High-dose flumazenil potentiates the hypnotic activity of propofol, but not that of thiopental, in ddY mice

Administration of lipid emulsion reduced the hypnotic potency of propofol more than that of thiamylal in mice

Administration in a lipid emulsion can modify the pharmacodynamics of drugs via a process known as lipid resuscitation. However, the detailed mechanism remains unclear. We studied the volume and another pharmacodynamic effect, the lipid sink, using propofol and thiamylal. Male adult mice (ddY) were intravenously administered 10 ml/kg propofol or thiamylal diluted with physiological saline, 10% soybean oil, or 20% soybean oil. The 50% effective dose (ED50) for achieving hypnosis was calculated using probit analysis. To investigate the volume effect, 0, 10, or 20 ml/kg of saline or soybean oil was administered, either simultaneously or beforehand. Next, a two- or three-fold dose of the anesthetics was administered and the durations of anesthesia were measured. Finally, at 30 s after the first injection, supplemental soybean oil was administered. The mean (± SE) ED50 values of propofol and thiamylal were 5.79 mg/kg (0.61) and 8.83 mg/kg (0.84), respectively. Lipid dilution increased the ED50 values of both anesthetics. After injection of a dose two-fold the ED50 value, the respective mean (± SD) durations of anesthesia were 125 ± 35 s and 102 ± 38 s. Supplemental administration of soybean oil significantly shortened the duration of anesthesia of propofol, but not that of thiamylal. The results indicate that administration of a lipid emulsion vitiated the anesthetic effect of propofol by reducing the non-emulsified free fraction in the aqueous phase, which may elucidate the lipid resuscitation likely caused by the lipid sink mechanism.

Effect of Flumazenil on Emergence Agitation after Orthognathic Surgery: A Randomized Controlled Trial

Flumazenil, a gamma-aminobutyric acid receptor antagonist, can promote arousal even under general anesthesia without the use of benzodiazepines. We hypothesized that flumazenil could promote arousal and reduce emergence agitation in patients undergoing orthognathic surgery with sevoflurane anesthesia. One hundred and two patients were randomly allocated to the control or flumazenil group. Saline or flumazenil was administered at the end of the surgery. The incidence of emergence agitation was measured by using Aono’s four-point scale, with scores of 3 and 4 indicating emergence agitation. The primary outcome was the incidence of emergence agitation. Secondary outcomes included duration of emergence agitation and time intervals between the discontinuation of anesthetics, first response, extubation, and post-anesthesia care-unit discharge readiness. The incidence of emergence agitation was 58.3% and 38.9% in the control and flumazenil groups, respectively, but it was not statistically significant. However, the duration of emergence agitation was shorter in the flumazenil group (p = 0.012). There were no significant differences in the time intervals between the discontinuation of anesthetics, first response, and extubation. Although flumazenil did not reduce the incidence of emergence agitation in patients undergoing orthognathic surgery with sevoflurane anesthesia, it can be considered as an option for awakening patients in terms of improving emergence profiles.

JM-1232(-) and propofol, a new combination of hypnotics with short-acting and non-cumulative preferable properties

Drug interactions are significant in anesthesiology because drug combinations can potentially possess novel properties. The pharmacological advantages of a new combination of the benzodiazepine receptor agonist JM-1232(-) and propofol were investigated in mice. Male adult mice were administered JM-1232(-) or propofol or combinations of the two drugs intravenously. Loss of the righting reflex was evaluated as achieving hypnosis, and the time until recovery of the reflex was measured as hypnosis time. After determining the ED50, doses double and triple the ED50 of propofol were injected with JM-1232(-) to compare hypnosis time. The injections were repeated four times, and the hypnosis times were compared. Flumazenil was administered separately immediately after the last dose was injected. The ED50 values ([95% confidence interval]) for hypnosis were 3.76 [3.36-4.10] for JM-1232(-) and 9.88 [8.03-11.58] mg kg-1 for propofol. Co-administration of 0.5 and 1 mg kg-1 JM-1232(-) reduced the ED50 values of propofol to 1.76 [1.21-2.51] and 1.00 [0.46-1.86] mg kg-1, respectively. The drug combination for hypnosis produced a supra-additive interaction. Hypnosis time was significantly shorter in the groups given the mixtures compared to each hypnotic administered alone. After repeated injections, hypnosis time with the mixtures showed smaller prolongation than that with the hypnotic alone. Flumazenil completely restored the recovery time after anesthesia. The combination of JM-1232(-) and propofol showed a supra-additive interaction, and the reduced hypnotic dose contributed to a faster recovery even after multiple injections.

Dexmedetomidine and hydroxyzine synergistically potentiate the hypnotic activity of propofol in mice

PURPOSE

Investigation into the characteristics of anesthetic interactions may provide clues to anesthesia mechanisms. Dexmedetomidine, an α(2)-adrenergic receptor agonist, has become a popular sedative in intensive care, and hydroxyzine, a histamine receptor antagonist, is well known as a tranquilizing premedication for anesthesia. However, no experimental or pharmacological evaluation has been reported concerning their combination with propofol. Thus, we studied their combined effect with a hypnotic dose of propofol in ddY mice.

METHODS

Male adult mice were intravenously administered either dexmedetomidine (30 μg/kg) or hydroxyzine (5 mg/kg) with propofol (3.75-10 mg/kg) to induce hypnosis, defined as a loss of the righting reflex (LRR). Other mice were intravenously administered propofol, dexmedetomidine (300 μg/kg), or hydroxyzine (50 mg/kg) alone, and subsequent behavioral changes were observed. The 50% effective dose (ED(50)) for LRR was calculated, and the duration of LRR was determined.

RESULTS

The hypnotic dose of propofol was 9.95 ± 1.04 mg/kg (ED(50) ± SEM) without combination. Dexmedetomidine and hydroxyzine reduced the ED(50) of propofol to 5.32 ± 0.57 and 5.63 ± 0.57 mg/kg, respectively. Coadministration of dexmedetomidine significantly extended LRR duration compared with propofol alone, whereas hydroxyzine significantly shortened LRR duration. A maximal dose of dexmedetomidine or hydroxyzine alone did not induce hypnosis.

CONCLUSIONS

Dexmedetomidine and hydroxyzine demonstrated no hypnotic action alone; however, their coadministration potentiated the hypnotic activity of propofol. Although reduction in the dose of propofol was similar, only dexmedetomidine prolonged the duration of hypnosis.

[(11)C]flumazenil positron emission tomography analyses of brain gamma-aminobutyric acid type A receptors in Angelman syndrome

OBJECTIVE

To evaluate the role of the gamma-aminobutyric acid type A (GABA(A)) receptor in Angelman syndrome (AS).

STUDY DESIGN

We performed [(11)C]flumazenil positron emission tomography (PET) and examined GABA(A) receptor expression in 7 patients with AS of various genotypes (5 with the deletion, 1 with an imprinting defect [ID], and 1 with a UBE3A mutation) and 4 normal control healthy volunteers.

RESULTS

Relative to the control subjects, the [(11)C]flumazenil binding potentials (BPs) were significantly higher in the cerebral cortex and cerebellum in the 5 patients with the deletion and in the 1 patient with a UBE3A mutation, and were less frequently or barely increased in adult patients with the deletion and in the patient with IDs.

CONCLUSIONS

Total GABA(A) receptor expression was increased in patients with AS with various genotypes. We suggest that a developmental dysregulation of the GABA(A) receptor subunits occurs in patients with AS.

An investigation of flumazenil to antagonize gamma-hydroxybutyrate intoxication in a murine model

OBJECTIVE

Prior animal studies have suggested that flumazenil may blunt GHB's sedative-hypnotic affects. We hypothesized that flumazenil would decrease the affects of GHB in a murine model of intoxication.

METHODS

We performed a controlled, pilot experiment using 32 mice divided into 3 groups. All mice received intraperitoneal injections of GHB (1.5 g/kg). Group I received sham injections at time 0, and then GHB at 5 minutes. Group II received flumazenil (0.3 mg/kg) at time 0, and then GHB at 5 minutes. Group III received sham injection at time 0, then GHB at 5 minutes, and then 4 escalating flumazenil doses administered at 3-minute intervals (0.003 to 1 mg/kg). We measured certain functions: time to loss/recovery of righting reflexes (RR), time to sprawl/recovery of sprawl (postural tone [PT]), and death.

RESULTS

There were statistically significant delays in the loss of PT and shortened recovery time to RR in pre-treated mice (group II) versus controls (group I). There were no differences in group III versus group I for any outcome parameters.

CONCLUSIONS

In this model, pre-dosing flumazenil prior to GHB administration delayed clinical intoxication.