The inhibition by etomidate of the 11 beta-hydroxylation of cortisol

Dimethoxy-etomidate: A Nonhypnotic Etomidate Analog that Potently Inhibits Steroidogenesis

Cushing's syndrome is characterized by the overproduction of adrenocortical steroids. Steroidogenesis inhibitors are mainstays of medical therapy for Cushing's syndrome; unfortunately, adverse side effects and treatment failures are common with currently available drugs. The general anesthetic induction agent etomidate is among the most potent inhibitors of adrenocortical steroidogenesis. However, its use as a treatment of Cushing's syndrome is complicated by its sedative-hypnotic activity and ability to produce myoclonus, central nervous system actions thought to be mediated by the GABA_A receptor. Here, we describe the pharmacology of the novel etomidate analog (R)-ethyl 1-(1-(3,5-dimethoxyphenyl)ethyl)-1H-imidazole-5-carboxylate (dimethoxy-etomidate). In contrast to etomidate, dimethoxy-etomidate minimally enhanced GABA-evoked GABA_A receptor-mediated currents even at a near-saturating aqueous concentration. In Sprague-Dawley rats, dimethoxy-etomidate's potency for producing loss of righting reflexes-an animal model of sedation/hypnosis-was 2 orders of magnitude lower than that of etomidate, and it did not produce myoclonus. However, similar to etomidate, dimethoxy-etomidate potently suppressed adrenocortical steroid synthesis primarily by inhibiting 11β-hydroxylase. [³H]etomidate binding to rat adrenocortical membranes was inhibited by dimethoxy-etomidate in a biphasic manner with IC₅₀ values of 8.2 and 3970 nM, whereas that by etomidate was monophasic with an IC₅₀ of 22 nM. Our results demonstrate that, similar to etomidate, dimethoxy-etomidate potently and dose-dependently suppresses adrenocortical steroid synthesis by inhibiting 11β-hydroxylase. However, it is essentially devoid of etomidate's GABA_A receptor positive modulatory and sedative-hypnotic activities and produces no myoclonus, providing proof of concept for the design of etomidate analogs without important central nervous system actions for the pharmacologic treatment of Cushing's syndrome.

Sedative-hypnotic Binding to 11β-hydroxylase

BACKGROUND

Etomidate potently suppresses adrenocortical steroid synthesis with potentially deleterious consequences by binding to 11β-hydroxylase and inhibiting its function. The authors hypothesized that other sedative-hypnotics currently in clinical use or under development (or their metabolites) might bind to the same site at clinically relevant concentrations. The authors tested this hypothesis by defining etomidate's affinity for this site and the potencies with which other sedative-hypnotics (and their metabolites) inhibit etomidate binding.

METHODS

H-etomidate's binding to adrenal membranes from Sprague-Dawley rats was characterized with a filtration assay, and its dissociation constant was defined using saturation and homologous ligand competition approaches. Half-inhibitory concentrations of sedative-hypnotics and metabolites were determined from the reduction in specific H-etomidate binding measured in the presence of ranging sedative-hypnotic and metabolite concentrations.

RESULTS

Saturation and homologous competition studies yielded H-etomidate dissociation constants of 40 and 21 nM, respectively. Half-inhibitory concentrations of etomidate and cyclopropyl methoxycarbonyl metomidate (CPMM) differed significantly (26 vs. 143 nM, respectively; P < 0.001), and those of the carboxylic acid (CA) metabolites etomidate-CA and CPMM-CA were greater than or equal to 1,000× higher than their respective parent hypnotics. The half-inhibitory concentration of dexmedetomidine was 2.2 µM, whereas those of carboetomidate, ketamine, and propofol were greater than or equal to 50 µM.

CONCLUSION

Etomidate's in vitro dissociation constant for 11β-hydroxylase closely approximates its in vivo adrenocortical half-inhibitory concentration. CPMM produces less adrenocortical suppression than etomidate not only because it is metabolized faster but also because it binds to 11β-hydroxylase with lower affinity. Other sedative-hypnotics and metabolites bind to 11β-hydroxylase and inhibit etomidate binding only at suprahypnotic concentrations.

The Treatment of Cushing's Disease

Cushing's disease (CD), or pituitary-dependent Cushing's syndrome, is a severe endocrine disease caused by a corticotroph pituitary tumor and associated with increased morbidity and mortality. The first-line treatment for CD is pituitary surgery, which is followed by disease remission in around 78% and relapse in around 13% of patients during the 10-year period after surgery, so that nearly one third of patients experience in the long-term a failure of surgery and require an additional second-line treatment. Patients with persistent or recurrent CD require additional treatments, including pituitary radiotherapy, adrenal surgery, and/or medical therapy. Pituitary radiotherapy is effective in controlling cortisol excess in a large percentage of patients, but it is associated with a considerable risk of hypopituitarism. Adrenal surgery is followed by a rapid and definitive control of cortisol excess in nearly all patients, but it induces adrenal insufficiency. Medical therapy has recently acquired a more important role compared to the past, due to the recent employment of novel compounds able to control cortisol secretion or action. Currently, medical therapy is used as a presurgical treatment, particularly for severe disease; or as postsurgical treatment, in cases of failure or incomplete surgical tumor resection; or as bridging therapy before, during, and after radiotherapy while waiting for disease control; or, in selected cases, as primary therapy, mainly when surgery is not an option. The adrenal-directed drug ketoconazole is the most commonly used drug, mainly because of its rapid action, whereas the glucocorticoid receptor antagonist, mifepristone, is highly effective in controlling clinical comorbidities, mainly glucose intolerance, thus being a useful treatment for CD when it is associated with diabetes mellitus. Pituitary-directed drugs have the advantage of acting at the site responsible for CD, the pituitary tumor. Among this group of drugs, the dopamine agonist cabergoline and the somatostatin analog pasireotide result in disease remission in a consistent subgroup of patients with CD. Recently, pasireotide has been approved for the treatment of CD when surgery has failed or when surgery is not an option, and mifepristone has been approved for the treatment of Cushing's syndrome when associated with impairment of glucose metabolism in case of the lack of a surgical indication. Recent experience suggests that the combination of different drugs may be able to control cortisol excess in a great majority of patients with CD.

Adrenocortical suppression and recovery after continuous hypnotic infusion: etomidate versus its soft analogue cyclopropyl-methoxycarbonyl metomidate

Introduction

Etomidate is no longer administered as a continuous infusion for anesthetic maintenance or sedation, because it results in profound and persistent suppression of adrenocortical steroid synthesis with potentially lethal consequences in critically ill patients. We hypothesized that rapidly metabolized soft analogues of etomidate could be developed that do not produce persistent adrenocortical dysfunction even after prolonged continuous infusion. We hope that such agents might also provide more rapid and predictable anesthetic emergence. We have developed the soft etomidate analogue cyclopropyl-methoxycarbonyl etomidate (CPMM). Upon termination of 120-minute continuous infusions, hypnotic and encephalographic recoveries occur in four minutes. The aims of this study were to assess adrenocortical function during and following 120-minute continuous infusion of CPMM and to compare the results with those obtained using etomidate.

Methods

Dexamethasone-suppressed rats were randomized into an etomidate group, CPMM group, or control group. Rats in the etomidate and CPMM groups received 120-minute continuous infusions of etomidate and CPMM, respectively. Rats in the control group received neither hypnotic. In the first study, adrenocortical function during hypnotic infusion was assessed by administering adrenocorticotropic hormone (ACTH) 90 minutes after the start of the hypnotic infusion and measuring plasma corticosterone concentrations at the end of the infusion 30 minutes later. In the second study, adrenocortical recovery following hypnotic infusion was assessed by administering ACTH every 30 minutes after infusion termination and measuring plasma corticosterone concentrations 30 minutes after each ACTH dose.

Results

During hypnotic infusion, ACTH-stimulated serum corticosterone concentrations were significantly lower in the CPMM and etomidate groups than in the control group (100 ± 64 ng/ml and 33 ± 32 ng/ml versus 615 ± 265 ng/ml, respectively). After hypnotic infusion, ACTH-stimulated serum corticosterone concentrations recovered to control values within 30 minutes in the CPMM group but remained suppressed relative to those in the control group for more than 3 hours in the etomidate group.

Conclusions

Both CPMM and etomidate suppress adrenocortical function during continuous infusion. However, recovery occurs significantly more rapidly following infusion of CPMM.

Medical suppression of hypercortisolemia in Cushing's syndrome with particular consideration of etomidate

Cushing's syndrome is associated with excessive cortisol secretion by the adrenal gland or ectopic tumours and may result in diabetes, hypertension, and life-threatening infections with high mortality rates especially in the case of surgical resection. Although surgical resection is the treatment of choice, patients may benefit from preceding medical therapy. This may especially be useful as an adjunctive approach in emergency settings, if patients cannot undergo surgery, if surgery or radiotherapy fails, or if the tumour recurs. Medical therapy can be categorized in three different groups-inhibition of steroidogenesis, suppression of adrenocorticotropic hormone, and antagonism of the glucocorticoid receptor. However, the majority of common drugs are not available for parenteral administration, which may evoke a management problem in emergency settings or in patients unable to tolerate oral medication. The carboxylated imidazole etomidate is a well known parenteral induction agent for general anaesthesia. Besides its hypnotic properties, etomidate also has α-adrenergic characteristics and inhibits the enzyme 11-deoxycortisol ß-hydroxylase, which catalyzes the final step of the conversion of cholesterol to cortisol. Adverse outcomes have been reported when used for sedation in septic or trauma patients probably by its interference with steroid homeostasis. However, its capability of inhibition of the 11-deoxycortisol ß-hydroxylase leads to suppression of cortisol secretion which has been demonstrated to be a useful tool in severe and complicated hypercortisolemia. Within this article, we review the data concerning different pharmacological approaches with particular consideration of etomidate in order to suppress steroidogenesis in patients with Cushing's syndrome.

Differential effects of etomidate and its pyrrole analogue carboetomidate on the adrenocortical and cytokine responses to endotoxemia

OBJECTIVE

We developed a novel pyrrole analog of etomidate, (R)-ethyl 1-(1-phenylethyl)-1H-pyrrole-2-carboxylate (carboetomidate), which retains etomidate's desirable anesthetic and hemodynamic properties but lacks its potent inhibitory affect on adrenocorticotropic hormone-stimulated steroid synthesis. The objective of this study was to test the hypothesis that in contrast to etomidate, carboetomidate neither suppresses the adrenocortical response to endotoxemia nor enhances the accompanying production of proinflammatory cytokines.

DESIGN

Animal study.

SETTING

University research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

For both single and multiple anesthetic dose studies, rats were injected with Escherichia coli lipopolysaccharide immediately followed by a hypnotic dose of etomidate, carboetomidate, or vehicle alone (dimethyl sulfoxide) as a control. For single-dose studies, no additional anesthetic (or vehicle) was administered. For multiple anesthetic dose studies, additional doses of anesthetic (or vehicle) were administered every 15 mins for a total of eight anesthetic (or vehicle) doses.

MEASUREMENTS AND MAIN RESULTS

Plasma adrenocorticotropic hormone, corticosterone, and cytokine concentrations were measured before lipopolysaccharide administration and intermittently throughout the 5-hr experiment. In single anesthetic dose studies, plasma adrenocorticotropic hormone and cytokine concentrations were not different at any time point among the etomidate, carboetomidate, and vehicle groups, whereas plasma corticosterone concentrations were briefly (60-120 mins) reduced in the etomidate group. In multiple anesthetic dose studies, plasma corticosterone concentrations were persistently lower and peak plasma interleukin-1β and interleukin-6 concentrations were higher in the etomidate group vs. the carboetomidate and control groups. Peak plasma interleukin-10 concentrations were similarly elevated in the etomidate and carboetomidate groups vs. the control group.

CONCLUSIONS

Compared with etomidate, carboetomidate produces less suppression of adrenocortical function and smaller increases in proinflammatory cytokine production in an endotoxemia model of sepsis. These findings suggest that carboetomidate could be a useful alternative to etomidate for maintaining anesthesia for a prolonged period of time in patients with sepsis.

Etomidate revisited

The major advantage of etomidate is its lack of cardiovascular side effects. In addition, etomidate is supposed to be neuroprotective. The side effects of etomidate include adrenal suppression and myocloni. A review of the recent literature on etomidate, its clinical use, its side effects and its mechanism of action was performed. Among others, major recent advances include a new drug preparation devoid of propylene glycol and its side effects, a new pretreatment technique that may reduce the incidence of myocloni, and the identification of its site of action in the central nervous system.

Etomidate- ® Lipuro is associated with considerably less injection pain in children compared with propofol with added lidocaine

BACKGROUND

Propofol is associated with a high incidence of injection pain in children, even if given together with lidocaine. A new lipid formulation of etomidate (Etomidate-Lipuro) has been found in adults to cause very little discomfort during i.v. injection. The aim of the present prospective, double-blind, randomized trial was to compare the incidence of injection pain during i.v. induction of anaesthesia between propofol with added lidocaine (previous standard) and this new etomidate formulation in paediatric patients.

METHODS

A total of 110 paediatric patients, aged 2-16 years, scheduled for outpatient surgery were planned to be included in the study. The primary end point of the study was the incidence of injection pain during induction of anaesthesia as assessed by a four-point scale as described previously. The occurrence of myoclonic muscular activity was registered as a secondary end point (four-point scale). An interim analysis after 80 patients was requested by the Ethics' Committee.

RESULTS

The study was stopped after the inclusion of 80 patients. A significantly lower incidence of injection pain was found in the Etomidate-Lipuro group as compared with the propofol-lidocaine group (5.0% vs 47.5%, P<0.001). The use of etomidate was associated with a significantly higher incidence of myoclonic activity compared with propofol-lidocaine (85.0% vs 15%, P<0.001).

CONCLUSIONS

The use of a new lipid formulation of etomidate is associated with significantly less injection pain than propofol with added lidocaine in children. This finding may warrant a change in clinical practice in order to avoid unnecessary pain in children.

Etomidate-facilitated hip reduction in the emergency department

Joint dislocations are common presenting complaints in emergency departments (EDs). Dislocations of major joints, such as the shoulder, elbow, and hip, are often difficult to gently reduce because of the challenge in obtaining sufficient relaxation of large muscle groups. This is the first reported use of etomidate to assist in the reduction of a major joint in an outpatient setting. We discuss the case of an elderly woman with total hip arthroplasty who experienced four spontaneous posterior hip dislocations in a 5-month period. Narcotics and benzodiazepines failed to facilitate reduction at every encounter, whereas etomidate made the procedure easy the two times it was used in the ED. This article reviews the administration of etomidate for conscious sedation and discusses potential complications.

Etomidate and telazol

These two drugs, etomidate and Telazol, have different pharmacological properties. The good properties of these drugs should be employed in specific patients and procedures to be performed (Table 3). There is no ideal injectable agent available yet for clinical practice. This in itself makes practice quite interesting because of the continuous process of rationalizing and determining the best drug for a specific condition and patient.

A review of etomidate for rapid sequence intubation in the emergency department

Currently, there is no one drug that is the agent of choice for induction in rapid sequence intubation in the emergency department (ED). All agents currently used as induction agents in the ED offer distinct advantages for various clinical conditions, but each has a significant side effect profile and specific contraindications that limit its use in many common clinical settings. A review of the data available from the anesthesia literature suggests that etomidate possesses many properties that may make it the agent of choice for rapid sequence intubations in the ED. These advantages include excellent pharmacodynamics, protection from myocardial and cerebral ischemia, minimal histamine release, and a hemodynamic profile that is uniquely stable. Disadvantages include a lack of blunting of sympathetic response to intubation, a high incidence of myoclonus, prominent nausea and vomiting, potential activation of seizures in patients with epileptogenic foci, and impaired glucocorticoid response to stress. Further studies are needed to evaluate the advantages and disadvantages of the use of etomidate for rapid sequence intubation in the ED.

Anaesthesia for cardioversion

Cardioversion is a minor procedure requiring sedation and analgesia. However, it is often performed out-of-hours in remote sites by inexperienced anaesthetists. An understanding is required both of the pathophysiology underlying cardiac arrhythmias and of the technical side of defibrillation equipment, including electrical safety. Patients should have their coagulation status and electrolyte balance checked prior to the procedure to reduce the likelihood of complications. Almost all the available anaesthetic agents have been used for cardioversion in the past, with varying degrees of success. The anaesthetic agent chosen for patients undergoing cardioversion must provide analgesia and sedation, cause the least cardiovascular compromise possible and still enable rapid recovery. Propofol may be the closest anaesthetic agent to this ideal currently available, although careful titration of any agent chosen is also important. Cardioversion may be performed as an emergency, including in the pregnant patient, providing safe anaesthetic practice is followed.

Preferential inhibition of mouse hepatic coumarin 7-hydroxylase by inhibitors of steroid metabolizing monooxygenases

Etomidate, metomidate and metyrapone, all potent inhibitors of steroid metabolizing monooxygenases, inhibit preferentially coumarin 7-hydroxylase (COH) amongst several liver microsomal monooxygenase activities from control and pyrazole-treated D2 mice in vitro. SKF-525A, an inhibitor of phenobarbital-inducible monooxygenase activities has a much weaker effect on COH than the other three drugs, even though COH is a phenobarbital-inducible enzyme. Treatment of mice with eto- and metomidate decreases the microsomal COH also in vivo while the other activities remained unchanged (with the exception of 7-ethoxycoumarin O-deethylase (ECDE) in case of metomidate). Despite of the decrease in COH no parallel decrease in the amount of microsomal P450Coh (P450 isoenzyme highly active in the 7-hydroxylation of coumarin) could be found in dot immuno-binding analysis. These data suggest that among several liver microsomal P450 isoenzymes, metyrapone, eto- and metomidate interact preferentially with the P450Coh and that eto- and metomidate may alter selectively the catalytic properties of P450Coh leading to decreased enzyme activity. Two different Ks-values could be found for all three drug in their binding to microsomal cytochrome(s) P450. Based on substrate binding spectra, potassium ferricyanide treatment does not dissociate the complex between reduced P450 and metomidate and does it only partly for etomidate. Furthermore potassium ferricyanide treatment of microsomes does not increase COH after in vivo treatment of mice with eto- and metomidate. These data further suggest that the complex between P450Coh and eto- and metomidate may be particularly strong and independent from the redox state of the haem iron.

Cardiovascular instability following bolus dose of etomidate

A patient with alveolar proteinosis developed unexpected cardiovascular instability after broncho-alveolar lavage. He had received two bolus doses of etomidate within an 18-hour period. Serum cortisol concentrations were low and hydrocortisone replacement therapy was necessary to restore arterial pressure. Implications for management of critically ill patients who receive bolus doses of etomidate are discussed.

[Hormonal changes induced by etomidate in children during the first 24 postoperative hours]

The hormonal effects of an etomidate infusion were assessed postoperatively in children undergoing hypospadias or clubfoot repair. The study was carried out in 12 children, aged between 9 and 70 months, randomly assigned to two equal groups. The anaesthetic protocol was identical for all the children, consisting in a light general anaesthesia (halothane induction, intubation after 60 to 80 micrograms.kg-1 vecuronium) combined with lumbar epidural anaesthesia (initial dose of 0.75 ml.kg-1 bupivacaine with adrenaline, with repeat injections of half the previous dose when there was a change in the haemodynamic parameters suggesting inadequate analgesia). Anaesthetic maintenance was different in both groups: 1 to 1.5 vol% enflurane in a nitrous oxide-oxygen mixture (1/1 v/v) in the control group, and 16.8 +/- 3.0 mg.kg-1.min-1 etomidate infusion in the etomidate group. Venous blood samples were collected after induction of anesthesia (before starting the epidural anaesthesia and the etomidate infusion), at the end of surgery (H0), at the 3rd (H3), 6th (H6), 12th (H12) and 24th h (H24) following surgery. The following hormonal blood concentrations were measured: cortisol, 11 beta-desoxycortisol, aldosterone, 11 beta-desoxycorticosterone, dehydroepiandrosterone (DHA) and DHA sulphate (DHA-S). In the control group, cortisol and DHA-S concentrations decreased significantly at H0, aldosterone levels also being significantly lower at H24. In the etomidate group, cortisol concentrations remained significantly lower at H0, H3 and H6; aldosterone concentrations were also significantly lower than control values throughout the study period. There was an important prolonged rise in the concentrations of their precursors. DHA and DHA-S concentrations did not change in the etomidate group.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-adrenal action of a subanaesthetic dose of etomidate

The effects of subanaesthetic doses of etomidate on corticosteroid synthesis have been studied in vivo. In the group of patients who received etomidate (n = 10), cortisol and aldosterone responses to adrenocorticotrophic hormone were blunted, while 11-de-oxycortisol response was increased, as compared to a control group (n = 10). These results suggest that a single bolus of 0.04 mg/kg etomidate, which produces sedation, without loss of consciousness, is able to block adrenal 11 hydroxylase.

Nonhypnotic low-dose etomidate for rapid correction of hypercortisolaemia in Cushing's syndrome

We determined the adrenostatic potential of low-dose nonhypnotic etomidate in six patients with Cushing's syndrome (ectopic Cushing's syndrome, n = 2; Cushing's disease, n = 3; bilateral adrenal adenoma, n = 1). Etomidate was given as a continuous infusion for 32 h in a dose of 2.5 mg/h (n = 5) or 0.3 mg/kg/h (n = 3), respectively. Saline was given during a control period. The responsiveness to exogenous ACTH was studied during placebo and 7 and 31 h after commencing etomidate by administration of 250 micrograms 1-24 ACTH i.v. Etomidate (2.5 mg/h) led to a consistent decrease in serum cortisol in all patients from a mean of 39.4 +/- 13.3 to 21.1 +/- 5.7 micrograms/dl after 7 h (P less than 0.05 compared with placebo). After 24 h cortisol was reduced further to a mean steady state concentration of 12.3 +/- 5.7 micrograms/dl (P less than 0.05). At the end of the infusion period the cortisol increase in response to ACTH was reduced but not abolished. In contrast, a dose of 0.3 mg/kg/h etomidate induced unresponsiveness of serum cortisol to exogenous ACTH within 7 h. However, sedation was observed in two out of three patients at this dose, while during etomidate in a dose of 2.5 mg/h no side effects were seen. We conclude that low-dose nonhypnotic etomidate reduces serum cortisol to within the normal range in patients with Cushing's syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)

Hormonal effects of an induction dose of etomidate for patients undergoing urgent myocardial revascularization

The use of etomidate for induction of anesthesia in patients requiring urgent coronary artery surgery provides good cardiovascular stability. However, long-term etomidate infusions may cause transient signs of adrenocortical suppression. The purpose of this study was to determine whether an induction bolus dose of etomidate would cause clinically relevant endocrine dysfunction in urgent coronary artery bypass patients. With institutional review board approval, 11 patients were prospectively randomized to a diazepam (control) or etomidate rapid sequence induction. The diazepam group (n=6; mean, 69 years) received 0.4 mg/kg of diazepam. The etomidate group (n=5; mean, 54 years) received 0.3 mg/kg of etomidate. Maintenance anesthesia included nitrous oxide, oxygen, pancuronium, and fentanyl in increments up to 32 microg/kg. Hemodynamics, cortisol, epinephrine, and norepinephrine were measured both intraoperatively and postoperatively. The only significant difference between the two groups in hemodynamic parameters was a higher heart rate in the etomidate group. Both agents adequately controlled the stress response to intubation as judged from the levels of epinephrine, norepinephrine. and cortisol. However, in both groups epinephrine and norepinephrine increased between intubation and removal of the aortic cross-clamp. Cortisol also increased from the time of cross-clamp removal to 12 and 24 hours post-bypass. During anesthesia and surgery in the pre-bypass period, there was a decrease in cortisol over time in the etomidate group, and there was an increase with diazepam. Thus, etomidate provided stable hemodynamics, possible mild intraoperative adrenocortical suppression, a depressed hormonal stress response to intubation, and a normal hormonal reaction to the later part of surgery and the postoperative period.

Adrenocortical suppression and other endocrine effects of etomidate

(+/-) Etomidate is a short-acting general anaesthetic given by the intravenous route. It has strong adrenal suppression capability initially shown in the rat and then observed in man. At present, the drug seems the most effective adrenocortical inhibitor on a molar basis in vitro. 11 beta-hydroxylase is the most sensitive target enzyme; 16 alpha-, 17 alpha-hydroxylase and cholesterol side-chain cleavage are inhibited by higher concentrations. (+) Etomidate was more active than the (+/-) and far more than the (-) stereoisomer. Etomidate blood concentrations greatly exceed those needed to block adrenal steroidogenesis both when used inappropriately by infusion for long-term sedation (such previously unrecognized drug-induced adrenal suppression has often proved fatal in severely-injured patients) and also when given in very low doses as an induction anaesthetic. Reactive ACTH increase is currently observed. Etomidate, in vivo, does not appear to affect testicular steroidogenesis although it shares an imidazole moiety with fungicide phenylimidazoles endowed with such an action. However, testosterone production may be reduced by high concentrations in vitro. Other gonadal hormones seem unchanged. Both basal and stress-induced blood prolactin levels are lowered by etomidate in the rat but probably not in man arguably through interference at brain level where the GABA-benzodiazepine receptor complex could be directly involved. Hence, endocrine and neuroendocrine interferences are unique non-anaesthetic effects of etomidate.

Effect of ketoconazole, etomidate and other inhibitors of steroidogenesis on cytochrome P-450sccII-catalyzed reactions

The effects of a variety of certain inhibitors of adrenal steroidogenesis have been studied on the reconstituted C21-steroid 17 alpha-hydroxylase-17,20-lyase system, whose protein components, the enzyme 17 alpha-hydroxylase-17,20-lyase(P-450sccII) and its reductase, are extensively purified from pig testis microsomes. We found: (1) Ketoconazole (cis-1-acetyl-4-[4-((2-(2,4-dichlorophenyl)-2-(1H-imidazole-1- ylmethyl-1,3-dioxalan-4-ol)methoxy)phenyl] piperazine and Etomidate(R-(+)-ethyl-[1-(a-methyl-benzyl)-indol-5-carboxylatel), inhibited cleavage of 17 alpha-hydroxy progesterone at the 17,20-bond to give androstenedione in a dose-dependent fashion. (2) Some other inhibitors of steroidogenesis, Metyrapone (2-methyl-1.2di-3-pyridyl-1-propanone), Trilostane (4,5-epoxy-17-hydroxy-3-oxo androstane-2-carbonitrile),o,p'DDD (1-(O-chlorophenyl)-1-(p-chlorophenyl)2,2-dichloroethane) and Aminoglutethimide (p-(alpha-aminopheny)-alpha-ethylglutaramide) did not inhibit the same 17,20-lyase system. (3) All of the above listed inhibitors, over a wide variety of concentration ranges, had no significant effect on the 17 alpha-hydroxylation of 11 beta-hydroxyprogesterone, which had been shown to be catalyzed by the same P-450sccII. (4) NADPH:P-450 reductase was not inhibited by all of the above listed inhibitors.

Influence of induction of anaesthesia with midazolam on the neuro-endocrine response to surgery

The effect of midazolam, for induction of anaesthesia, on the glycaemic and adrenocortical responses to lower pelvic surgery in female patients has been studied and compared with a comparable group of patients receiving thiopentone. Although midazolam has been shown to obtund adrenaline and noradrenaline release to electrical or surgical stress in the rat and dog, there was no blunting of the glycaemic response to surgery in man. Plasma cortisol levels in response to surgery and anaesthesia were comparable in the two groups of patients.

Missing effect of etomidate on testosterone secretion in man

We studied the effect of low dosage (0.26 mg/kg as a single induction dose) and high dosage (30 mg/h for long term sedation) etomidate on serum testosterone and serum luteinizing hormone (LH) concentrations in males. During high dose etomidate we found inhibition of both 11 beta-hydroxylase and cholesterol-side-chain cleavage enzyme with unresponsiveness of progesterone, 17 alpha OH-progesterone and 11-deoxycortisol to stimulation with ACTH. However, neither high dosage nor low dosage etomidate had any influence on serum testosterone or LH concentrations. We conclude that, in contrast to other substituted imidazole derivatives, etomidate does not interfere with testicular testosterone synthesis. It therefore may be possible to find clinically useful imidazole derivatives with endocrine actions confined to either the adrenals or the testes.

Effects of cortisol suppression by etomidate on changes in circulating metabolites associated with pelvic surgery

The effects of cortisol suppression by etomidate on the changes in circulating metabolites associated with pelvic surgery were investigated in healthy female patients. The use of etomidate resulted in the inhibition of cortisol secretion for 24 h compared with a control group of patients. However, the inhibition of steroidogenesis was not associated with a significant effect on blood glucose, blood lactate and plasma nonesterified fatty acid values, although the glycaemic response to surgery was consistently less in those patients who received etomidate. Heart rate and arterial pressure were significantly decreased during surgery in the etomidate group compared with the control group, but were similar in the postoperative period when the difference in plasma cortisol between the groups was greatest. The results suggest that cortisol has only a minor role in determining changes in circulating metabolites associated with surgery.

Effects of etomidate on cortisol biosynthesis in isolated guinea-pig adrenal cells: comparison with metyrapone

The effects of the iv hypnotic etomidate on cortisol biosynthesis have been investigated in short term incubations of dispersed guinea-pig adrenal cells and were compared with those produced by metyrapone. Fifty percent inhibition of cortisol output was obtained at a final medium concentration of 3.5 10(-8) M (basal), 2.8 10(-8) M (ACTH-stimulated) for etomidate and of 5.10(-7) M (stimulated) for metyrapone. In the presence of etomidate, 11-deoxycortisol at 5.10(-8) M reached a peak value of 244 +/- 11% of control (mean +/- SE, n = 7). 17 alpha-Hydroxyprogesterone and progesterone were not significantly affected up to 10(-7) M, but at higher concentrations, all three precursors fell under their control values. Metyrapone induced a progressive rise of 11-deoxycortisol, from 10(-7) M upwards, to a maximum level at 10(-5) M (210 +/- 15% of control, mean +/- SE, n = 5). 17-Hydroxyprogesterone and progesterone concentrations were not significantly modified by metyrapone. The less active hypnotic L-enantiomer of etomidate had almost no inhibitory effect on cortisol production. The results obtained so far suggest that etomidate is a potent inhibitor of the mitochondrial cytochrome P-450 enzymes of the adrenal cortex, mainly the 11 beta-hydroxylase. At higher dose the cholesterol side-chain cleavage enzyme system seemed also to be affected.

Effect of a single bolus of etomidate upon eight major corticosteroid hormones and plasma ACTH

In a prospective controlled trial we investigated the effect of an induction dose of etomidate (0.26 mg/kg i.v.) on plasma ACTH, progesterone, 17 alpha OH-progesterone, 11-deoxycortisol, cortisol, cortisone, corticosterone, 11-deoxycorticosterone, and aldosterone in seven males undergoing general anaesthesia. Seven other male patients receiving thiopentone at induction (5.0 mg/kg i.v.) served as controls. Plasma ACTH concentrations rose higher in the etomidate group (346 +/- 124 vs. 117 +/- 74 pg/ml, mean +/- SEM), but the difference was not significant. After etomidate we found a clear suppression of plasma cortisol (P less than 0.01), cortisone (P less than 0.01), corticosterone (P less than 0.01), and aldosterone (P less than 0.05) compared to corticosteroid levels after induction with thiopentone. Plasma 11-deoxycortisol and 11-deoxycorticosterone concentrations were grossly elevated 210 min after etomidate (91 +/- 28 nmol/l and 7.04 +/- 0.47 nmol/l, respectively, P less than 0.01) demonstrating inhibition of 11 beta-hydroxylation of both glucocorticoid and mineralocorticoid intermediates. In contrast, no significant difference in plasma progesterone and 17 alpha-OH-progesterone levels was found between the two groups indicating that the cholesterol-side-chain cleavage enzyme is less sensitive to etomidate than 11 beta-hydroxylase. Our results suggest that after induction of anaesthesia with a single bolus of etomidate, inhibition of other enzymes in the corticosteroid-synthetic pathway (e.g. cholesterol-side-chain cleavage enzyme) is of little clinical relevance.

Peri-operative endocrine effects of etomidate

This study investigated the effects of etomidate on endocrine responses to anaesthesia and surgery. Patients undergoing abdominal hysterectomy received standard anaesthetics of either etomidate for induction with etomidate infusion, or thiopentone and halothane. Etomidate suppressed the secretion of cortisol and aldosterone for between 8 and 22 hours after the end of the etomidate infusion; 11-deoxycortisol secretion was not suppressed during the etomidate infusion, but rose postoperatively; 17 alpha-hydroxyprogesterone suppression also lasted only as long as the etomidate infusion. There were no effects on plasma oestradiol, ACTH, or prolactin, but growth hormone concentrations were elevated in the etomidate group. Etomidate was concluded to have influenced adrenocortical function only, where it probably inhibits 11 beta-hydroxylation, 17 alpha-hydroxylation and other intramitochondrial hydroxylation reactions. There were no clinical sequelae attributable to adrenocortical suppression. The relationship of chemical structure of etomidate and other phenylated imidazoles to inhibition of steroidogenesis is discussed.

On the site of action of the anti-adrenal steroidogenic effect of etomidate and megestrol acetate

The sites of action of the anti-steroidogenic action of etomidate and megestrol acetate have been established with a novel in vitro approach based upon the inhibition of cortisol (Co) secretion by dispersed guinea-pig adrenal cells. The cells were challenged with the Co precursor steroids (all at 10(-5) mol/l) pregnenolone (Pe), 17-hydroxy-pregnenolone (17-Pe), progesterone (Po), 17-hydroxyprogesterone (17-Po), 21-deoxycortisol (21-DOC) and 11-deoxycortisol (11-DOC), or 1-24 adrenocorticotrophin (ACTH, 100 ng/l) in the presence or absence of either etomidate, megestrol acetate, metyrapone or trilostane (all at 5 X 10(-5) mol/l). In the absence of drug, the steroid precursors or ACTH provoked a cortisol secretion of greater than 14 times that secreted by cells incubated in their absence. ACTH-stimulated Co secretion was inhibited by greater than 85% by all the drugs employed. In the presence of trilostane and megestrol acetate, Co secretion provoked by the delta 4 3-keto steroids (Po, 17-Po, 21-DOC and 11-DOC) was similar to the controls. However, with the delta 5, 3 beta-hydroxy steroids, 17-Pe and Pe, Co secretion was inhibited by greater than 57% in the presence of these drugs. In contrast, etomidate and metyrapone inhibited Co secretion by greater than 60% when 11-deoxycortisol was employed, indicative of a block at 11 beta-hydroxylase, the final step in the cortisol biosynthetic pathway. Similar results were seen with Pe, 17-Pe, Po and 17-Po, all of which are converted to cortisol via a biosynthetic route which includes catalysis by 11 beta-hydroxylase.(ABSTRACT TRUNCATED AT 250 WORDS)

Etomidate: a selective adrenocortical 11 beta-hydroxylase inhibitor

To investigate the adrenocortical suppression caused by the anesthetic etomidate, plasma levels of progesterone (P), 17-hydroxyprogesterone (17-OHP), 11-deoxycorticosterone (DOC), corticosterone (B), aldosterone (Aldo), 11-deoxycortisol (S), cortisol (F), and cortisone (E) were measured simultaneously before and after a short-term ACTH stimulation test in a 6.5-year-old boy whose convulsions could be kept under control only with constant etomidate infusions. During etomidate therapy, plasma levels of DOC and S were extremely elevated, the progestins P and 17-OHP were slightly elevated, whereas B and Aldo were in the lower normal range, and F and E were markedly decreased. A short-term ACTH stimulation test during etomidate infusion gave a blunted response of B, Aldo, F and E, whereas the level of DOC remained high and S even further increased. P and 17-OHP showed a positive response to ACTH. The ratios of B/DOC and F/S, which reflect adrenocortical 11 beta-hydroxylase activity, were extremely decreased during etomidate and did not change after ACTH stimulation. In contrast, the ratios of DOC/P and S/17-OHP, which reflect 21-hydroxylase activity, were elevated and remained elevated after ACTH stimulation. After discontinuation of etomidate therapy, all the baseline steroid levels were somewhat elevated, but responded normally to ACTH. These results demonstrate that etomidate causes a specific and reversible blockade of the 11 beta-hydroxylation of adrenal steroid synthesis.