Pharmacodynamic interaction between midazolam and a specific benzodiazepine antagonist in humans

Blood concentrations of midazolam in status epilepticus using an appropriate condition of HPLC

BACKGROUND

The aim of the present study was to determine an index to evaluate the efficacy and safety of midazolam (MDZ) to treat status epilepticus (SE). An original system was therefore developed to measure blood concentrations of MDZ and 1-hydroxymidazolam (1-OHMDZ) as the main metabolite on high-performance liquid chromatography.

METHODS

This system was established through inspection of chromatograms, calibration curves and coefficient of correlations of MDZ. The clinical course of 11 SE patients, ranging from 4 months to 10 years of age, are described. These patients were treated with MDZ and measured at each blood concentration of MDZ. Moreover, patients were evaluated on cranial computed tomography and magnetic resonance imaging and video electroencephalogram (EEG), and it was determined that their seizures disappeared in accordance with the disappearance of convulsions and interictal EEG findings.

RESULTS

Reproducibility was good with this system. The standard curves of MDZ and 1-OHMDZ were almost straight, and the correlation coefficients of MDZ and 1-OHMDZ were r = 0.9999 and r = 0.9998, respectively. The convulsions in nine of 11 SE patients disappeared without side-effects and the blood concentrations of MDZ in all the patients were measured. The mean peak blood concentrations of MDZ and 1-OHMDZ were higher than those reported in other studies.

CONCLUSIONS

The clinical utility of this system has been demonstrated. An index to evaluate the efficacy and safety of MDZ is necessary, and MDZ blood concentrations measured on the present original precise measuring system could help in establishing a plan to successfully treat SE.

A randomised crossover trial of post-operative cognitive and psychomotor recovery from benzodiazepine sedation: effects of reversal with flumazenil over a prolonged recovery period

OBJECTIVE

To study the post-operative cognitive and psychomotor recovery from midazolam conscious sedation, after reversal with the benzodiazepine antagonist flumazenil over a prolonged recovery period.

DESIGN

A prospective, double-blind, randomised, crossover trial.

SETTING

Out-patient Sedation Department, Newcastle Dental Hospital and School

METHOD

Eighteen patients, ASA I or II, received midazolam on two separate occasions to undergo equivalent dental treatment. Following treatment patients were reversed with intravenous flumazenil or saline (placebo) at alternate appointments. Assessment of mood and cognitive function was undertaken using a highly sensitive and specific computerised battery of cognitive tests administered by telephone. Cognitive and psychomotor tests were administered prior to sedation and every hour for 6 hours post reversal.

RESULTS

Results indicated no significant effect of flumazenil on simple reaction time and choice reaction time but did show a trend of reversing the effects of midazolam on numeric working memory and word recognition.

CONCLUSION

The cognitive and psychomotor effects of the sedation were not fully reversed by flumazenil. Cognitive impairments were still present up to 6 hours post-reversal, despite patients appearing clinically more alert. This has important implications for treatment protocols and discharge instructions.

Clinical neuropharmacology of drugs of abuse: a comparison of drug-discrimination and subject-report measures

Advances in molecular pharmacology and behavioral science have helped elucidate the structure and function of the central nervous system and its relationship to behavior and has sparked the development of pharmacological agents that have increasingly selective and potent effects with fewer adverse side effects. The sensitivity and predictive validity of the two most commonly used methodologies for assessing the neuropharmacological effects of centrally active drugs, subject report of drug effects and drug discrimination, were examined. The sensitivity of the measures was comparable across stimulant, sedative, and opioid drugs. Results with drug-discrimination methodologies were generally consistent with hypothesized neuropharmacological mechanisms across all drug classes, whereas subject reports conformed under more limited testing conditions. Firm conclusions regarding the relative utility of drug-discrimination and subject-report measures for clinical studies of neuropharmacological mechanisms are limited by the small number of studies in which the two methodologies have been tested using identical pharmacological pretreatment manipulations.

The effect of intravenous administration of variable-dose flumazenil after fixed-dose ketamine and midazolam in healthy cats

The effects of intravenous administration of variable-dose flumazenil (0, 0.001, 0.005, 0.01, and 0.1 mg/kg) after ketamine (3 mg/kg) and midazolam (0.0 and 0.5 mg/kg) were studied in 18 healthy unmedicated cats from time of administration until full recovery. End-points were chosen to determine whether flumazenil shortened the recovery period and/or modified behaviors previously identified and attributed to midazolam. Overall, flumazenil administration had little effect on recovery or behaviors. One minute after flumazenil administration, all cats were recumbent but a greater proportion of cats which received the highest dose assumed sternal recumbency with head up than any other group. Although not significant, those cats that received the highest flumazenil dose also had shorter mean times for each of the initial recovery stages (lateral recumbency with head up, sternal recumbency with head up and walking with ataxia) than any of the other treatment groups that received midazolam. For complete recovery, flumazenil did decrease the proportion of the cats that was sedated, but did not shorten the time to walking without ataxia. Based on this study, the administration of flumazenil in veterinary practice, at the doses studied, to shorten and/or improve the recovery from ketamine and midazolam in healthy cats cannot be recommended.

Clinical pharmacology of midazolam in infants and children

Midazolam is a parenteral benzodiazepine with sedative, amnesic, anxiolytic, muscle relaxant and anticonvulsant properties. The drug exerts its clinical effect by binding to a receptor complex which facilitates the action of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). Midazolam has a faster onset and shorter duration of action than other benzodiazepines such as diazepam and lorazepam. The most serious adverse events associated with midazolam in children include hypoventilation, decreased oxygen saturation, apnoea and hypotension. It is water soluble in the commercially prepared formulation but becomes lipid soluble at physiological pH and can then cross the blood brain barrier. It is metabolised in the liver by the cytochrome P450 system, and its chief metabolite is 1-hydroxymethyl midazolam. The latter is conjugated to the glucuronide form, and it has only minimal biological activity. Midazolam is excreted primarily by the kidney. Its half-life in children over 12 months is reported to be 0.8 to 1.8 hours, with a clearance of 4.7 to 19.7 ml/min/kg. Doses given to children must be calculated on a mg/kg basis. For children 6 months to 5 years of age the initial dose is 0.05 to 0.1 mg/kg. A total dose up to 0.6 mg/kg titrated slowly may be necessary to achieve the desired endpoint. For children 6 to 12 years of age the initial dose is 0.025 to 0.05 mg/kg with a total dose up to 0.4 mg/kg to achieve the desired end-point.

Pharmacology of flumazenil

Flumazenil, an imidazobenzodiazepine, is the first benzodiazepine antagonist available for clinical use. It is a specific competitive antagonist at benzodiazepine receptors, which are associated with receptors for gamma-aminobutyric acid, the most important inhibitory neurotransmitter in the central nervous system. Administered orally, it has a low bioavailability and the preferred route is intravenous. Its usual clinical role is to reverse the effects of benzodiazepine sedation; however, administered before, or with, other benzodiazepines, it modifies their effects, the extent of such modification depending on the dose, duration of effect and relative receptor affinity of the agonist. Flumazenil also reverses adverse physiological effects of benzodiazepines. Its indications include reversal of benzodiazepine-induced sedation, termination of benzodiazepine-induced anaesthesia, return of spontaneous respiration and consciousness in intensive care patients and the treatment of paradoxical reactions to benzodiazepines. Other potential indications include its use in hepatic encephalopathy, alcohol intoxication and coma; however, these claims still require substantiation. Following sedation reversed with flumazenil, minimal residual effects of the agonist can sometimes be detected using psychomotor tests and are due to the relatively short half-life of flumazenil, but are of no clinical consequence. There is concern that flumazenil could precipitate an acute withdrawal syndrome following long-term benzodiazepine administration; however, the available evidence suggests otherwise and that it could be useful in the treatment of benzodiazepine tolerance. The existence of flumazenil is important, with implications for future research and the development of minimally invasive therapy and day-case surgery. With increasing pressures on non-anaesthetically trained practitioners to perform sedation, flumazenil has important implications for safety.

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.

An assessment of resedation following flumazenil-induced antagonism of intravenous midazolam: comparison of psychomotor and amnesic recovery with a non-sedated reference group

The specific benzodiazepine antagonist flumazenil can enhance patient recovery following local anaesthetic day-case surgery performed under sedation. However, in view of its short elimination half-life, concerns have been expressed about the risk of resedation following its use. An open, randomised, parallel group study was designed to explore this question. Eighty-five patients were studied. Group A (n=43) patients underwent local anaesthetic cystoscopy with intravenous (i.v.) midazolam sedation. Following cystoscopy, and 30 min after the injection of midazolam, a bolus dose of flumazenil (0.5 mg i.v.) was given. Group B (n=42) patients underwent no operation and received no drugs but, in all other respects, were treated in an identical fashion to patients in group A. Tests of psychomotor function and memory were administered at baseline and again at 0.5, 1, 2, 3 and 4 h (or equivalent times for group B patients) following the injection of flumazenil. The test results showed no evidence of resedation, but there was evidence of incomplete reversal, as shown by significant differences in critical flicker fusion and delayed word recall at the 0.5-h test point. Group B patients showed no evidence of practice effects but did demonstrate an impairment in test performance possibly related to motivational factors. In conclusion, this study provides no evidence of resedation when using flumazenil to reverse the acute effects of midazolam. Incomplete reversal of amnesia need not delay patient discharge but has important implications with respect to the timing and nature of information imparted to patients prior to their release from hospital.

Flumazenil exerts intrinsic activity on sleep EEG and nocturnal hormone secretion in normal controls

The physiological function of benzodiazepine (BDZ) receptors includes regulation of sleep and neuroendocrine activity. Most of the pharmacological effects of BDZ are blocked by flumazenil. However, recent neurological and behavioral studies suggest that flumazenil has its own central intrinsic activity. This issue was addressed in a study of the sleep EEG and the nocturnal secretion of growth hormone and cortisol in ten normal male controls, who were given flumazenil either alone or in combination with the BDZ agonist midazolam, placebo and midazolam alone. Flumazenil prompted an increase in sleep onset latency, a decrease in slow wave sleep and an increase in wakefulness. Plasma cortisol concentrations after flumazenil administration were lower than after midazolam. Both flumazenil and midazolam decreased nocturnal growth hormone secretion. After simultaneous application of both BDZ receptor ligands the growth hormone blunting was amplified. Our study demonstrates that at the level of the sleep EEG and neuroendocrine activity flumazenil is capable of exerting both agonistic and inverse agonistic or antagonistic effects.

Equivalent dipoles of FFT data visualize drug interaction at benzodiazepine receptors

The aim of the present investigation was to study if the benzodiazepine receptor antagonist flumazenil could reverse the effects on the brain electrical activity induced by the benzodiazepine receptor agonist midazolam. The method of FFT approximation was used for this purpose. It allows the calculation of center of gravity equivalent dipoles of spectral EEG data. The results are reference independent and allow therefore a more unambiguous interpretation compared to conventional FFT data reports. Twelve subjects were investigated before and after 0.1 mg/kg and 0.2 mg/kg midazolam respectively, directly and 4 h after administration of 1 mg flumazenil. Our results imply that the application of flumazenil after midazolam sedation leads to an almost complete restoration of the brain electrical activity. However, especially in the beta frequencies above 20 Hz differences in depth of equivalent dipoles were found directly after flumazenil application as well as 4 h later. This could suggest that neuronal generators in different brain structures were responsible for the electrical activity after flumazenil administration compared to before.

Electroencephalogram effect measures and relationships between pharmacokinetics and pharmacodynamics of centrally acting drugs

Electroencephalogram (EEG) effect parameters may be useful in pharmacokinetic-pharmacodynamic modelling studies of drug effects on the central nervous system (CNS). Effect parameters derived from a quantitative analysis of the EEG appear to be perfectly suited to characterise the relationships between pharmacokinetics and pharmacodynamics of benzodiazepines and intravenous anaesthetics. EEG parameters represent many of the characteristics of ideal pharmacodynamic measures, being continuous, objective, sensitive and reproducible. These features provide the opportunity to derive concentration-effect relationships for these drugs in individuals, which yield important quantitative information on the potency and intrinsic efficacy of these drugs. The EEG techniques presented can be used to study the influences of factors such as age, disease, chronic drug use and drug interactions on the concentration-effect relationships of psychotropic drugs. An important issue is the choice of the EEG parameter to characterise the CNS effects of the compounds. More attention must be paid to evaluating the relevance of EEG parameters to the pharmacological effects of the drugs. Knowledge of the relationship between EEG effect parameters and clinical effects of drugs under different physiological and pathophysiological conditions is crucial to determining the value of EEG parameters in drug effect monitoring. Pharmacodynamic parameters derived from the concentration-EEG effect relationship may be correlated to pharmacodynamic parameters obtained from other in vitro and in vivo effect measurements. These comparisons revealed that changes in the amplitudes in the beta frequency band of EEG signals is a relevant measure of pharmacological effect intensity of benzodiazepines, which reflects their affinity and intrinsic efficacy at the central gamma-aminobutyric acid (GABA) benzodiazepine receptor complex. The exact EEG correlates of the anxiolytic, anticonvulsant, sedative and hypnotic actions of benzodiazepines have not yet clearly been elucidated. For intravenous anaesthetics, close correlations between the potency determined with EEG measurements and clinical measures of anaesthetic depth have been established, suggesting that, in principle, EEG parameters can adequately reflect depth of anaesthesia. However, more study is required to further substantiate these findings.

Sedation in Neonatal and Pediatric Intensive Care

Despite the widespread use of potent sedative and analgesic agents in adult patients, it is remarkable that systemic analgesia and sedation have not been administered routinely to neonates and children until very recently. Adequate sedation and analgesia have historically been withheld from these patients because of the mistaken beliefs that pain perception was not fully developed and that these patients were much more prone to adverse effects of the most commonly used agents. There is now overwhelming evidence that pain perception and physiologic responses to stress are present in neonates of all gestational ages and a variety of effective sedative/analgesic agents have recently been added to the therapeutic armamentarium. We will outline the classes of agents currently available, briefly describe mechanisms of action and the relevant pharmacokinetic—pharmacodynamic parameters, summarize the short-term and long-term side effects following prolonged administration of these agents, and highlight practical considerations for the most commonly used sedative-analgesic medications.

Flumazenil. A reappraisal of its pharmacological properties and therapeutic efficacy as a benzodiazepine antagonist

Flumazenil is a specific benzodiazepine antagonist which is indicated when the central effects of a benzodiazepine need to be attenuated or terminated. Following intravenous administration of up to 1 mg, flumazenil effectively reverses sedation and improves psychomotor performance following administration of short and longer acting benzodiazepines used for sedation, or general anaesthesia supplemented with benzodiazepines. The duration of action is short at generally 30 to 60 minutes and supplemental doses of flumazenil may be needed to maintain the desired level of consciousness in some patients. After poisoning with high dosages of benzodiazepines alone or combined with other drugs, the initial single dose of flumazenil will require supplementing with repeated low intravenous doses or an infusion to maintain wakefulness. In such patients, flumazenil also facilitates differential diagnosis and reduces the necessity for interventions. Flumazenil thus enhances recovery and allows more rapid discharge of patients sedated with benzodiazepines for diagnostic procedures and facilitates management of patients during the initial recovery period following general anaesthesia supplemented with benzodiazepines, but does not preclude normal monitoring during the recovery period. Flumazenil is clearly very useful in treating drug poisoning when benzodiazepines are a major component. By virtue of its specific benzodiazepine antagonist effects, flumazenil provides an innovative and well tolerated approach in clinical situations requiring rapid reversal of benzodiazepine-induced central nervous system depressant effects.

Benzodiazepine poisoning. Clinical and pharmacological considerations and treatment

Benzodiazepines are among the most frequently prescribed drugs worldwide. This popularity is based not only on their efficacy but also on their remarkable safety. Pure benzodiazepine overdoses usually induce a mild to moderate central nervous system depression; deep coma requiring assisted ventilation is rare, and should prompt a search for other toxic substances. The severity of the CNS depression is influenced by the dose, the age of the patient and his or her clinical status prior to the ingestion, and the coingestion of other CNS depressants. In severe overdoses, benzodiazepines can occasionally induce cardiovascular and pulmonary toxicity, but deaths resulting from pure benzodiazepine overdoses are rare. Quantitative determinations of benzodiazepines are not useful in the clinical management of intoxicated patients since there is no correlation between serum concentrations and pharmacological and toxicological effects. Benzodiazepine overdoses occurring during pregnancy rarely induce serious morbidity in mothers or fetuses, although large doses administered near delivery can induce respiratory depression in neonates. The teratogenic potential of benzodiazepines remains controversial, but is probably small if it exists at all. There is clear evidence that the prolonged use of even therapeutic doses of benzodiazepines will lead to dependence. The risk of developing significant withdrawal symptoms is related to dosage and duration of treatment. Prevention of gastrointestinal absorption should be initiated in all intentional benzodiazepine overdoses. Forced diuresis and dialysis techniques are not indicated since they will not significantly accelerate the elimination of these agents. Intravenous administration of flumazenil, a pure benzodiazepine antagonist, effectively reverses benzodiazepine-induced CNS depression.

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.

Intraocular pressure in anaesthetized dogs given flumazenil with and without prior administration of midazolam

This study examined the effect of flumazenil, a benzodiazepine antagonist, on aqueous humour pressure in dogs receiving either midazolam or no benzodiazepine. Twenty-four halothane-anaesthetized dogs were assigned to one of four groups. Group I (n = 6) received saline iv at 0, 45 and 90 min. Group 2 (n = 6) received saline at 0 min, flumazenil 0.0025 mg.kg-1 iv at 45 min and flumazenil 0.16 mg.kg-1 at 90 min. Group 3 (n = 6) received midazolam 1.6 mg.kg-1 at 0 min followed by continuous iv infusion (1.25 mg.kg-1.hr-1). Flumazenil was given at 45 and 90 min as in Group 2. In Group 4 (n = 6) aqueous humour pressure was elevated to about 35 mmHg then midazolam and flumazenil were given as in Group 3. Aqueous humour pressure was determined using a 30-gauge needle placed into the anterior chamber. Saline or flumazenil produced no change in aqueous humour pressure in Groups 1 and 2. In Groups 3 and 4, midazolam decreased aqueous humour pressure from 18 +/- 2 mmHg (mean +/- SD) to 14 +/- 3 mmHg (P less than 0.001) and from 34 +/- 5 mmHg to 31 +/- 3 mmHg (P less than 0.01) respectively. Flumazenil given during continuous infusion of midazolam produced increases of aqueous humour pressure of 2 +/- 1 (P less than 0.01) to 5 +/- 2 mmHg (P less than 0.01) that lasted less than or equal to 12 min. It is concluded that at both normal and elevated aqueous humour pressures flumazenil produces statistically significant but clinically unimportant increases of aqueous humour pressure in anaesthetized dogs receiving midazolam, but not in dogs given no benzodiazepine.

Flumazenil: a new benzodiazepine antagonist

Flumazenil is a recently discovered pharmacologic antagonist of the CNS effects of benzodiazepines. It acts by binding CNS benzodiazepine receptors and competitively blocking benzodiazepine activation of inhibitory GABAergic synapses. Animal studies and some human studies appear to demonstrate that flumazenil has weak intrinsic agonist activity; on the other hand, studies are inconclusive in demonstrating any inverse agonist effects of this agent. Evidence available suggests that flumazenil is well tolerated in human beings over a broad range of doses when given either orally or parenterally and does not produce serious adverse effects. In the setting of isolated benzodiazepine overdose, flumazenil is capable of completely reversing coma within one to two minutes, with this effect lasting between one and five hours. Repeat doses can be given safely to reverse recurrent effects of longer-acting benzodiazepines. Flumazenil is undergoing further evaluation by the Food and Drug Administration; should this drug receive approval, it is likely to be used in emergency departments as well as in a variety of other clinical settings. First, it could be used to effect rapid reversal of benzodiazepine-induced sedation that has been administered to facilitate medical, orthopedic, and surgical procedures, particularly in the event of inadvertent respiratory depression. Second, flumazenil might have a therapeutic role in the management of patients who have taken benzodiazepine overdoses. Although most of these patients can be managed successfully with supportive therapy alone, it is possible that the use of flumazenil may obviate the need for intubation and respiratory support in such patients and eliminate the possible adverse effects of even short-term endotracheal intubation. Finally, flumazenil could have both diagnostic and therapeutic value in patients with acute alterations of mental status of unknown etiology, particularly when possible drug overdose is a consideration. Because flumazenil appears to be specific in its antagonism of benzodiazepine-induced respiratory and CNS depression, it could be used empirically to confirm or exclude a role of benzodiazepines in the generation of mental status changes in the setting of overdose or coma of unknown origin. This in turn might obviate the need for further expensive (eg, computed tomography) and sometimes invasive (eg, lumbar puncture) diagnostic modalities. This might be particularly useful because there is nothing about benzodiazepine-induced coma that clearly distinguishes it from other causes of coma; thus, there are no signs or symptoms that may reasonably allow benzodiazepine overdose to be confirmed or eliminated on clinical grounds. Further studies will continue to define the ultimate use of this new agent.

Postoperative analgesic requirements following flumazenil administration

The effect of flumazenil (RO 15-1788) on postoperative analgesic requirements was evaluated in 30 postoperative patients. This prospective investigation was a double-blind, placebo-controlled trial in patients undergoing general anesthesia supplemented by midazolam and fentanyl or sufentanil. Patients received either flumazenil (n = 20) or placebo (n = 10) by random assignment. Analgesic requirements were measured in morphine equivalents (MEs) and were recorded for a three-hour period following the administration of flumazenil. All patients received the assigned treatment within five minutes of arrival to the postanesthesia room. Total ME requirements were 4.1 +/- 3.8 mg for the flumazenil group and 4.5 +/- 4.6 mg (p = 0.71) for the placebo group. Patient analgesic requirements were also assessed when patients were adequately alert. For the flumazenil group this time period was 6.2 +/- 12.7 minutes versus 52.9 +/- 28.4 minutes for placebo (p less than 0.01). MEs (flumazenil 4.1 +/- 3.8 mg vs. placebo 3.7 +/- 3.2 mg) were not significantly different (p = 0.57) when similar levels of consciousness were compared. The onset of pain was more rapid with flumazenil patients as evidenced by the first analgesic dose at 15.7 +/- 25.1 minutes for the flumazenil group versus 34.7 +/- 43.7 for the placebo group; however, these data were not statistically different (p = 0.144). These results suggest that flumazenil does not increase postoperative analgesic requirements during the immediate postanesthesia period; however, patients receiving flumazenil may experience an earlier onset of postoperative pain.

Flumazenil: a benzodiazepine antagonist

Although benzodiazepines have been proven safe and effective for the induction and maintenance of sedation, some instances require the reversal of these events prior to the natural process of metabolism and elimination. Flumazenil, a 1,4-imidazobenzodiazepine, is an antagonist that can reduce or terminate benzodiazepine effects in a dose-dependent manner. The antagonist acts by the competitive inhibition of benzodiazepines at their central nervous system receptor sites. When administered intravenously in incremental doses, flumazenil allows for optimal patient response on an individual basis. Despite its short elimination half-life, small doses of flumazenil are usually effective in producing benzodiazepine reversal. Flumazenil's short duration of activity is due to its rapid hepatic metabolism and elimination. Intravenous antagonist doses of 0.2 mg followed by 0.1 mg/min to a total dose of 1 mg have produced significant results in reversing benzodiazepine sedation. As much as 5 mg of flumazenil have been necessary when treating benzodiazepine or mixed-agent intoxications. In such situations, response rarely exceeds a duration of one hour. If resedation occurs, additional doses or an infusion of the antagonist may provide the desired response. Flumazenil is well tolerated locally as well as systemically. Nausea and vomiting occurring after anesthesia is the most documented adverse effect in both placebo and treatment populations. However, there has been no significant difference in the occurrence of vomiting in placebo compared with flumazenil-treated subjects. Careful observation and slow reversal of central nervous system depression is crucial in the avoidance of benzodiazepine withdrawal in those patients dependent upon these agents. Flumazenil appears to provide a mechanism for the safe and effective reversal of benzodiazepine-induced sedation.(ABSTRACT TRUNCATED AT 250 WORDS)

Possible interaction of fluoroquinolones with the benzodiazepine-GABAA-receptor complex

1. The possible involvement of the benzodiazepine (BZD)-GABAA-receptor complex in mediating CNS stimulatory effects of fluoroquinolones was tested in vitro, in a binding inhibition assay and in vivo, in a clinical drug interaction study using electro-encephalogram (EEG) monitoring. 2. The specific binding of [3H]-flunitrazepam to rat synaptic brain membranes was inhibited by various fluoroquinolones in a concentration-dependent manner. 3. Ofloxacin had CNS-stimulating effects as revealed by the EEG which were slightly augmented by flumazenil but reversed by coadministration of midazolam. 4. In conclusion, our findings suggest that clinically observed CNS adverse effects of fluoroquinolones could be mediated at least in part through interaction with the BZD-GABAA-receptor complex and may be controlled by BZD agonist administration.

The effects of flumazenil-precipitated abstinence on the pharmacokinetics of chronic oxazepam in dogs

The pharmacokinetics of oxazepam was studied in naive dogs and in oxazepam-dependent dogs without and with administered flumazenil (6 mg/kg). Oxazepam is eliminated with a relatively short elimination half life (ca. 150 min) in both acutely and chronically treated dogs. It exhibits only a modest first pass metabolism (ca. 10%) and its bioavailability following oral administration is about 22%. The steady state concentration of oxazepam in chronically treated dogs was lower than was predicted from single dose studies. Flumazenil did not change the rate of absorption or elimination of oxazepam-dependent dogs. The total steady state plasma concentration of oxazepam was significantly reduced by flumazenil administration suggesting a displacement interaction between flumazenil and oxazepam.

A benzodiazepine receptor antagonist improves emergence of mice from halothane anaesthesia

The benzodiazepine receptor antagonist, flumazenil, at a dose of 10 mg/kg given intraperitoneally to mice, had no effect on the minimum air concentration (MAC-50) of halothane causing anesthesia in 50% of the animals and which was 1.0% by volume of the inhaled air. Diazepam, 10 mg/kg, potentiated the effect of halothane. When the mice had been pretreated with diazepam and flumazenil, 10 mg/kg or 20 mg/kg, partial but not complete reversal of the potentiating effect of diazepam was observed, minimum air concentration values being 0.6% after diazepam alone and 0.8% after diazepam and flumazenil. However, mice pretreated intraperitoneally with flumazenil, in the concentration range 1-10 mg/kg, delivered as a solution in polyethylene glycol-Intralipid vehicle or as a suspension in saline, recovered control levels of spontaneous motor activity much faster than in the absence of flumazenil, on emergence from halothane-induced anaesthesia. In this range, the effect was not dose-dependent. These findings suggest that some of the effects of halothane are mediated at the level of the benzodiazepine receptor.

Effects of the benzodiazepine antagonist flumazenil on postoperative performance following total intravenous anaesthesia with midazolam and alfentanil

Postoperative performance following total intravenous anaesthesia (TIVA) using midazolam and alfentanil was studied with and without the administration of a single dose of a benzodiazepine antagonist, flumazenil (Ro 15-1788). Performance was compared with a reference group anaesthetized with thiopentone, alfentanil and nitrous oxide. All patients were assessed by use of a rating scale which took into account the degree of sedation, amnesia, comprehension and cooperation as well as temporal and spatial orientation. There was a slow recovery following TIVA with somnolence and amnesia lasting several hours. Administration of flumazenil 1.0 mg i.v. at extubation caused a significant reduction of sedation (P less than 0.001) during the first postoperative hour, with patients fully awake or only lightly sedated, but was later followed by resedation. The patients of the reference group were moderately sedated during the observation period. Five and six hours postoperatively there was no difference between the groups. Amnesia was more profound in the groups that received midazolam; the effect of the antagonist could only be seen for 15 min after its administration. Comprehension and cooperation, as well as orientation, were equally good in the antagonist and in the reference group during the immediate postoperative period, whereas in the TIVA group a gradual improvement over the first hours was seen. In the antagonist group there was no increase in the number of analgesic requirements, no anxiety attacks or other adverse effects. It is concluded that flumazenil offers an improvement in postoperative performance following TIVA induced by midazolam and alfentanil, but the effects are of short duration.

Lack of effect of the benzodiazepine antagonist flumazenil (Ro 15-1788) on the performance of healthy subjects during experimentally induced ethanol intoxication

Flumazenil is a specific benzodiazepine antagonist. This study was designed to determine whether it also reverses CNS depression due to acute alcohol intoxication. Intoxication was experimentally induced in 6 healthy volunteers by intravenous infusion of ethanol. Individual constant ethanol plasma concentrations in the range 1.47 +/- 0.04 g.l-1 to 1.71 +/- 0.03 g.l-1 were maintained over 6 h. Two doses of flumazenil (0.1 or 0.2 mg.kg-1) and placebo were administered intravenously in a randomized, double-blind, two-way cross-over fashion. A battery of psychometric tests and subjective ratings of mood and performance were performed at baseline and at regular intervals during the study. Before the administration of flumazenil the characteristic symptoms and signs of ethanol intoxication were present in all subjects. Performance (measured by visual analogue scales), reaction time, digit symbol substitution test, and a tracing test, were markedly impaired by ethanol. After the injection of flumazenil three volunteers reported some subjective improvement in performance. However, in none of the subjects was there a difference between either dose of flumazenil and placebo in terms of an improvement in the objective psychometric variables.

Flumazenil. A preliminary review of its benzodiazepine antagonist properties, intrinsic activity and therapeutic use

Flumazenil, a 1,4-imidazobenzodiazepine, is a specific benzodiazepine antagonist which is indicated for use when the effect of a benzodiazepine must be quickly attenuated or terminated. Following intravenous administration, the onset of clinically apparent benzodiazepine antagonism usually occurs within 1 to 5 minutes. Although flumazenil has a short elimination half-life of about 1 hour, a single intravenous dose of up to 1 mg is usually sufficient to attain and maintain for about 2 hours the desired level of consciousness after general anaesthesia or conscious to moderate sedation induced by benzodiazepines. After intoxication with high doses of benzodiazepines the initial single dose of flumazenil will require supplementing with repeated low intravenous doses or an infusion (0.1 mg/h) to maintain a state of wakefulness. Flumazenil is well tolerated, and since it reliably attenuates or reverses the central effects of benzodiazepines and is specific for these drugs, it facilitates diagnosis by eliminating benzodiazepine intoxication in patients in whom the cause of unconsciousness is unknown. While results of some studies suggested that flumazanil may have intrinsic benzodiazepine partial agonist or inverse agonist activity, this is unlikely to be clinically important with usual doses. Thus, flumazenil is a very promising, effective, short acting benzodiazepine antagonist which is well tolerated by most patients. Undoubtedly, its full clinical potential has yet to be realised.

Specific treatment of benzodiazepine overdose

Intentional benzodiazepine (BZD) overdose is usually a benign condition frequently encountered in the emergency department of hospital. Twenty-one patients, who were suspected of BZD overdose, were treated with the antagonist of the central type BZD-receptors Ro 15-1788. Samples for toxicological analysis were taken before and after treatment. The patients were divided into three groups. In the first group (pure BZD overdose, n = 9), rapid and complete awakening was observed in all the patients (9/9) with 3.5 +/- 1.5 mg Ro 15-1788. In the second group of patients with multiple drugs poisoning (including BZD, n = 6), CNS depression improved in all the patients despite incomplete awakening. In the last group (n = 6), where no BZD were detected in toxicological samples, none of the comatous patients improved significantly during Ro 15-1788 administration, except one patient with pure ethanol intoxication. No undesirable effects are reported, except mild transitory withdrawal syndrome in three cases following rapid injection. This study supports the introduction of Ro 15-1788 as a useful antidote in the diagnosis and the treatment of drug-induced coma.

Lack of effect of nitrendipine on the pharmacokinetics and pharmacodynamics of midazolam during steady state

1. The possible interaction (as indicated by rat experiments) between calcium channel blocking agents and benzodiazepines has been evaluated in nine healthy subjects. 2. Subsequently to an intravenous loading dose (0.07 mg kg-1) midazolam was infused for 6 h (0.035 mg kg-1 h-1) and steady state plasma levels between 54 to 114 micrograms l-1 were achieved. Two hours after the bolus of midazolam a solution of 20 mg nitrendipine or placebo was administered in a randomized, double-blind crossover fashion. 3. The marked sedative-hypnotic effects of midazolam as assessed by visual analogue scales (about four fold increase in the sedation index) and choice reaction time (100% prolongation) indicated some form of adaptation or tolerance towards the end of the infusion. However, the midazolam-induced impairments were not affected by nitrendipine. 4. EEG-data indicated stabile benzodiazepine-like effects during the complete infusion period of midazolam (e.g. decrease in alpha activity, increase in sigma, delta 2 and beta 1 activity). Again, these alterations were not modified by nitrendipine. 5. There was also no pharmacokinetic interaction between both agents, since elimination of midazolam (t 1/2 = 2.5 +/- 0.8 h; CL = 548 +/- 143 ml min-1) was in close agreement with control values (t 1/2 = 2.4 +/- 0.6 h; CL = 512 +/- 102 ml min-1). Likewise, plasma levels of nitrendipine were comparable to literature data. 6. Thus, it could be concluded that nitrendipine does not affect the action of midazolam and therefore a direct involvement of calcium at the benzodiazepine receptor site is unlikely under our clinical conditions.

Pharmacokinetics and clinical use of flumazenil (Ro 15-1788)

Flumazenil (Ro 15-1788) is a specific benzodiazepine antagonist which can prevent or abolish selectively at the receptor level all centrally mediated effects of benzodiazepines. Following oral administration flumazenil is rapidly absorbed (peak concentrations are achieved after 20 to 90 minutes), but bioavailability is low (16%) due to significant presystemic elimination. As less than 0.2% of an intravenous dose was recovered as unchanged drug in the urine, extensive metabolism must occur and so far 3 metabolites of flumazenil (N-demethylated and/or hydrolysed products) have been identified. For the clinical value of flumazenil a rapid onset of action is mandatory, which is facilitated by its fast uptake and regional brain distribution as verified by positron emission tomography. The limited duration of benzodiazepine-antagonistic action of flumazenil (2 to 3 hours) is due to its rapid hepatic elimination. This can be characterised either by the short half-life (0.7 to 1.3 hours) or better by the high plasma or blood clearance of 520 to 1300 ml/min (31 to 78 L/h). The low plasma protein binding of flumazenil (about 40%) will not limit its wide distribution (apparent distribution volume 0.6 to 1.6 L/kg) or its partly flow-dependent hepatic elimination. Whereas in first trials flumazenil appeared to be without its own pharmacological effects, there is now increasing evidence that flumazenil is not devoid of intrinsic actions. Dependent on the dose, the basal clinical conditions and experimental tests, flumazenil has both weak agonist-like and inverse agonist-like properties which might be explained by a modulation of GABA-ergic activity. In several clinical studies intravenous doses down to 0.2mg of flumazenil initiated a rapid and reliable reversal of benzodiazepine-induced sedation, hypnosis or coma. Small incremental intravenous doses of 0.1 to 0.2mg of flumazenil are useful in benzodiazepine intoxications, in differential diagnosis of coma, excessive postoperative sedation and possibly in reversing paradoxical reactions of benzodiazepines. Because flumazenil is short acting, careful clinical observation is crucial. To maintain its antagonistic action repeated administrations will be necessary. At present, the therapeutic indications are restricted to some special situations. However, flumazenil is an interesting agent, which might contribute also to a better understanding and future development of more specific benzodiazepines, hopefully without the potential for dependence seen with existing compounds.

Flumazenil in benzodiazepine antagonism. Actions and clinical use in intoxications and anaesthesiology

In anaesthesia and in the intensive care unit, benzodiazepines have proven safe and effective agents for the induction and maintenance of sedation for a variety of therapeutic goals. However, in these contexts, or in benzodiazepine overdose, it is often desirable to be able to terminate or interrupt sedation without waiting for the effect of the benzodiazepine to become dissipated by normal metabolism and excretion. Flumazenil, a 1,4-imidazobenzodiazepine, is a highly effective, specific benzodiazepine antagonist which is indicated for use when the effect of a benzodiazepine must be attenuated or terminated at short notice. It acts by displacing other benzodiazepines from the receptor site by competitive inhibition. The onset of effect after intravenous administration occurs within 1 to 3 minutes. The optimal dosage is determined for each patient by a dose titration procedure and lies in the range 0.2 to 1.0mg in anaesthesiology, and 0.1 to 2.0mg in intensive care use. Despite its short elimination half-life of around 1 hour, after general anaesthesia or conscious to moderate sedation for short procedures, a single dose of flumazenil is usually sufficient to attain and maintain the desired level of consciousness. After intoxication with high benzodiazepine doses, the duration of effect of a single dose of flumazenil is not expected to exceed 1 hour. In such cases, the period of wakefulness can be prolonged as necessary by repeated low intravenous doses of flumazenil or by infusion (0.1 mg/hour). Flumazenil is well tolerated both systemically and locally. The only adverse events seen with greater frequency after flumazenil compared with placebo were nausea and/or vomiting after general anaesthesia, although the incidence of actual vomiting was not significantly different between the 2 groups. Since these effects were virtually absent in studies of intensive care patients and after sedation for short procedures, and were not seen in tolerability studies in healthy volunteers receiving intravenous bolus doses of up to 100mg, there may be a link between these symptoms and the other agents used in general anaesthesia, some of which have well-known emetic properties. Thus, flumazenil provides a safe and effective means of attenuating or reversing the CNS-depressant effects of benzodiazepines whenever indicated, e.g. following benzodiazepine-induced general anaesthesia, conscious sedation, or after benzodiazepine overdose, either alone or in combination with other agents.(ABSTRACT TRUNCATED AT 400 WORDS)

Does the benzodiazepine antagonist Ro 15-1788 antagonize the action of ethanol?

Ethanol aggravates benzodiazepine-induced central nervous depression by pharmacokinetic and/or pharmacodynamic interactions and Ro 15-1788 reverses promptly the hypnotic effects of benzodiazepines. We therefore studied the acute effects of Ro 15-1788 on the ethanol-induced sedation in six healthy male subjects. Subsequently to an oral loading dose (0.54 g ethanol kg-1) ethanol was infused for 4 h (0.15 g ethanol kg-1 h-1) and steady state blood levels between 0.9 to 1.2 g l-1 were reached within 2 h. At steady state and during the elimination phase of ethanol an intravenous bolus of 0.5 mg Ro 15-1788 or placebo was administered in a randomized, double-blind crossover fashion. The marked sedative effects of ethanol as assessed by visual analogue scales (2 to 6 fold increase in the sedation index), and choice reaction time (25 to 40% prolongation) were not affected by Ro 15-1788. However, the pharmaco-EEG indicated that Ro 15-1788 seems to reverse transiently the ethanol-induced changes in total alpha, delta, and slow alpha bands. There was no pharmacokinetic interaction between both agents since elimination of Ro 15-1788 (t1/2 = 1.2 +/- 0.7 h) and of ethanol (0.17 +/- 0.02 g l-1 h-1) were in good agreement with control values. Thus, it could be concluded that Ro 15-1788 might affect for a short while the action of ethanol by interfering with the benzodiazepine receptors.

Investigation of the actions of the benzodiazepine antagonists Ro 15-1788 and CGS 8216 using the schedule-controlled behavior of rats

Ro 15-1788 and CGS 8216 antagonise many of the pharmacological effects of benzodiazepines but both of these compounds have also been shown to exert behavioral effects when administered alone. In the present study the effects of Ro 15-1788 and CGS 8216, alone and in combination with diazepam and with the benzodiazepine receptor ligand zolpidem, were investigated. Diazepam and zolpidem produced dose-related decreases in rates of food-reinforced lever-pressing maintained by a fixed-ratio (FR 10) schedule. CGS 8216 also reduced response rates although Ro 15-1788, at several doses, produced small, but statistically significant, increases in responding. When the diazepam and zolpidem dose-response curves were re-established in the presence of a dose of Ro 15-1788 or CGS 8216 the depressant effects of the higher doses were antagonised. However, neither diazepam nor zolpidem blocked the rate reducing effect of CGS 8216 which may not therefore be due to an action at benzodiazepine receptors.