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PubMedDate not supplied

Treatment of benzodiazepine overdose with flumazenil. The Flumazenil in Benzodiazepine Intoxication Multicenter Study Group.

Flumazenil, a specific benzodiazepine antagonist, was evaluated as adjunctive therapy in the management of benzodiazepine overdose. Thirteen emergency departments enrolled 326 patients in this double-blind, placebo-controlled trial; 162 patients were randomly allocated to receive flumazenil (maximum dose, 30 ml, providing 3 mg of flumazenil), and 164 were allocated to receive placebo (maximum dose, 30 ml). A successful response was the attainment of a score of 1 or 2 on the Clinical Global Impression Scale (CGIS), denoting a very much improved or much improved status, 10 minutes after the start of intravenous administration of the test drug. Among those patients whose drug screen revealed the presence of benzodiazepines, 75 (77%) of 97 patients given flumazenil and 13 (16%) of 83 given placebo attained such a response. The mean CGIS score at 10 minutes for benzodiazepine-positive patients treated with flumazenil was 1.95 versus 3.58 for those given placebo. As determined by the Neurobehavioral Assessment Scale, 61% of patients who initially responded became resedated; in these patients, the effect of flumazenil lasted a median of 90 minutes. At the investigator's discretion, patients who did not achieve a criterion response in the double-blind trial could receive open-label flumazenil, titrated as in the double-blind phase. Among the benzodiazepine-positive patients, 9 (53%) of 17 patients from the flumazenil group responded to the additional flumazenil, and 58 (81%) of patients previously given placebo responded. Safety was assessed in all 326 patients given the test drug. The most frequent adverse experiences after the administration of flumazenil were agitation (7%), vomiting (7%), abnormal crying (4%), and nausea (4%); these effects were observed with a lower frequency in the placebo group. Serious adverse experiences were reported in 4 patients; these included seizures and cardiac arrhythmias. Of the 3 patients with seizures, 2 had ingested large doses of cyclic antidepressants in addition to the benzodiazepine. The toxicology screen for 1 of the 2 showed 1900 ng/ml of amoxapine and 900 ng/ml of nortriptyline; the toxicology screen for the other, who also had ventricular tachycardia, showed 1928 ng/ml of loxapine and 301 ng/ml of amoxapine. The results of this study confirm published reports of the efficacy of flumazenil in reversing benzodiazepine-induced sedation in patients with benzodiazepine overdose. This was accomplished irrespective of the presence of coingested drugs. Flumazenil is not recommended for patients with serious cyclic antidepressant poisoning or those who use benzodiazepines therapeutically to control seizure disorders. When used as recommended, however, flumazenil has been shown to have an acceptable safety level.

Adolescent↗
PubMed1997

Safety and efficacy of flumazenil in the reversal of benzodiazepine-induced conscious sedation. The Flumazenil Pediatric Study Group.

OBJECTIVE: To determine the safety and efficacy of flumazenil when given for reversal of benzodiazepine-induced conscious sedation in children. DESIGN: Multicenter study conducted in emergency departments and pediatric endoscopy, bronchoscopy, or oncology suites. PATIENTS: One hundred seven children (median age, 6 years; range, 1 to 17 years) who received intravenous benzodiazepine for an invasive procedure. INTERVENTIONS: Flumazenil was given in increments of 0.01 mg/kg (0.2 mg maximum) at 1-minute intervals to a maximum total dose of 0.05 mg/kg (1.0 mg maximum). MEASUREMENTS: Clinical efficacy was assessed by the Clinical Global Impression Scale and Observer's Assessment of Alertness/Sedation Scale. The OAA/S, vital signs, lead II electrocardiogram, and clinical assessments were recorded at 0, 10, 30, 60, 90, and 120 minutes after flumazenil was given. RESULTS: All children received midazolam (mean total dose, 0.18 mg/kg) for sedation. One hundred (96%) patients achieved a complete or partial response to flumazenil by 10 minutes after its administration, on the basis of their CGIS scores (the mean dose of flumazenil administered at the time of the first complete response was 0.017 +/- 0.010 mg/kg). Seventy-one of 93 (76%) patients with a baseline OAA/S score < or = 3 (1 = deep sleep, 5 = alert) experienced an increase of > or = 2 points at 10 minutes after flumazenil administration, and 81 of 93 (87%) had a score of 4 or 5 after flumazenil administration. Seven patients, all within the 1- to 5-year age range, experienced resedation after initially responding to flumazenil. Thirty-seven of 107 patients (35%) experienced a total of 56 adverse events, most of which were considered to be unrelated to flumazenil administration. The most frequently occurring adverse events were abnormal crying, dizziness, nausea, fever, and headache. There were no clinically significant changes in vital signs or ECG tracings. No adverse events resulted in premature termination of drug administration. CONCLUSIONS: Flumazenil promptly and effectively reverses the central nervous system depressant effects of midazolam in children undergoing conscious sedation, with no significant adverse effects. Because of the potential for resedation, children who receive flumazenil should be monitored for 1 to 2 hours after its administration.

Adolescent↗
PubMedDate not supplied

Reversal of central benzodiazepine effects by flumazenil after conscious sedation produced by intravenous diazepam. The Flumazenil in Intravenous Conscious Sedation with Diazepam Multicenter Study Group I.

Flumazenil is a competitive benzodiazepine antagonist that rapidly reverses the residual effects of benzodiazepines following intravenous conscious sedation. In a double-blind, multicenter study, postoperative patients who had been sedated with intravenous diazepam were randomly allocated to receive intravenous doses of flumazenil (0.4 mg to 1 mg) or placebo. Levels of sedation and psychomotor impairment were evaluated prestudy, at baseline, and at 6 intervals from 5 to 180 minutes posttreatment. A global evaluation of effectiveness was made at the 5-minute assessment, and memory was assessed at the 180-minute assessment. Flumazenil (mean dose: 0.73 mg [7.3 ml]) was significantly more effective than placebo (mean dose: 8.9 ml) in reversing sedation, psychomotor impairment, and amnesia within 5 minutes after the start of administration. At the 5-minute posttreatment assessment, 84% of 102 flumazenil-treated patients (compared with 42% of 52 placebo-treated patients) experienced complete reversal of sedation. Ninety-two percent of 93 flumazenil-treated patients (compared with 41% of 46 placebo-treated patients) had normal psychomotor function. Reversal of amnesia at the 5-minute assessment was achieved in 75% of 101 flumazenil-treated patients and in 20% of 51 placebo-treated patients. Statistically significant differences between flumazenil and placebo were also observed at the 15-minute assessment. Thereafter there were no significant differences between the two treatment groups. Most (70%) flumazenil-treated patients exhibited no recurrence of sedation during the 180-minute assessment period. The most frequent adverse reaction in the flumazenil group was dizziness (6%). There were no serious adverse experiences related to the test drug. Flumazenil provided prompt, controlled reversal of residual effects, especially sedation, in the majority (84%) of patients recovering from intravenous conscious sedation induced by diazepam. For most (70%) of these flumazenil-treated patients, the reversal was maintained throughout the 180-minute assessment.

Adolescent↗
PubMedDate not supplied

Reversal of central nervous system effects by flumazenil after intravenous conscious sedation with midazolam: report of a multicenter clinical study. The Flumazenil in Intravenous Conscious Sedation with Midazolam Multicenter Study Group I.

Flumazenil, a benzodiazepine antagonist, reverses the residual central nervous system effects of benzodiazepines. In this US double-blind, multicenter study, the efficacy of flumazenil was compared with that of placebo in antagonizing the effects of midazolam, a benzodiazepine used to induce intravenous conscious sedation. The mean dose of flumazenil was 0.7 mg, administered intravenously. At 5 minutes posttreatment, 82% of 131 flumazenil-treated patients, compared with 15% of 65 placebo-treated patients, demonstrated complete reversal of sedation. In 85% of patients who responded to flumazenil, this reversal of sedation was maintained throughout the 180-minute observation period. Psychomotor performance returned to prestudy levels 5 minutes posttreatment in 87% of the flumazenil-treated patients, compared with 28% of the placebo-treated patients. At the doses administered, flumazenil was less effective in reversing midazolam-induced amnesia, with only 60% of patients demonstrating partial recovery of memory. It was, nevertheless, more effective than placebo. Flumazenil was well tolerated. Dizziness (10%) and nausea (9%) were the most frequently reported adverse effects. Results of this study demonstrate that flumazenil antagonizes the central nervous system effects of midazolam after intravenous conscious sedation.

Adolescent↗
PubMedDate not supplied

Reversal of central benzodiazepine effects by flumazenil after intravenous conscious sedation with diazepam and opioids: report of a double-blind multicenter study. The Flumazenil in Intravenous Conscious Sedation with Diazepam Multicenter Study Group II.

The efficacy and safety of a new benzodiazepine antagonist, flumazenil, were assessed in a double-blind multicenter study. Flumazenil (mean dose, 0.76 mg) or placebo (mean dose, 8.9 ml) was administered intravenously to 130 and 67 patients, respectively, who had been given diazepam in conjunction with an opioid (fentanyl, meperidine, or morphine) for the induction and maintenance of intravenous conscious sedation for diagnostic or therapeutic surgical procedures. The group assessable for efficacy comprised 122 patients treated with flumazenil and 64 patients given placebo. After 5 minutes, 80/115 (70%) flumazenil-treated patients, compared with 21/63 (33%) placebo-treated patients, were completely awake and alert, as indicated by a score of 5 on the Observer's Assessment of Alertness/Sedation Scale. Ninety-five percent of patients in each group who attained a score of 5 at the 5-minute assessment showed no loss of alertness throughout the 180-minute assessment period. Flumazenil-treated patients also performed significantly better on the Finger-to-Nose Test and the recall of pictures shown at the 5-minute assessment. Flumazenil was well tolerated, with no serious adverse effects reported. Thirty-nine (30%) of flumazenil-treated patients, compared with 17 (25%) of placebo-treated patients had one or more drug-related adverse experiences. The most common adverse effects were nausea and vomiting in the flumazenil group and nausea and injection-site pain in the placebo group. Flumazenil was found to promptly reverse sedation induced by diazepam in the presence of opioids.

Adolescent↗
PubMedDate not supplied

Reversal of the central effects of midazolam by intravenous flumazenil after general anesthesia in outpatients premedicated with an opioid and a muscle relaxant: report of a multicenter double-blind clinical study. The Flumazenil in General Anesthesia in Outpatients Study Group II.

Flumazenil was studied in a double-blind multicenter trial to confirm its efficacy and safety in antagonizing the central effects of benzodiazepines after general anesthesia (midazolam, short-acting narcotic, nitrous oxide) with muscle relaxants and selected potent volatile anesthetics as needed. One hundred seventy-two outpatients were randomly assigned to receive either flumazenil or placebo titrated to the point of reversal of sedation or a maximum dose of 1 mg of flumazenil or 10 ml of placebo. The test drug was given intravenously (0.2 mg flumazenil or 2 ml placebo) at 1-minute intervals. Tests of alertness, psychomotor function, and memory were conducted prestudy and at baseline before the administration of flumazenil and at 5-, 15-, 30-, 60-, 120-, and 180-minute intervals after administration. The changes from prestudy or baseline scores were analyzed to compare differences between treatment groups. Seventy-five percent of the 105 flumazenil-treated patients and 14% of the 55 placebo-treated patients who met the qualifications for efficacy evaluations obtained a criterion level of response as measured by the Observer's Assessment of Alertness/Sedation Scale. Most (76%) patients who were alert at 5 minutes maintained their level of wakefulness throughout the 180-minute observation period. All 172 patients were included in evaluations of safety. Fifty percent of 113 flumazenil-treated patients and 31% of 59 placebo-treated patients reported one or more adverse experiences. The most frequently reported were nausea, vomiting, and dizziness. Only 6 adverse effects in the flumazenil group and 1 in the placebo group were considered severe; the remainder were mild or moderate. None were considered serious or potentially serious. Postoperative administration of flumazenil (mean dose, 0.85 mg) safely provided a prompt, controlled reversal of the sedative and psychomotor effects of midazolam in most patients.

Adult↗
PubMedDate not supplied

Reversal of the central effects of midazolam by intravenous flumazenil after general anesthesia in outpatients: a multicenter double-blind clinical study. The Flumazenil in General Anesthesia in Outpatients Study Group I.

In a US double-blind, multicenter study, flumazenil, a benzodiazepine antagonist, administered postoperatively in a mean intravenous dose of 0.67 mg (range, 0.2 to 1 mg), was superior to placebo in reversing sedation and other central nervous system effects of benzodiazepines in outpatients recovering from general anesthesia induced by midazolam, fentanyl or sufentanil, and nitrous oxide. Within 5 minutes after administration of flumazenil, sedation was reversed in 94% (87 of 93) of flumazenil-treated patients, compared with 13% (6 of 46) of placebo-treated patients. The criterion response (Observer's Assessment of Alertness/Sedation Scale score of 4 or 5) that was achieved at 5 minutes was maintained in 79 (93%) of 85 patients throughout the 180-minute observation period. Psychomotor performance, measured by the Finger-to-Nose Test, was rated as normal at 5 minutes posttreatment for 77% (71 of 92) of flumazenil-treated patients, and 4% (2 of 46) of placebo-treated patients. The reversal of amnesia, as determined by the Picture Recall Test was less consistent. Patients given flumazenil did not experience more pain at the operative site or require more analgesic medication than did those given placebo. Nausea (flumazenil 24%; placebo 15%), dizziness (flumazenil 12%; placebo 2%), and vomiting (flumazenil 10%; placebo 9%) were the most frequent adverse effects in each group. In conclusion, flumazenil provided prompt arousal from benzodiazepine-induced sedation and was well tolerated.

Adolescent↗
PubMed2006

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

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

Animals↗
PubMedDate not supplied

Reversal of central benzodiazepine effects by intravenous flumazenil after conscious sedation with midazolam and opioids: a multicenter clinical study. The Flumazenil in Intravenous Conscious Sedation with Midazolam Multicenter Study Group II.

The efficacy and safety of flumazenil in antagonizing the central effects of the benzodiazepine midazolam was demonstrated in patients in whom conscious sedation was induced with midazolam plus an opioid (fentanyl, meperidine, or morphine). In a double-blind, multicenter study, 240 patients were administered flumazenil postoperatively at an average intravenous dose of 0.7 mg (7 ml) and 114 patients were administered an average dose of 9 ml placebo. Complete reversal of sedation was observed in 80% of flumazenil-treated patients and 30% of placebo-treated patients 5 minutes posttreatment. In 87% of patients who responded to flumazenil, the level of alertness was maintained throughout the 180-minute observation period. Midazolam-impaired psychomotor performance returned to normal 5 minutes posttreatment in 80% of the flumazenil-treated patients and 28% of the placebo-treated patients. Flumazenil was less effective in reversing midazolam-induced amnesia, with only 70% of flumazenil-treated patients (and 15% of placebo-treated patients) able to recall the picture shown them at the 5-minute assessment, and fewer patients able to recall pictures shown at later times. Flumazenil was well tolerated, although adverse effects were reported slightly more often than in the placebo group. The most frequent adverse events in both groups were dizziness and nausea. Vital signs were not affected.

Adolescent↗
PubMedDate not supplied

Reversal of the central effects of midazolam by intravenous flumazenil after general anesthesia and use of a long-acting opioid in hospitalized patients: report of a multicenter double-blind clinical study. The Flumazenil in General Anesthesia in Hospitalized Patients Study Group II.

A double-blind clinical trial was conducted to evaluate the efficacy and safety of flumazenil, a benzodiazepine antagonist, in 146 hospitalized patients, who had had general anesthesia induced by midazolam and a long-acting opioid. Ninety-eight patients received flumazenil and 48 received placebo. Administered postoperatively at a mean intravenous dose of 0.84 mg (range: 0.2 mg to 1 mg), flumazenil reversed benzodiazepine-induced sedation to a greater extent than did placebo. At 5 minutes posttreatment, 61 (76%) of 80 flumazenil-treated patients and 7 (18%) of 40 placebo-treated patients had attained a score of 4 or 5 on the Observer's Assessment of Alertness/Sedation Scale, indicating that they were drowsy or fully awake and alert. This level of arousal was maintained for the full 180-minute posttreatment assessment period in 79% of flumazenil-treated patients. Between-group differences in mean change from baseline in level of alertness were statistically significant (P < 0.01) until 60 minutes posttreatment, when the spontaneous recovery of placebo-treated patients resulted in declining intergroup differences. The global efficacy rating (based on the physician's general impression of the effectiveness of the reversal of sedation 5 minutes after test drug administration) was good or excellent in 64 (80%) of the 80 flumazenil-treated patients and 5 (13%) of the 40 placebo-treated patients evaluated. Flumazenil, compared with placebo, was not associated with an increased frequency of operative-site pain, and no serious adverse effects of this benzodiazepine antagonist were reported. The most frequent adverse experiences in both treatment groups were nausea, shivering, and operative-site pain. Vomiting, dizziness, and injection-site reactions were also reported in > or = 5% of patients treated with flumazenil.

Adult↗
PubMedDate not supplied

Effect of intravenous flumazenil on reversal of the central effects of midazolam used with short-acting opioids for general anesthesia in hospitalized patients: report of a multicenter, double-blind clinical study. The Flumazenil in General Anesthesia in Hospitalized Patients Study Group I.

Midazolam, a short-acting benzodiazepine central nervous system (CNS) depressant widely used for the induction and maintenance of general anesthesia, is often supplemented with short-acting opioids for general anesthesia. Administered postoperatively, flumazenil, a specific benzodiazepine antagonist, reverses the CNS sedative effects of midazolam. In a double-blind clinical trial in hospitalized patients, flumazenil, administered postoperatively at an average intravenous dose of 0.89 mg (range: 0.4 mg to 1 mg), was more effective than placebo in reversing sedation and other residual effects of benzodiazepines in patients recovering from general anesthesia induced by midazolam (mean dose 29 mg) in conjunction with fentanyl (mean dose 0.4 mg) or sufentanil (mean dose 0.056 mg). Five minutes posttreatment, 87 (83%) of 124 flumazenil-treated patients and 6 (10%) of 60 placebo-treated patients had attained the criterion response for reversal of sedation. Of these patients, 60% in the flumazenil group, compared with 100% in the placebo group, retained their degree of alertness throughout the 3-hour observation period. Between-group differences were significant until 60 minutes posttreatment, when the effect of the benzodiazepines had spontaneously waned in the placebo group. The Physician's Global Efficacy Rating, providing an overall measure of efficacy 5 minutes after test drug administration, was good or excellent for 86% of the flumazenil-treated patients, as compared with 7% of the placebo-treated patients evaluated. Measurements of psychomotor function and memory also showed significant between-group differences. Flumazenil, compared with placebo, was not associated with a substantially greater frequency of operative-site pain. These results demonstrate that the efficacy and safety of flumazenil were not compromised by the addition of a short-acting opioid to the anesthetic regimen.

Adolescent↗
PubMed1998

In vivo [11C]flumazenil-PET correlates with ex vivo [3H]flumazenil autoradiography in hippocampal sclerosis.

By using [11C]flumazenil-positron emission tomography ([11C]FMZ-PET), we have previously shown that reductions of central benzodiazepine receptors (cBZRs) are restricted to the hippocampus in mesial temporal lobe epilepsy (mTLE) caused by unilateral hippocampal sclerosis (HS). Receptor autoradiographic studies on resected hippocampal specimens from the same patients demonstrated loss of cBZRs that was over and above loss of neurons in the CA1 subregion. Here, we report the first direct comparison of in vivo cBZR binding with [11C]FMZ-PET and ex vivo binding using [3H]FMZ autoradiography. We applied a magnetic resonance imaging-based method for partial volume effect correction to the PET images of [11C]FMZ volume of distribution ([11C]FMZ Vd) obtained in 10 patients with refractory mTLE due to unilateral, histologically verified HS. Saturation autoradiography was performed on the hippocampal specimens obtained from the same patients, allowing calculation of receptor availability ([3H]FMZ Bmax). After correction for partial volume effect, [11C]FMZ Vd in the body of the epileptogenic hippocampus was reduced by a mean of 42.1% compared with normal controls. [3H]FMZ Bmax, determined autoradiographically from the same hippocampal tissue, was reduced by a mean of 42.7% compared with control hippocampi. Absolute in vivo and ex vivo measurements of cBZR binding for the body of the hippocampus were significantly correlated in each individual. Our study demonstrates that reduction of available cBZR on remaining neurons in HS can be reliably detected in vivo by using [11C]FMZ-PET after correction for partial volume effect.

Adult↗
PubMedDate not supplied

Isolation and pharmacological characterization of microsomal human liver flumazenil carboxylesterase.

PURPOSE: In vivo the biotransformation of the imidazobenzodiazepine antagonist flumazenil leads to the formation of two metabolites, flumazenil acid and N-demethylated flumazenil. In the present study we investigated the role of carboxylesterases for the metabolism of flumazenil. METHODS: We purified a non-specific carboxylesterase (EC 3.1.1.1) from human liver microsomes that catalyzes the hydrolysis of flumazenil to flumazenil acid and, in presence of methanol the formation of flumazenil methyl ester an in vivo unknown metabolite. The purification procedure included solubilization of the microsomes obtained from human livers with Triton X-100 and subsequent chromatography of the 100,000 x g supernatant on blue-sepharose, DEAE-sepharose, hydroxyapatite and final chromatofocusing. RESULTS: The purified esterase isozyme exhibited an apparent subunit molecular weight of 59 kDa as estimated by SDS gelelectrophoresis, a native molecular weight of 170 kDa determined by a calibrated gel filtration column suggesting that the active enzyme is a trimer. The isoelectric point of the enzyme was approximately 5.4. The specific activities of the purified enzyme were 5.8 nmol/(min*mg protein) protein for the formation of flumazenil acid and 31 nmol/(min*mg protein) for the synthesis of the flumazenil methylester. The purified enzyme obeys simple Michaelis-Menten kinetics with K(M) values of 665 microM for flumazenil acid, 1011 mM for methanol and 900 microM for the flumazenil methylester. PMSF, a specific inhibitor for serine proteases and mammalian acetylcholinesterase, completely inhibited the formation of flumazenil -acid and the flumazenil methylester at a concentration of 100 microM. No synthesis of the flumazenil -methylester could be observed by incubation of the purified esterase with flumazenil acid in the presence of methanol leading to the conclusion that the enzymatically catalyzed reaction is a transesterification. The purified esterase was digested with endoproteinase LysC. A 15 amino acid long peptide was isolated and showed identical matches to carboxylesterase cDNAs from human liver and lung. CONCLUSION: Our results show that carboxylesterase isozymes play an important role in the detoxification and metabolism of flumazenil. Because of enzymatic, catalytic and structural properties a similarity of the characterized flumazenil carboxylesterase with human liver cocaine carboxylesterase is possible.

Animals↗
PubMed1999

Discriminative stimulus effects of flumazenil in untreated and in diazepam-treated rhesus monkeys.

RATIONALE: Long-term use of benzodiazepine agonists can have adverse effects (e.g., development of dependence), thereby limiting their clinical usefulness. OBJECTIVES: The goal of the current study was to examine the discriminative stimulus effects of flumazenil in untreated and diazepam-treated monkeys to determine whether this type of procedure could be used to examine benzodiazepine dependence. METHODS: Flumazenil (0.32 mg/kg s.c.) was established as a discriminative stimulus in eight monkeys receiving 5.6 mg/kg/day of diazepam (p.o.); four responded under a fixed ratio (FR)5 schedule of stimulus-shock termination (SST) and four responded under a FR5 schedule of food presentation. For comparison, 1.0 mg/kg flumazenil (s.c.) was established as a discriminative stimulus in four untreated monkeys responding under a FR5 schedule of SST. RESULTS: Flumazenil dose-dependently increased responding on the flumazenil-appropriate lever in all monkeys. In diazepam-treated monkeys, Ro 15-4513, ethyl beta-carboline-3-carboxylate and bretazenil substituted for flumazenil with pentylenetetrazole substituting in some monkeys; other drugs failed to substitute for flumazenil. Acute administration of 10.0 mg/kg diazepam (s.c.) shifted the flumazenil dose-effect curve threefold to the right of the control dose-effect curve. Temporary suspension of diazepam treatment produced a time-related increase in flumazenil-lever responding that was reversed by diazepam. In untreated monkeys, midazolam substituted for flumazenil, with other drugs, including those with primary mechanisms of action at non-gamma-aminobutyric acid(A) receptors, substituting in some monkeys. Ro 15-4513 did not substitute in any untreated monkey. CONCLUSIONS: The flumazenil discriminative stimulus appears to be pharmacologically selective in treated monkeys with only negative and low efficacy positive modulators substituting for flumazenil; in contrast, a variety of drugs substitute for flumazenil in untreated monkeys. This apparent difference in selectivity suggests that diazepam treatment modifies the flumazenil discriminative stimulus perhaps due to the development of dependence.

Animals↗
PubMed1990

Clinical experience with the benzodiazepine antagonist flumazenil in suspected benzodiazepine or ethanol poisoning.

The clinical efficacy of different doses of the specific benzodiazepine antagonist flumazenil was studied in a total of 72 patients with benzodiazepine or ethanol overdose. In a randomized double-blind study, 18 patients (group 1) and eight patients (group 2) with suspected benzodiazepine overdose received 5 mg (group 1) or 1 mg (group 2) flumazenil or placebo, respectively. The stage of coma, heart rate, blood pressure and respiratory rate were monitored within the following 15 min. If no change in the stage of coma was observed, 5 mg (group 1) or 1 mg (group 2) flumazenil were given, and the stage of coma, heart rate and blood pressure were again monitored. In a similar way, the effect of 5 and 1 mg flumazenil was investigated in 13 patients (group 3) and four patients (group 4) with ethanol intoxication. In an open trial, the clinical efficacy of flumazenil for the diagnosis of benzodiazepine or ethanol overdose was studied in 29 patients (group 5). In all patients, a toxicological screening confirmed benzodiazepine or ethanol overdose. None of the patients receiving placebo showed effects on stage of coma, heart rate, blood pressure or respiratory rate. Patients with benzodiazepine overdose who received 5 mg flumazenil regained consciousness about 1-2 min after the end of injection. The effect of 1 mg flumazenil (group 2) on benzodiazepine-induced coma was less pronounced. In patients with ethanol overdose (group 3), ethanol-induced coma was reversed after 5 mg flumazenil more slowly than in patients of group 1. No effect of flumazenil on ethanol-induced coma was observed in group 4. In group 5, flumazenil proved to be useful for diagnosing benzodiazepine or ethanol intoxication. In one patient with coma due to carbamazepine overdose, flumazenil was also found to be effective. Additionally, a possible analytical interference of flumazenil and its metabolites with the identification of other benzodiazepines by a toxicological screening procedure was studied. Even after an oral dose of 200 mg flumazenil, no interference with immunological benzodiazepine assays (EMIT, TDX, and RIA) was found. A metabolite and an artifact of flumazenil could be identified in urine by gas chromatography/mass spectrometry.

Adolescent↗
PubMed1996

Use of flumazenil in the treatment of drug overdose: a double-blind and open clinical study in 110 patients.

OBJECTIVES: To assess the efficacy, usefulness, safety, and dosages of flumazenil required when flumazenil is used in the diagnosis of benzodiazepine-induced coma (vs. other drug-induced coma), and to reverse or prevent the recurrence of unconsciousness. DESIGN: A two-phase study: a controlled, randomized, double-blind study followed by a prospective, open study. SETTING: An 800-bed, teaching, university-affiliated hospital. PATIENTS: Unconscious patients (n = 110) suspected of benzodiazepine overdose, graded 2 to 4 on the Matthew and Lawson coma scale, were treated with flumazenil, the specific benzodiazepine receptor antagonist. The first 31 patients were studied in a double-blind fashion, while the rest of the patients were given flumazenil according to an open protocol. INTERVENTIONS; All patients received supplemental oxygen; endotracheal intubation was performed, and synchronized intermittent mandatory ventilation was initiated whenever it was deemed necessary. A peripheral intravenous cannula was inserted, as were indwelling arterial and urinary bladder catheters. Blood pressure, electrocardiogram, respiratory rate, end-tidal CO2, and core temperature were continuously monitored. The first 31 double-blind patients received either intravenous flumazenil (to a maximum of 1 mg) or saline, while the rest of the patients were given flumazenil until either regaining consciousness or a maximum of 2.5 mg was injected. Patients remaining unconscious among double-blind patients or those patients relapsing into coma after the first dose were later treated in the open phase of the study. Treatment continued by boluses or infusion as long as efficacious. MEASUREMENTS AND MAIN RESULTS: Fourteen of 17 double-blind, flumazenil-treated patients woke after a mean of 0.8 +/- 0.3 (SD) mg vs. one of 14 placebo patients (p < .001). Seventy-five percent of the aggregated controlled and uncontrolled patients awoke from coma scores of 3.1 +/- 0.6 to 0.4 +/- 0.5 (p < .01) after the injection of 0.7 +/- 0.3 mg of flumazenil. These patients had high benzodiazepine serum blood concentrations. Twenty-five percent of the patients did not regain consciousness. These patients had very high serum concentrations of nonbenzodiazepine drugs. Sixty percent of the responders who had primarily ingested benzodiazepines remained awake for 72 +/- 37 mins after flumazenil administration; 40% relapsed into coma after 18 +/- 7 mins and various central nervous system depressant drugs were detected in their blood in addition to benzodiazepines. Seventy-one percent of the patients had ingested tricyclic antidepressants. Seventy-eight percent of the responders were continually and efficaciously treated for < or = 8 days. Fourteen (25%) of the intubated patients were extubated safely while 12 patients, who had shown increased respiratory insufficiency, resumed satisfactory respiration after flumazenil injection. Five cases of transient increase in blood pressure and heart rate were encountered. There were 27 mildly unpleasant "waking" episodes, such as anxiety, restlessness, and aggression, but no patient had benzodiazepine withdrawal signs, convulsions, or dysrhythmia, most noticeably absent in tricyclic antidepressant-intoxicated patients. CONCLUSIONS: Flumazenil is a valid diagnostic tool for distinguishing pure benzodiazepine from mixed-drug intoxication or nondrug-induced coma. Flumazenil is effective in preventing recurrence of benzodiazepine-induced coma. Respiratory insufficiency is reversed after its administration. Flumazenil is safe when administered cautiously, even in patients with coma caused by a mixed overdose of benzodiazepine plus tricyclic antidepressants.

Adult↗
PubMed1988

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.

Anesthesia↗
PubMed1999

Flumazenil discrimination by humans under a two-response and a novel-response procedure.

In this study we assessed the discriminative stimulus, self-reported, and performance effects of flumazenil in humans. The first group (n = 6) was trained to discriminate flumazenil (0.56 mg/70 kg i.v.) from saline and tested with flumazenil (0.10, 0.32, 0.56, and 1.0 mg/70 kg) under a two-response drug discrimination procedure. The second group (n = 8) was trained to discriminate flumazenil (0.56 mg/70 kg i.v.) from saline and tested with flumazenil (0.32, 0.56, and 1.0 mg/70 kg), midazolam (0.10, 0.56, and 1.0 mg/70 kg), and caffeine (75 mg/70 kg) under a novel-response drug discrimination procedure. In both groups, flumazenil was acquired and maintained as a discriminative stimulus. Flumazenil dose-dependently increased flumazenil-appropriate responding and ratings of strength of drug effect and sedation, and decreased ratings of stimulant effects and psychomotor performance. Under the novel-response procedure, midazolam produced dose-dependent increases in flumazenil-appropriate responding. However, midazolam produced 43 and 25% novel responding at the intermediate and highest test doses, respectively. Midazolam dose-dependently increased ratings of strength of drug effect and sedation, and decreased ratings of stimulant effects and psychomotor performance. The magnitude of effects on ratings of strength of drug effect and sedation were comparable after flumazenil and midazolam, but psychomotor performance effects were greater after midazolam than after flumazenil. Caffeine produced mostly saline-appropriate responding. The results indicate that flumazenil has agonist effects similar to those of midazolam; however, novel responding after midazolam, and the greater performance decrement after midazolam, suggest that flumazenil does not act as a traditional benzodiazepine agonist.

Adolescent↗