Reversal of the cerebral effects of diazepam in the dog by the benzodiazepine antagonist Ro15-1788

Positive and negative modulation of the GABA(A) receptor and outcome after traumatic brain injury in rats

Glutamate-mediated excitotoxicity has been shown to contribute to cellular dysfunction following traumatic brain injury (TBI). Increasing inhibitory function through stimulation of gamma-aminobutyric acid (GABA(A)) receptors may attenuate excitotoxic effects and improve outcome. The present experiment examined the effects of diazepam, a positive modulator at the GABA(A) receptor, on survival and cognitive performance in traumatically brain-injured animals. In experiment 1, 15 min prior to central fluid percussion brain injury, rats (n=8 per group) were injected (i.p.) with saline or diazepam (5 mg/kg or 10 mg/kg). Additional rats (n=8) were surgically prepared but not injured (sham-injury). Rats pre-treated with the 5 mg/kg dose of diazepam had significantly lower mortality (0%) than injured, saline-treated rats (53%). Also, diazepam-treated (5 mg/kg) rats had significantly shorter latencies to reach the goal platform in the Morris water maze test performed 11-15 days post-injury. In experiment 2, at 15 min post-injury, rats were given either saline (n=5) or 5 mg/kg diazepam (n=6). Rats treated with diazepam did not differ in mortality from injured rats treated with vehicle. However, rats treated with diazepam at 15 min post-injury had significantly shorter latencies to reach the goal platform in the Morris water maze than injured, vehicle-treated rats. In experiment 3, the post-injury administration of bicuculline (1.5 mg/kg, n=8), a GABA(A) antagonist, increased Morris water maze goal latencies compared to injured animals treated with saline (n=8). These results suggest that enhancing inhibitory function during the acute post-injury period produces beneficial effects on both survival and outcome following experimental TBI.

The effect of the benzodiazepine antagonist flumazenil on the sequels of diazepam given before upper gastrointestinal endoscopy. A double-blind randomized trial

The prolonged sedation of benzodiazepines may be inconvenient for the patient. Reversal of sedation, therefore, would be desirable. Accordingly, we assessed the efficacy of the benzodiazepine antagonist flumazenil in a placebo-controlled randomized trial including 40 adults undergoing upper gastrointestinal endoscopy under diazepam (Diazemuls) sedation. We found no significant differences between groups with regard to either performance (two tests) or duration (within 240 min) of sedation. There were no noticeable side effects.

Partial reversal of the cerebral effects of isoflurane in the dog by theophylline

The cerebral effects of adding theophylline to 1.4% isoflurane anaesthesia were studied in five dogs by a sagittal sinus outflow technique with direct measurement of the cerebral blood flow (CBF) and calculation of the cerebral metabolic rate for oxygen (CMRo2). Three 3 mg.kg-1 doses of theophylline were given with intervals of 10 min. Five min after the second and third dose, when the mean theophylline plasma concentration was 41 and 65 mumols.1(-1), respectively, CMRo2 had increased significantly with a mean value varying between 15% and 13%, and the EEG had changed from a sleep pattern to a more awake pattern in the four dogs with evaluable recordings. There were no significant changes in CBF or mean arterial blood pressure (MABP). It is concluded that the adenosine receptor antagonist theophylline in this study partially reversed the cerebral effects of isoflurane.

Midazolam and flumazenil in neuroanaesthesia

Of the numerous benzodiazepines currently available, only a few are used in anaesthetic practice. Midazolam is utilised as a premedicant, sedative, and an induction agent and produces minimal depression of ventilation or of the cardiovascular system. The anticonvulsant activity is similar to that of diazepam. In neuroanaesthesia midazolam may be an acceptable alternative to other intravenous induction agents like barbiturates or etomidate in patients with compromised intracranial compliance. Midazolam produces dose-related reductions in cerebral blood flow and cerebral oxygen consumption. However, midazolam does not necessarily prevent increases in intracranial pressure during induction of anaesthesia. In the electroencephalogram (EEG) midazolam produces a reduction in alpha-activity, an increase in theta-delta-activity and low-voltage beta-activity. Midazolam like other benzodiazepines does not affect early components of auditory and somatosensory evoked responses, whereas late cortical responses may be suppressed. Flumazenil, a specific benzodiazepine antagonist, has been demonstrated to be effective in reversing benzodiazepine-induced sedation. In the EEG midazolam-induced changes vanish almost instantaneously. Flumazenil is also effective in restoring the amplitudes of cortical auditory and somatosensory evoked responses. However, as has been demonstrated in head-injured patients and animal experiments after incomplete cerebral ischaemia, increases in cerebral blood flow and intracranial pressure cannot be excluded after flumazenil administration. When utilising flumazenil for wake-up procedures in midazolam-sedated patients with pathological intracranial compliance, flumazenil has to be titrated very carefully in low doses over prolonged periods.

Recovery from fixed-dose midazolam-induced anaesthesia and antagonism with flumazenil for outpatient arthroscopy

This study evaluated recovery after a fixed dose of midazolam as induction agent and the influence of flumazenil on recovery parameters in patients undergoing day-case surgery (arthroscopy of the knee). In 40 unpremedicated patients, anaesthesia was induced with midazolam 0.2 mg/kg, vecuronium bromide 0.1 mg/kg intravenously and 3 vol.% isoflurane in oxygen prior to intubation. Anaesthesia was maintained with nitrous oxide 66% in oxygen and 0.9 vol.% isoflurane. Ten minutes after the end of anaesthesia 20 patients received 0.2 mg flumazenil intravenously, followed by increments of 0.1 mg at 60 s intervals until eye opening. Recovery was assessed by the time to eye-opening, to answering five set questions correctly, and to recovering ocular balance (Maddox Wing test), and by comparing pre- and postoperative performance in a pencil and paper test (the p-deletion test). With the exception of ocular balance, all parameters showed a quicker improvement without side-effects in the flumazenil group. After 4 h all patients were fit for discharge. One month after the procedure, all patients were satisfied with the anaesthesia. Full recovery took on average 1.5 days (range between 0 h-10 days). Whilst the technique employing a fixed dose of midazolam as induction agent gives satisfactory intraoperative anaesthesia for day-case arthroscopy, further improvement can be made with the use of flumazenil which hastens recovery.

Reversal of flunitrazepam sedation with flumazenil. A randomized clinical trial

Fifty-nine male patients scheduled for transurethral resection of the prostate under flunitrazepam sedation and spinal analgesia were randomized in a double-blind trial to reversal of sedation with either the benzodiazepine antagonist flumazenil or placebo. Judged by degree of sedation, comprehension and cooperation as well as by estimation of orientation in time and space, flumazenil was superior to placebo (P less than 0.001). The median duration of anterograde amnesia was 16 min after flumazenil and 75 min after placebo (P less than 0.001). Adverse events were more frequent with placebo (P greater than 0.05), while no differences were evident with regard to laboratory data or cardiorespiratory function.

Partial reversal of the cerebral effects of isoflurane in the dog by the benzodiazepine antagonist flumazenil

Six dogs initially anaesthetized with isoflurane-N2O-O2 for surgery with cannulation of the sinus sagittalis for direct measurement of cerebral blood flow (CBF) and maintained with 1% isoflurane-N2-O2 anaesthesia, were given two 2-mg doses of the benzodiazepine antagonist flumazenil with an interval of 10 min. This was accompanied by a significant increase in the cerebral metabolic rate for oxygen (CMRO2) 10 min after the first 2-mg dose, and 5, 10 and 15 min after the second 2-mg dose, the increase varying in mean value from 9% to 14%. EEG was recorded in five of the six dogs and administration of flumazenil converted the EEG from a sleep pattern to an awake pattern in two of them. There were no significant changes in the CBF or mean arterial blood pressure (MABP) values. In the brain biopsies taken at the end of the study there were no significant changes in the adenylate energy charge (EC) and the lactate/pyruvate ratio (L/P) when compared to five other dogs not given flumazenil. It is concluded that flumazenil in this study demonstrated a partial antagonism of the cerebral effects of isoflurane.

Differential effects of Ro15-1788 in actions of chlordiazepoxide and ethanol

Three behavioral tests, namely, runway activity, horizontal dowel test and hypothermia, were used to compare the effects of Ro15-1788, a specific benzodiazepine antagonist, on the common neuropharmacological actions of chlordiazepoxide (CDP) and ethanol in C57BL/6J mice. Ro15-1788 completely reversed the CDP-induced inhibition of runway activity and incoordination on a horizontal dowel, but only partially antagonized the hypothermic effects of CDP. The latter phenomenon was likely to be due to the rapid elimination of Ro15-1788, but could also be due to the fact that hypothermia might not be a specific action of CDP. The sedative actions of ethanol were not antagonized at all by Ro15-1788. In fact, Ro15-1788 potentiated the incoordinating effect of ethanol as determined by the horizontal dowel test such that mice injected with Ro15-1788/ethanol had lower brain ethanol levels than mice injected with vehicle/ethanol when they fell off the dowel. In contrast, mice injected with Ro15-1788/CDP took longer to fall off and had significantly higher CDP levels at fall-off than mice injected with vehicle/CDP. The stimulatory effect of a low dose of ethanol on runway activity was reversed by Ro15-1788. These data are discussed in terms of the possible mechanisms of actions for CDP and ethanol.

Antagonism of diazepam-induced sedative effects by Ro15-1788 in patients after surgery under lumbar epidural block. A double-blind placebo-controlled investigation of efficacy and safety

The aim of this study was to assess the efficacy of Ro15-1788 and a placebo in reversing diazepam-induced effects after surgery under epidural block, and to evaluate the local tolerance and general safety of Ro15-1788. Fifty-seven patients were sedated with diazepam for surgery under epidural anaesthesia. Antagonism of diazepam-induced effects by Ro15-1788 was investigated postoperatively in a double-blind placebo-controlled trial. The patient's subjective assessment of mood rating, an objective test of performance, a test for amnesia, and vital signs were recorded for up to 300 min after administration of the trial drug. No significant differences between the two groups were observed for mood rating, amnesia, or vital signs. The Ro15-1788 group showed a significant improvement in the performance test up to 120 min after administration of the drug. There was no evidence of reaction at the injection site.