premorphine levels. However, at 6 and 24 hours postmorphine, naloxone precipitated subjective symptoms and observer-rated signs of opioid abstinence. When naloxone challenge at 24 hours was preceded by naloxone at 6 hours postmorphine, the magnitude of abstinence symptoms and signs was attenuated. These data suggest that morphine-induced adaptational changes underlying the development of physical dependence persist beyond other measureable agonist effects, and that these changes are disrupted or reversed by repeated antagonist administration.

Development of tolerance to clobazam in fully kindled rats: effects of intermittent flumazenil administration

The effects of acute and chronic treatment with the 1,5-benzodiazepine, clobazam, were studied on fully kindled amygdaloid seizures in rats. After acute dosing, clobazam significantly reduced all parameters of kindled seizures (seizure severity, seizure duration, duration of amygdalar afterdischarges) at doses of 7.5 or 10 mg/kg i.p. 'Active' plasma concentrations of clobazam ranged between 300-800 ng/ml. The elimination half-life of clobazam in plasma was about 1 h. Only very low (10-75 ng/ml) levels of the major metabolite, N-desmethylclobazam, were detected in rats. Administration of N-desmethylclobazam indicated that plasma concentrations of at least 300 ng/ml were necessary for anticonvulsant effects. During chronic administration of clobazam, 10 mg/kg 3 times daily, marked tolerance developed to the anticonvulsant and adverse (ataxiogenic and sedative) effects of the benzodiazepine. The experiment was repeated using a different protocol with minimized environmental stimuli and no amygdala stimulation during chronic clobazam administration. The loss of effects on seizure severity and motor function was similar to the first chronic experiment, whereas the loss of effects on seizure and afterdischarge duration was less marked. This indicates that conditioning of 'learned tolerance' is partly involved in clobazam tolerance in kindled rats. Intermittent injection of the benzodiazepine receptor antagonist, flumazenil, 5 mg/kg i.p. every third day, did not alter the loss of pharmacodynamic effects during chronic treatment with clobazam, but seemed to prevent hyperexcitation and other abstinence symptoms in the withdrawal period. The data indicate that periodic injection of a benzodiazepine receptor antagonist does not represent a possible therapeutic approach for preventing the development of tolerance during long-term benzodiazepine exposure.

The pharmacology of human anxiety

The human pharmacology of anxiety disorders, including panic disorder, is detailed. The major theories center around the role of benzodiazepine receptor, noradrenergic and serotonergic dysfunction. The contribution that challenge tests with lactate, hyper- and hypocapnia, beta- and alpha-2-adrenoceptor agonists, peptides, pentylenetetrazol, and caffeine make to our understanding of the biological basis of anxiety and these major theories are described and discussed.

Pharmacological mechanisms of benzodiazepine withdrawal

The pharmacology of the benzodiazepine receptor is unusual in relation to other receptors in that there exist three types of ligand: agonists (e.g. diazepam), which are anxiolytic and anticonvulsant; antagonists (e.g. flumazenil), which are neutral; and inverse agonists (e.g. FG 7142), which are anxiogenic and proconvulsant. Chronic administration of agonists leads to tolerance and withdrawal, and produces a global shift in benzodiazepine receptor function with attenuation of agonist and enhancement of inverse agonist actions. These changes appear without alterations in receptor number or affinity, and may reflect a shift in efficacy, "withdrawal shift", at the receptor. Treatment with flumazenil during benzodiazepine agonist administration, or even in the period after the last dose, can prevent or reverse this efficacy shift as indicated by a lack of sensitization to inverse agonists. The clinical implications of these findings are discussed.

A theory of benzodiazepine dependence that can explain whether flumazenil will enhance or reverse the phenomena

Repeated administration of benzodiazepines (BDZs) produces dependence in man and animals and this is reflected in the phenomena of tolerance and withdrawal responses. In BDZ-dependent animals the BDZ-receptor antagonist flumazenil (Ro 15-1788) reverses the increased anxiety and decreased seizure threshold seen when benzodiazepine treatment is withdrawn. In contrast are reports that flumaenil enhances BDZ-withdrawal responses. Indirect influences on the direction of flumazenil's effects on anxiety are the duration and dose of BDZ treatment, whether tolerance has developed to its anxiolytic effect and whether there is an anxiogenic response on drug withdrawal. However, we conclude that the crucial factor is the anxiety level of the animal: when this is high flumazenil becomes anxiolytic; when this is low flumazenil is anxiogenic. These bidirectional effects of flumazenil can be seen in drug-naive and BDZ-dependent animals. We propose a theory of benzodiazepine dependence that can account for anxiogenic responses on drug withdrawal and for flumazenil's bidirectional effects; central to this theory is the assumption that flumazenil normalises the benzodiazepine receptor, returning it to a baseline state. Thus it is whether an animal's score lies above or below this baseline that will determine the direction of flumazenil's effect. The clinical implications of this theory are discussed. We suggest that during the development of benzodiazepine dependence, two independent adaptive biochemical mechanisms are triggered: one underlying the development of tolerance to the anxiolytic responses, the other underlying the incidence of increased anxiety on drug withdrawal. It is only changes in the latter that are induced by the administration of flumazenil.

Chronic exposure to Ro 15-1788: differential effect on flunitrazepam binding to cortex and hippocampus

The time course of changes in specific [3H]flunitrazepam binding following 2 weeks of treatment with the benzodiazepine antagonist Ro 15-1788 (2.7 and 4 mg/kg per day in drinking water) was studied in the rat neocortical and hippocampal synaptosomal membranes. Such a treatment produced regional increases in the density of benzodiazepine sites, which remained for up to 24 and 48 h after drug withdrawal in the hippocampus and cortex, respectively; the dissociation constant (Kd) was unchanged. In addition, a significant reduction in GABA enhanced [3H]flunitrazepam binding to cortical, but not to hippocampal, membranes from Ro 15-1788-treated animals was found 72 h after drug withdrawal. These data show that there is a regional difference in responses of the GABA/benzodiazepine receptor complex following chronic in vivo exposure to Ro 15-1788 and that, beside the increases in the maximal binding (Bmax) of [3H]flunitrazepam the coupling between the GABA and the benzodiazepine recognition sites was also affected.

Relationship of agonist efficacy to changes in GABA sensitivity and anticonvulsant tolerance following chronic benzodiazepine ligand exposure

Benzodiazepine ligands of differing efficacy including the agonist, diazepam, the partial agonist, Ro 16-6028 and the antagonist, Ro 15-1788, were administered in vivo to rats continuously for 3 weeks. The magnitude of change in various measures of GABA sensitivity could be correlated directly with increasing agonist efficacy: maximal changes were seen following chronic treatment with diazepam, intermediate changes were seen following the partial agonist Ro 16-6028 and no changes were observed following chronic Ro 15-1788 administration. The magnitude of change could also be correlated with increasing potential for tolerance development to anticonvulsant efficacy following chronic exposure to these benzodiazepine ligands.

Behavioral differentiation of benzodiazepine ligands after repeated administration in baboons

Baboons received repeated daily administration of saline, 5.6 mg/kg midazolam, 5.0 mg/kg flumazenil (Ro15-1788), 3.2 mg/kg 3-carboethoxy-beta-carboline hydrochloride (beta CCE) or 10 mg/kg beta CCE for 5 days. Behavioral signs of sedation and excitation were scored for 1 h after i.m. injections. Daily administration of these benzodiazepine-receptor ligands differentiated their behavioral effects; repeated midazolam resulted in tolerance to the sedative and ataxic effects; repeated beta CCE resulted in sensitization to its convulsant properties; and repeated flumazenil or saline produced no changes in behavior. In a second study, baboons received repeated injections of midazolam (5.6, 11.2 or 20 mg/kg per day) for 6 days. All three groups became tolerant to the sedative and ataxic effects of midazolam. Acute injections of flumazenil (5.0 mg/kg) on day 5 produced a dose-dependent withdrawal syndrome. This flumazenil treatment produced a slight attenuation in the degree of tolerance to midazolam on day 6, suggesting that receptor sensitivity to the benzodiazepine agonist may have partially reset.

Intermittent naloxone attenuates the development of physical dependence on methadone in rhesus monkeys

Rhesus monkeys that received 15 daily injections of methadone (2 mg/kg i.m.) exhibited a characteristic opiate withdrawal syndrome after injection of naloxone (0.5 mg/kg i.m.) on the 16th day. In comparison, injection of naloxone (0.5 mg/kg i.m.) once every 2 days during a similar 15 day methadone treatment period in these same monkeys significantly attenuated the severity of the opiate withdrawal syndrome exhibited after naloxone injection on the 16th day. Each naloxone administration during the 15 day methadone treatment period elicited an opiate withdrawal syndrome that did not significantly differ on each of the 7 days it was given and was less severe than the syndrome precipitated by naloxone following 15 days of methadone without intermittent naloxone. The lack of increments in the withdrawal response to the seven naloxone injections during the 15 days of methadone treatment and the attenuation of the withdrawal response to naloxone on day 16 after intermittent naloxone administration during the 15 day methadone treatment period support the hypothesis that naloxone modifies opiate receptor mechanisms so that they revert to an agonist-naive state following antagonist exposure. These findings suggest that various agonist and antagonist opiate drug combinations or mixed agonist-antagonist drug could be clinically useful in the management of situations where physical dependence on opiates is a problem.

Flumazenil but not nitrendipine reverses the increased anxiety during ethanol withdrawal in the rat

After 7 day's gradual introduction of ethanol, rats were maintained for a further 4 weeks on a liquid diet containing 10% ethanol (mean daily dose 11.8 +/- 0.2 g/kg/day). Control-treated rats received liquid diet alone. Pairs of rats were tested in the social interaction test of anxiety 8 h after withdrawal. Withdrawal from ethanol significantly reduced the time spent in social interaction compared with controls, indicating an anxiogenic withdrawal response. Nitrendipine (50 mg/kg) had no effect on, whereas flumazenil (4 mg/kg) significantly reversed, this withdrawal response. This reversal appeared to be long-lasting as there was still no evidence of increased anxiety when rats were again withdrawn after 3 more days of ethanol diet.

Effects of beta-carboline-ethyl ester on plasma corticosterone--a parallel with antagonist-precipitated diazepam withdrawal

Diazepam has been shown to produce physical dependence based on observations of behavioral stimulation or, in our laboratory, by increases in plasma corticosterone (CS) during antagonist-precipitated withdrawal. The behavioral excitation appears similar to that observed following the administration of beta-carboline esters--agents reported to interact with benzodiazepine receptors and termed "inverse agonists." The focus of the present study is to correlate the occurrence of changes in CS with behavioral excitation previously observed by others. Further, these studies are designed to show a parallel between the manifestations of benzodiazepine withdrawal and the pharmacologic effects of beta-carboline ethyl ester. Experiments were done in conscious unrestrained male Sprague-Dawley rats, with chronic i.v. catheters, using sound-attenuated one-way vision boxes. These studies compared the hormonal and behavioral changes induced by beta-carboline ethyl ester (beta CCE) with CGS-8216-precipitated withdrawal in rats treated with diazepam for 8 days. Rats treated chronically with diazepam (5 mg/kg/day), showed a significant increase in plasma (CS) following CGS-8216. Behavioral abstinence scores were also significantly elevated. beta CCE (0.5-5.0 mg/kg) showed a significant dose-related increase in plasma CS. Behavioral scores were also increased at doses of 0.5 and 2.0 mg/kg. beta CCE-induced plasma CS increases were antagonized by CGS-8216 at doses of 1.0 and 2.0 mg/kg but not by 0.5 mg/kg. In animals chronically treated with diazepam, beta CCE evoked a more prolonged plasma CS elevation than in vehicle-treated animals suggesting a dual agonist/antagonist effect. These data suggest a parallel between CS elevations and behavioral effects during withdrawal as well as similarities between the action of beta CCE and the manifestations of this withdrawal.

Flumazenil prevents the development of chlordiazepoxide withdrawal in rats tested in the social interaction test of anxiety

Rats were chronically treated with chlordiazepoxide (CDP 10 mg/kg/day) or vehicle for 27 days. Twenty-four hours after their last dose, they received flumazenil (4 mg/kg) or vehicle and were tested in the social interaction test, in a low-light, familiar arena. CDP withdrawal significantly reduced the time spent in social interaction compared with controls, indicating an anxiogenic withdrawal response. This was completely reversed by flumazenil. A second group received CDP for 27 days and, in addition, received a single dose of flumazenil (4 mg/kg) 6 days before testing. Flumazenil prevented the development of the anxiogenic withdrawal response in these rats.

The abstinence syndrome in diazepam-dependent cats is precipitated by Ro 15-1788 and Ro 15-4513 but not by the benzodiazepine receptor antagonist ZK 93426

Diazepam-dependent cats were challenged with different benzodiazepine recognition site ligands 24 h after the last dose of chronic treatment with diazepam (7 mg/kg, i.p. at 08.00 and 20.00 h, for 21 consecutive days). The benzodiazepine derivatives Ro 15-4513 (a partial inverse agonist) and Ro 15-1788 (a pure antagonist), precipitated an abstinence syndrome within minutes after i.p. administration. Abstinence signs included tremors, increased muscle tone, irritability, fear, pupillary dilation and vocalizations. On the contrary, the beta-carboline derivatives ZK 93426 (an antagonist) and FG 7142 (a partial inverse agonist) failed to precipitate abstinence signs in diazepam-dependent cats when given at doses that prevented the acute effects of diazepam. Our results demonstrate that the ability to induce withdrawal signs in diazepam-dependent cats strongly depends on the benzodiazepine structure of the challenge drug since beta-carboline antagonist and partial inverse agonists lack this property.

Rapid induction of lorazepam dependence and reversal with flumazenil

Benzodiazepine tolerance, dependence and withdrawal are well established clinical entities although the pharmacological basis for these are still unclear. Recent data suggest that the primary event may be a change in efficacy at the benzodiazepine receptor. The present study demonstrates the rapid development of tolerance and dependence to lorazepam, defines its pharmacology in more detail, and shows that it may be rapidly reversed by treatment with the benzodiazepine antagonist flumazenil. These observations argue in favour of a receptor efficacy change underlying benzodiazepine tolerance and withdrawal and suggest a potential pharmacological treatment for this common and disabling clinical problem.