Ratiometric determination of etomidate based on an albumin-based indicator displacement assay (IDA).

The first fluorescent sensor based on the indicator displacement assay (IDA) for on-site determination of etomidate.

Predicting Treatment Response in Primary Aldosteronism Using 11 C-Metomidate Positron Emission Tomography.

BACKGROUND: Appropriate treatment of primary aldosteronism (PA) depends on accurate lateralization. 11 C-metomidate (MTO) is a tracer used in PET that provides functional information about the adrenal cortex. We aimed to perform MTO PET for patients with PA who are managed according to the guideline and to verify its correlation with other lateralization modalities and usefulness in outcome prediction. METHODS: Seventeen patients with PA who underwent MTO PET and had ≥1 lateralization modality (adrenal venous sampling and/or NP-59 adrenal scintigraphy) were included. SUV max of each adrenal gland (higher uptake side, HSUV max ; lower uptake side, LSUV max ) and the ratio of HSUV max to LSUV max (contrast) were compared with lateralization modalities, postsurgical outcomes, and medical treatment outcomes. Cutoff values were used as outcome predictors. RESULTS: HSUV max and LSUV max increased in the order of bilateral, unilateral, and negative findings of CT, with opposite order of contrast. High discordant rate between MTO PET and other lateralization modalities was noted. Biochemical responders (n = 8) had significantly lower HSUV max and LSUV max than nonresponders, and clinical responders (n = 6) had borderline lower HSUV max than nonresponders. By optimal cutoff values of HSUV max and LSUV max , MTO PET was able to predict biochemical and clinical outcomes in patients with medical treatment. CONCLUSION: According to adrenal CT findings, MTO PET presented different uptake patterns. Patients with PA under medical treatment showed significantly lower tracer uptake in responders. Thus, MTO PET may be a useful imaging biomarker to predict medical treatment outcome. Multicenter prospective study with a larger number of patients is needed for further validation.

11C-Metomidate PET-CT versus adrenal vein sampling to subtype primary aldosteronism: a prospective clinical trial.

OBJECTIVE: Adrenal vein sampling (AVS) is recommended to subtype primary aldosteronism, but it is technically challenging. We compared 11C-Metomidate-PET-computed tomography (PET-CT) and AVS for subtyping of primary aldosteronism. METHODS: Patients with confirmed primary aldosteronism underwent both AVS and 11C-Metomidate PET-CT (post-dexamethasone). All results were reviewed at a multidisciplinary meeting to decide on final subtype diagnosis. Primary outcome was accuracy of PET versus AVS to diagnosis of unilateral primary aldosteronism based on post-surgical biochemical cure. Secondary outcome was accuracy of both tests to final subtype diagnosis. RESULTS: All 25 patients recruited underwent PET and successful AVS (100%). Final diagnosis was unilateral in 22 patients, bilateral in two and indeterminate in one due to discordant lateralization. Twenty patients with unilateral primary aldosteronism underwent surgery, with 100% complete biochemical success, and 75% complete/partial clinical success. For the primary outcome, sensitivity of PET was 80% [95% confidence interval (95% CI): 56.3-94.3] and AVS was 75% (95% CI: 50.9-91.3). For the secondary outcome, sensitivity and specificity of PET was 81.9% (95% CI: 59.7-94.8) and 100% (95% CI: 15.8-100), and AVS was 68.2% (95% CI: 45.1-86.1) and 100% (95% CI: 15.8-100), respectively. Twelve out of 20 (60%) patients had both PET and AVS lateralization, four (20%) PET-only, three (15%) AVS-only, while one patient did not lateralize on PET or AVS. Post-surgery outcomes did not differ between patients identified by either test. CONCLUSION: In our pilot study, 11C-Metomidate PET-CT performed comparably to AVS, and this should be validated in larger studies. PET identified patients with unilateral primary aldosteronism missed on AVS, and these tests could be used together to identify more patients with unilateral primary aldosteronism. VIDEO ABSTRACT: http://links.lww.com/HJH/B918.

A Novel Etomidate Analog EL-0052 Retains Potent Hypnotic Effect and Stable Hemodynamics without Suppressing Adrenocortical Function.

Etomidate is a potent and rapidly acting anesthetic with high therapeutic index (TI) and superior hemodynamic stability. However, side effect of suppressing adrenocortical function limits its clinical use. To overcome this side effect, we designed a novel etomidate analog, EL-0052, aiming to retain beneficial properties of etomidate and avoid its disadvantage of suppressing adrenocortical steroid synthesis. Results exhibited that EL-0052 enhanced GABAA receptors currents with a concentration for EC50 of 0.98 ± 0.02 µM, which was about three times more potent than etomidate (3.07 ± 1.67 µM). Similar to hypnotic potency of etomidate, EL-0052 exhibited loss of righting reflex with ED50s of 1.02 (0.93-1.20) mg/kg in rats and 0.5 (0.45-0.56) mg/kg in dogs. The TI of EL-0052 in rats was 28, which was higher than 22 of etomidate. There was no significant difference in hypnotic onset time, recovery time, and walking time between EL-0052 and etomidate in rats. Both of them had minor effects on mean arterial pressure in dogs. EL-0052 had no significant effect on adrenocortical function in dogs even at a high dose (4.3 × ED50), whereas etomidate significantly inhibited corticosteroid secretion. The inhibition of cortisol synthesis assay showed that EL-0052 had a weak inhibition on cortisol biosynthesis in human H259 cells with an IC50 of 1050 ± 100 nM, which was 2.09 ± 0.27 nM for etomidate. EL-0052 retains the favorable properties of etomidate, including potent hypnotic effect, rapid onset and recovery, stable hemodynamics, and high therapeutic index without suppression of adrenocortical function. SIGNIFICANCE STATEMENT: The novel etomidate analog EL-0052 retains the favorable properties of etomidate without suppressing adrenocortical function and provides a new strategy to optimize the structure of etomidate.

Fast and reliable analysis of veterinary metomidate and etomidate in human blood samples by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in a postmortem case.

Metomidate and etomidate belong to the non-barbiturate imidazole family of sedative-hypnotics and elicit little analgesic action when used alone. Metomidate, in particular, has little analgesic activity in humans and is, therefore, used for veterinary purposes. In 2019, a Korean woman in her twenties was found unconscious in a motel bath and eventually died. Etomidate, alprazolam, escitalopram, and metomidate were detected in the postmortem specimens. To our knowledge, this is the first case of human metomidate abuse reported in the Republic of Korea. In this research, a simple and reliable method was developed for the analysis of metomidate and etomidate in human blood samples using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Blood samples were deproteinized with acetonitrile, filtered, and analyzed by LC-MS/MS. Linear calibration curves were obtained with six concentrations ranging from 1 to 50 ng/ml for metomidate and 10 to 500 ng/ml for etomidate. The method was validated by assessing the selectivity, linearity, limit of detection (LOD), limit of quantitation (LOQ), intra- and inter-day precision and accuracy, matrix effect, and stability and successfully applied to the analysis of metomidate and etomidate in human blood samples. In a postmortem case, the concentrations of metomidate and etomidate were found to be 8 and 110 ng/ml in femoral blood and 6 and 210 ng/ml in cardiac blood, respectively.

Preliminary Investigations into Use of Metomidate for Euthanasia of Ornamental Fishes.

The goals of this study were to investigate the potential use of metomidate for one-step euthanasia of ornamental fish species representing commonly sold families in the ornamental fish trade and to determine a baseline euthanasia dose for most species tested. Metomidate hydrochloride, a rapid-acting, water-soluble, nonbarbiturate hypnotic related to etomidate, was tested at various concentrations and durations for euthanasia of species representing the following freshwater and marine aquarium fish families: Apogonidae, Ariidae, Blenniidae, Callichthyidae, Characidae, Cichlidae, Cyprinidae, Gobiidae, Gyrinocheilidae, Loricariidae, Melanotaeniidae, Osphronemidae, Pimelodidae, Poeciliidae, Pomacentridae, and Pseudochromidae. Fish in each trial were euthanized as a group (n = 1). Most groups contained 10-12 fish. Some higher doses required buffering. Euthanasia was considered successful if all fish in each group did not recover after 6 h in unmedicated water. All species immediately lost buoyancy and equilibrium, dropping to the tank bottom within 1 min and ceasing ventilation typically within minutes. However, reactivity to vibration, sound, or touch was noticeable for varying time periods afterward (8-66 min), so an additional 30 min of exposure after cessation of reactivity was included as part of the protocol. Although some species (Neon Tetras Paracheirodon innesi and Australian Rainbowfish Melanotaenia australis) were euthanized at a concentration of 40 mg/L metomidate for a total exposure time of 38 min, most species tested were successfully euthanized with metomidate at a concentration of 100 mg/L, with total exposure times ranging from 35-96 min. A few catfish species (Otocinclus sp. and Bronze Corydoras Corydoras aeneus) were refractory and recovered after 100 mg/L. However, Otocinclus sp. were successfully euthanized at 250 mg/L, and Bronze Corydoras were euthanized at 1,000 mg/L. Further studies are needed to provide additional data for these and other species and families, for different water chemistry conditions, and for various biological factors to fine-tune dosing regimens.

Para-chloro-2-[18F]fluoroethyl-etomidate: A promising new PET radiotracer for adrenocortical imaging.

Introduction: [11C]Metomidate ([11C]MTO), the methyl ester analogue of etomidate, was developed as a positron emission tomography (PET) radiotracer for adrenocortical tumours and has also been suggested for imaging in primary aldosteronism (PA). A disadvantage of [11C]MTO is the rather high non-specific binding in the liver, which impacts both visualization and quantification of the uptake in the right adrenal gland. Furthermore, the short 20-minute half-life of carbon-11 is a logistic challenge in the clinical setting. Objectives: The aim of this study was to further evaluate the previously published fluorine-18 (T1/2=109.5 min) etomidate analogue, para-chloro-2-[18F]fluoroethyl etomidate; [18F]CETO, as an adrenal PET tracer. Methods: In vitro experiments included autoradiography on human and cynomolgus monkey (non-human primate, NHP) tissues and binding studies on adrenal tissue from NHPs. In vivo studies with [18F]CETO in mice, rats and NHP, using PET and CT/MRI, assessed biodistribution and binding specificity in comparison to [11C]MTO. Results: The binding of [18F]CETO in the normal adrenal cortex, as well as in human adrenocortical adenomas and adrenocortical carcinomas, was shown to be specific, both in vitro (in humans) and in vivo (in rats and NHP) with an in vitro Kd of 0.66 nM. Non-specific uptake of [18F]CETO in NHP liver was found to be low compared to that of [11C]MTO. Conclusions: High specificity of [18F]CETO to the adrenal cortex was demonstrated, with in vivo binding properties qualitatively surpassing those of [11C]MTO. Non-specific binding to the liver was significantly lower than that of [11C]MTO. [18F]CETO is a promising new PET tracer for imaging of adrenocortical disease and should be evaluated further in humans.

Modeling the Effect of Excitation on Depth of Anesthesia Monitoring in γ-Aminobutyric Acid Type A Receptor Agonist ABP-700.

BACKGROUND: γ-Aminobutyric acid type A (GABAA) receptor agonists are known to cause involuntary muscle movements. The mechanism of these movements is not known, and its relationship to depth of anesthesia monitoring is unclear. We have explored the effect of involuntary muscle movement on the pharmacokinetic-pharmacodynamic model for the GABAA receptor agonist ABP-700 and its effects on the Bispectral Index (BIS) as well as the Modified Observer's Assessment of Alertness/Sedation (MOAA/S) scores. METHODS: Observations from 350 individuals (220 men, 130 women) were analyzed, comprising 6,312 ABP-700 concentrations, 5,658 ABP-700 metabolite (CPM-acid) concentrations, 25,745 filtered BIS values, and 6,249 MOAA/S scores, and a recirculatory model developed. Various subject covariates and pretreatment with an opioid or a benzodiazepine were explored as covariates. Relationships between BIS and MOAA/S models and involuntary muscle movements were examined. RESULTS: The final model shows that the pharmacokinetics of ABP-700 are characterized by small compartmental volumes and rapid clearance. The BIS model incorporates an effect-site for BIS suppression and a secondary excitatory/disinhibitory effect-site associated with a risk of involuntary muscle movements. The secondary effect-site has a threshold that decreases with age. The MOAA/S model did not show excitatory effects. CONCLUSIONS: The GABAA receptor agonist ABP-700 shows the expected suppressive effects for BIS and MOAA/S, but also disinhibitory effects for BIS associated with involuntary muscle movements and reduced by pretreatment. Our model provides information about involuntary muscle movements that may be useful to improve depth of anesthesia monitoring for GABAA receptor agonists.

11C-Metomidate PET/CT Detected Multiple Ectopic Adrenal Rest Tumors in a Woman With Congenital Adrenal Hyperplasia.

CONTEXT: Women with congenital adrenal hyperplasia (CAH) may present with androgen excess that is difficult to control with conventional suppressive doses of glucocorticoids. Clinical management is challenging, and the woman is at great risk of developing steroid-induced complications. PATIENTS AND METHODS: A 32-year-old woman with salt-wasting CAH due to 21-hydroxylase deficiency underwent right-sided adrenalectomy because of a large myelolipoma. Over the years, androgens became increasingly difficult to suppress on prednisolone 5 + 0 + 2.5 mg daily, and at age 39 years the left adrenal with an enlarging myelolipoma was removed. A month later serum testosterone levels had increased from 4.1 preoperatively to 18.3 nmol/L (reference 0.2-1.8 nmol/L), and adrenocorticotropin levels from 32 to 283 pmol/L (reference < 14 pmol/L). No adrenal parenchyma was visualized on computed tomography (CT). In the further search for the source of the markedly elevated testosterone, positron emission tomography (PET) was performed with 2 different tracers, 18fluorodeoxyglucose (18FDG) reflecting glucose metabolism and 11C-metomidate, an inhibitor of 11-ß-hydroxylase targeting adrenocortical tissue. RESULTS: 18FDG-PET/CT with cosyntropin stimulation showed ovarian/paraovarian hypermetabolism, suggestive of adrenal rest tumors. Further characterization with 11C-metomidate PET/CT showed uptakes localized to the ovaries/adnexa, behind the spleen, and between the right crus diaphragmaticus and inferior vena cava. CONCLUSION: Adrenal rest tumors can give rise to high androgen levels in spite of suppressive supraphysiological glucocorticoid doses. This case illustrates, for the first time, the value of 11C-metomidate PET as a sensitive method in documenting adrenal rest tumors, currently considered rare in women with CAH.

Functional imaging of adrenal cortex. / Estudios de imagen funcional de la corteza adrenal.

The rising number of high-resolution imaging scans has increased the adrenal lesions detection, which require a differential diagnosis. Currently, the most commonly used scans are CT and MRI, but these are sometimes not very specific. In these cases, nuclear medicine scans with 131I-norcolesterol, 11C-metomidate and 18F-fludeoxyglucose help to differentiate benign vs. malignant lesions, to lateralize the involvement in hypersecretion disease, as well as to guide the therapeutic strategy in both unilateral and bilateral lesions.

11C-metomidate PET in the diagnosis of adrenal masses and primary aldosteronism: a review of the literature.

BACKGROUND: Adrenal masses are commonly encountered in clinical practice, many of whom are incidental. Identifying malignancy, and excess hormone production is essential for appropriate management. Biochemical workup and imaging tests (dedicated adrenal CT and/or MRI) are used to determine the likelihood of excessive hormone function and malignancy, respectively. However, imaging cannot provide information about function and biochemical workup cannot localize the source. Furthermore, in primary aldosteronism, adrenal vein sampling, the gold standard for lateralization, has important limitations such as the technical expertise required, the elevated costs, and potential complications. Over the last decades, there has been a renewed interest in alternative noninvasive imaging techniques that provide information about adrenal function without the need for invasive procedures. In this review, we will evaluate the evidence and the potential role of 11C-metomidate as a promising positron emission tomography (PET) tracer in clinical practice. METHODS: A review of the English literature for articles describing the use of the tracer 11C-metomidate in adrenal disorders. RESULTS: A total of 12 studies were included in the systematic review, which altogether addressed the use of 11C-metomidate in adrenal masses and the application of this tracer in primary aldosteronism. CONCLUSIONS: 11C-metomidate, a selective inhibitor of 11-ß-hydroxylase, demonstrated a high specificity for adrenocortical tissue. In addition, 11C-metomidate is correlated with this enzyme activity making it a potentially useful PET tracer for the identification primary aldosteronism, in addition to detection of adrenocortical masses.

New insights for screening etomidate analogues in the human H295R cell model.

Etomidate is a sedative-hypnotic with excellent pharmacological effects, including rapid onset and hemodynamic stability. However, etomidate causes adrenocortical toxicity via binding to 11ß-hydroxylase. Therefore, developing an approach to screen new etomidate analogues without endocrine-disrupting effects is urgently warranted. In this study, we employed the adrenocortical tumour cell line, NCI-H295R, as an in vitro system for etomidate analogues screening and detected the hormone levels in these cells using a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method. After obtaining the concentration-response curves of hormone release, the "Adrenocortical Inhibitory Index" was used to evaluate the adrenocortical inhibitory potency of each compound. In summary, we demonstrate the benefits of our methods for screening of etomidate analogues that lack adrenocortical suppression, especially when this in vitro system is combined with in vivo testing.

Non-clinical single- and repeated-dose toxicity studies of ET-26 hydrochloride in rats.

ET-26 hydrochloride (ET-26HCl), a novel analog of etomidate, induces as effective sedation, with good cardiac and respiratory stability, as etomidate but with mild adrenocortical suppression. The objective of this study was to evaluate the potential adverse effects of ET-26HCl in rats. In a single-dose toxicity study, abnormal urine color (red) was observed in all groups: control (100%), 8 mg/kg (10%), 16 mg/kg (50%), and 20 mg/kg (70%) ET-26HCl, which returned to normal on the day of dosing. There were no mortalities or serious toxicological signs; the maximum tolerable dose of ET-26HCl was 20 mg/kg. In the repeated-dose toxicity study, deaths occurred in the 12- (13.33% of males) and 16-mg/kg/day (20% of males and 3.33% of females) groups. Abnormal urine color (red or brown) was detected in the control group (10%) and all treatment groups (30%, 46.67%, and 40% at 8, 12 and 16 mg/kg/day, respectively), at a frequency of 1.43% in the control group, 4.76% in 8 mg/kg/day, 7.62% in 12 mg/kg/day, and 4.29% in 16 mg/kg/day. Increases in neutrophils and plasma fibrinogen were temporary and recoverable effects. Macroscopic and histopathologic changes were found only at the injection sites: abnormal skin color, scabbing, thrombus, ulceration, and inflammation. During the recovery period, there was evidence of reversibility, including fibroblast proliferation and vessel recanalization. The no-observed-adverse-effect level of ET-26HCl was 8 mg/kg/day. Toxicokinetic variables of ET-26HCl, except the calculated initial concentration in females on Day 1, showed a dose-dependent increase to exposure, with no gender difference and no evidence of accumulation.

Preclinical safety evaluation of ET-26 hydrochloride, a novel intravenous anesthetic agent, in beagle dogs.

ET-26 hydrochloride (ET-26HCl) is a novel etomidate analogue, approved for clinical trials, which has an effective sedative-hypnotic effect, a stable myocardial performance, and milder adrenocortical suppression than etomidate in rats and beagle dogs. Additionally, ET-26HCl showed similar hemodynamic stability as etomidate in the rat uncontrolled hemorrhagic shock model. Furthermore, ET-26HCl, in the rat lipopolysaccharide-induced sepsis model, was found to have a higher survival rate, a lower inflammatory reaction, and less organ injury. In the present study, we measured the potential adverse effects of ET-26HCl in beagle dogs in accordance with the Guidance on single- and repeated-dose toxicity published by the China Food and Drug Administration. In toxicity studies, single and repeated (14 days) intravenous doses of up to 16 mg/kg were well tolerated, with only pharmacologically related clinical signs seen in both studies. Thus, the no-observed-adverse-effect level (NOAEL) of ET-26HCl was found at 16 mg/kg/day. Toxicokinetic examination demonstrated that ET-26HCl showed a dose-dependent increase to exposure, no gender difference, and no evidence of accumulation. These results provide useful information for guiding a phase I clinical trial of ET-26HCl in healthy volunteers.

Preclinical Pharmacokinetics Study of a Novel Intravenous Anesthetic ET-26 Hydrochloride.

BACKGROUND: ET-26 hydrochloride is a novel intravenous anesthetic, approved for clinical trials, that produces a desirable sedative-hypnotic effect with stable myocardial performance and mild adrenocortical suppression in rats and beagle dogs. The objective of this study was to assess the absorption, distribution, metabolism, and excretion of ET-26 hydrochloride. METHODS: Hepatocytes from human, monkey, dog, rat, and mouse were used to determine the metabolites of ET-26 hydrochloride. Distribution and excretion were assessed in rats and pharmacokinetic studies were performed in beagle dogs. RESULTS: The metabolic pathway and proposed structure of metabolites were fully assessed resulting from the biotransformation reactions of hydrolysis, dehydrogenation, demethylation and glucuronic acid conjugation. The main distribution of the drug was in fat (15067 ± 801 ng/ml) and liver (13647 ± 1126 ng/ml), and the kidney was the primary excretion route (4.47%-11.94%). The Cmax after injection with 1.045 mg/kg, 2.09 mg/kg, and 4.18 mg/kg was 1476.5 ± 138.9 ng/ml, 2846.1 ± 223.3 ng/ml, and 6233.3 ± 238.9 ng/ml, respectively. The t1/2 of the drug was similar across dose groups at 74.8 ± 10.8 min to 81.4 ± 4.2 min. The AUC0-t values were 30208.1 ± 2026.5 min*ng/ml, 62712.8 ± 1808.3 min*ng/ml, and 130465.2 ± 7457.4 min*ng/ml, respectively. CONCLUSION: The metabolic pathway and the proposed structure of metabolites for ET-26 hydrochloride were fully assessed. The majority of distribution for ET-26 hydrochloride occurs in the fat and liver, while the primary route of excretion for ET-26 hydrochloride is through the kidney. In dogs, pharmacokinetic features of ET-26 hydrochloride had a linear relationship with dosage.

Behavioral and steroidogenic pharmacology of phenyl ring substituted etomidate analogs in rats.

BACKGROUND: Cushing's syndrome is an endocrine disorder characterized by the overproduction of adrenocortical steroids. Steroidogenesis enzyme inhibitors are the mainstays of pharmacological treatment. Unfortunately, they produce significant side effects. Among the most potent inhibitors is the general anesthetic etomidate whose GABAA receptor-mediated sedative-hypnotic actions restrict use. In this study, we defined the sedative-hypnotic and steroidogenesis inhibiting actions of etomidate and four phenyl-ring substituted etomidate analogs (dimethoxy-etomidate, isopropoxy-etomidate, naphthalene-etomidate, and naphthalene (2)-etomidate) that possess negligible GABAA receptor modulatory activities. METHODS: In the first set of experiments, male Sprague-Dawley rats were assessed for loss of righting reflexes (LoRR) after receiving intravenous boluses of either etomidate (1 mg/kg) or an etomidate analog (40 mg/kg). In the second set of experiments, rats were assessed for LoRR and their abilities to produce adrenocortical and androgenic steroids after receiving 2-h infusions (0.5 mg kg- 1 min- 1) of either etomidate or an etomidate analog. RESULTS: All rats that received etomidate boluses or infusions had LoRR that persisted for minutes or hours, respectively. In contrast, no rat that received an etomidate analog had LoRR. Compared to rats in the vehicle control group, rats that received etomidate analog infusions had plasma corticosterone and aldosterone concentrations that were reduced by 80-84% and 68-94%, respectively. Rats that received etomidate infusions had plasma corticosterone and aldosterone concentrations that were also significantly reduced (by 92 and 96%, respectively). Rats that received etomidate or isopropoxy-etomidate had significant reductions (90 and 57%, respectively) in plasma testosterone concentrations whereas those that received naphthalene-etomidate had significant increases (1400%) in plasma dehydroepiandrosterone concentrations. Neither etomidate nor any etomidate analog significantly affected plasma androstenedione and dihydrotestosterone concentrations. CONCLUSIONS: Our studies demonstrate that the four phenyl-ring substituted etomidate analogs form a novel class of compounds that are devoid of sedative-hypnotic activities and suppress plasma concentrations of adrenocortical steroids but vary in their effects on plasma concentrations of androgenic steroids.

Toxicologic and Inhibitory Receptor Actions of the Etomidate Analog ABP-700 and Its Metabolite CPM-Acid.

BACKGROUND: The etomidate analog ABP-700 produces involuntary muscle movements that could be manifestations of seizures. To define the relationship (if any) between involuntary muscle movements and seizures, electroencephalographic studies were performed in Beagle dogs receiving supra-therapeutic (~10× clinical) ABP-700 doses. γ-aminobutyric acid type A (GABAA) and glycine receptor studies were undertaken to test receptor inhibition as the potential mechanism for ABP-700 seizures. METHODS: ABP-700 was administered to 14 dogs (6 mg/kg bolus followed by a 2-h infusion at 1 mg · kg(-1) · min(-1), 1.5 mg · kg(-1) · min(-1), or 2.3 mg · kg(-1) · min(-1)). Involuntary muscle movements were documented, electroencephalograph was recorded, and plasma ABP-700 and CPM-acid concentrations were measured during and after ABP-700 administration. The concentration-dependent modulatory actions of ABP-700 and CPM-acid were defined in oocyte-expressed α1ß3γ2L GABAA and α1ß glycine receptors (n = 5 oocytes/concentration) using electrophysiologic techniques. RESULTS: ABP-700 produced both involuntary muscle movements (14 of 14 dogs) and seizures (5 of 14 dogs). However, these phenomena were temporally and electroencephalographically distinct. Mean peak plasma concentrations were (from lowest to highest dosed groups) 35 µM, 45 µM, and 102 µM (ABP-700) and 282 µM, 478 µM, and 1,110 µM (CPM-acid). ABP-700 and CPM-acid concentration-GABAA receptor response curves defined using 6 µM γ-aminobutyric acid exhibited potentiation at low and/or intermediate concentrations and inhibition at high ones. The half-maximal inhibitory concentrations of ABP-700 and CPM-acid defined using 1 mM γ-aminobutyric acid were 770 µM (95% CI, 590 to 1,010 µM) and 1,450 µM (95% CI, 1,340 to 1,560 µM), respectively. CPM-acid similarly inhibited glycine receptors activated by 1 mM glycine with a half-maximal inhibitory concentration of 1,290 µM (95% CI, 1,240 to 1,330 µM). CONCLUSIONS: High dose ABP-700 infusions produce involuntary muscle movements and seizures in Beagle dogs via distinct mechanisms. CPM-acid inhibits both GABAA and glycine receptors at the high (~100× clinical) plasma concentrations achieved during the dog studies, providing a plausible mechanism for the seizures.

11 C-Metomidate PET/CT is a useful adjunct for lateralization of primary aldosteronism in routine clinical practice.

OBJECTIVE: To describe clinical practice experience of 11 C-Metomidate PET/CT as an adjunct to adrenal vein sampling (AVS) in the lateralization of aldosterone-producing adenomas (APA) in primary aldosteronism (PA). CONTEXT: Accurate lateralization of APA in the setting of PA offers the potential for surgical cure and improved long-term cardiovascular outcomes. Challenges associated with AVS, the current gold standard lateralization modality, mean that only a small proportion of potentially eligible patients currently make it through to surgery. This has prompted consideration of alternative strategies for lateralization, including the application of novel molecular PET tracers such as 11 C-Metomidate. DESIGN: Clinical Service Evaluation/Retrospective audit. PATIENTS: Fifteen individuals with a confirmed diagnosis of PA, undergoing lateralization with 11 C-Metomidate PET/CT prior to final clinical decision on surgical vs medical management. MEASUREMENTS: All patients underwent screening aldosterone renin ratio (ARR), followed by confirmatory testing with the seated saline infusion test, according to Endocrine Society Clinical Practice Guidelines. Adrenal glands were imaged using dedicated adrenal CT. 11 C-Metomidate PET/CT was undertaken due to equivocal or failed AVS. Management outcomes were assessed by longitudinal measurement of blood pressure, ARR, number of hypertensive medications following adrenalectomy or institution of medical therapy. RESULTS: We describe the individual lateralization and clinical outcomes for 15 patients with PA. CONCLUSION: 11 C-Metomidate PET/CT in conjunction with adrenal CT and AVS provided useful information which aided clinical decision-making for PA within a multidisciplinary hypertension clinic.