In vitro and in vivo characterisation of the metabolism and disposition of suvorexant in humans

Preclinical metabolism and the disposition of vornorexant/TS-142, a novel dual orexin 1/2 receptor antagonist for the treatment of insomnia

We investigated the metabolism and disposition of vornorexant, a novel dual orexin receptor antagonist, in rats and dogs, and clarified in vitro metabolite profiles in humans. Furthermore, we investigated the pharmacokinetics of active metabolites in rats and dogs and their CNS distribution in rats to elucidate its contribution to drug efficacy. [14 C]vornorexant was rapidly and mostly absorbed after the oral administration in rats and dogs. The drug-derived radioactivity, including metabolites, was distributed to major organs such as the liver, kidneys in rats, and was almost eliminated within 24 h post-dose in both species. Metabolite profiling revealed that main clearance mechanism of vornorexant was metabolism via multiple pathways by oxidation. The major circulating components were the cleaved metabolites (M10, M12) in rats, and the unchanged form in dogs, followed by M1, and then M3. Incubation with human hepatocytes resulted in formation of metabolites, including M1, M3, M10, and M12. The metabolic pathways were similar in all tested species. Resulting from the PK and CNS distribution of active metabolites (M1 and M3) with weaker pharmacological activity, the concentration of the unchanged form was higher than that of active metabolites in rat CSF and dog plasma, suggesting that the unchanged form mainly contributed to the drug efficacy. These findings demonstrate that vornorexant is absorbed immediately after administration, and vornorexant and its metabolites are rapidly and completely eliminated in rats and dogs. Thus, vornorexant may have favorable pharmacokinetic profiles as a hypnotic drug to provide rapid onset of action and minimal next-day residual effects in humans.

Effect of lemborexant on pharmacokinetics of clozapine: A potential drug-drug interaction mediated by time-dependent inhibition of CYP3A4

Clozapine (CLZ) is extensively used for treatment-resistant schizophrenia (TRS) with caution to avoid serious adverse events such as agranulocytosis and drug-drug interactions (DDIs). In the current report, we present a case of a 35-year-old male non-smoking TRS patient whose steady-state plasma trough concentrations (Ctrough ) of CLZ and its active metabolite, N-desmethylclozapine (NDMC), were significantly increased after initiating oral administration of lemborexant (LEM), a dual orexin receptor antagonist, for the treatment of insomnia. The patient experienced oversedation with sleepiness and fatigue while maintaining high levels of Ctrough of CLZ. The increased concentrations of CLZ returned to normal ranges after the discontinuation of LEM dosing, implying a pharmacokinetic DDI between CLZ and LEM. To gain insight into possible mechanisms, we performed in vitro assays of CYP1A2- and CYP3A4-mediated CLZ metabolism by measuring the formations of NDMC and clozapine N-oxide (CNO). In accordance with previous studies, the incubation of CLZ with each enzyme resulted in the production of both metabolites. LEM had only a weak inhibitory effect on CYP1A2- and CYP3A4-mediated CLZ metabolism. However, the preincubation of LEM with CYP3A4 in the presence of NADPH showed a significant enhancement of inhibitory effects on CLZ metabolism with IC50 values for the formations of CNO and NDMC of 2.8 μM and 4.1 μM, respectively, suggesting that LEM exerts as a potent time-dependent inhibitor for CYP3A4. Taken together, the results of the current study indicate that co-medication of CLZ with LEM may lead to increase in exposure to CLZ and risks of CLZ-related adverse events.

Quantification of Suvorexant in Human Urine Using a Validated HPTLC Bioanalytical Method

Suvorexant (SUV) is a new sedative/hypnotic medicine that is recommended to treat insomnia. It is an important medicine from a forensic point of view due to its sedative/hypnotic and depressant effects. To the best of our knowledge, high-performance thin-layer chromatography (HPTLC) bioanalytical methods have not been published to measure SUV in human urine and pharmaceutical samples. Accordingly, this study was designed and validated a sensitive and rapid bioanalytical HPTLC method to determine SUV in human urine samples for the very first time. The densitometric measurement of SUV and the internal standard (IS; sildenafil) was performed on glass-coated silica gel normal-phase-60F254S TLC plates using a mixture of chloroform and methanol (97.5:2.5 v/v) as the eluent system. Both the SUV and IS were detected at a wavelength of 254 nm. Both analytes were extracted using the protein precipitation technique utilizing methanol as the solvent. For the IS and SUV, the Rf values were 0.09 and 0.45, respectively. The proposed bioanalytical method for SUV was linear in the 50-1600 ng/band range. The current bioanalytical technique was linear, precise (% RSD = 3.28-4.20), accurate (% recovery = 97.58-103.80), robust (% recovery = 95.31-102.34 and % RSD = 2.81-3.15), rapid, and sensitive (LOD = 3.73 ng/band and LOQ = 11.20 ng/band). These findings suggested that the current bioanalytical method can be regularly used to determine SUV in wide varieties of urine samples.

Suvorexant, a Novel Dual Orexin Receptor Antagonist, for the Management of Insomnia

Purpose of Review

The present investigation is a comprehensive review regarding the use of Suvorexant for insomnia treatment. It covers the background, pathophysiology, and significance of addressing insomnia, the pharmaceutical details of Suvorexant, and its safety, efficacy, and implications in treating insomnia. We further discuss Suvorexant's role in targeting insomnia with other comorbidities.

Recent Findings

Insomnia refers to poor quality and/or quantity of sleep. While there are many existing treatments such as benzodiazepines, melatonin agonists, TCAs, and atypical antipsychotics used to target various receptors involved in normal induction and maintenance of sleep, Suvorexant is an antagonist that specifically targets orexin receptors. Recent clinical studies suggest that Suvorexant is both clinically safe and effective. Quantity and quality of sleep are measured in various ways, yet the consensus points towards Suvorexant's effectiveness in improving sleep time, onset, latency, and quality compared to placebo. In addition to helping improve isolated insomnia, Suvorexant helps improve sleep in patients that have other comorbidities such as obstructive sleep apnea, Alzheimer's disease, dementia, acute stroke, and delirium. While Suvorexant is safe, there are still adverse effects associated with the drug that needs to be considered. The most common adverse effects include dizziness, somnolence, headaches, and cognitive impairment.

Summary

Insomnia is a major public health concern that affects many people worldwide and has been linked to many adverse health outcomes. While there are existing treatments that target different receptors and pathways of normal sleep induction and maintenance, Suvorexant is a novel drug that targets dual orexin receptors. Its safety and efficacy, mechanism of action, pharmacokinetic parameters, and relative lack of rebound and withdrawal effects render suvorexant a reliable choice for the treatment of insomnia.

Effect of gastric pH and of a moderate CYP3A4 inducer on the pharmacokinetics of daridorexant, a dual orexin receptor antagonist

AIM

Daridorexant is a dual orexin receptor antagonist developed for the treatment of insomnia. The solubility of daridorexant is pH dependent and daridorexant has been shown to be a sensitive CYP3A4 substrate when co-administered with moderate CYP3A4 inhibitors. The purpose of this study was to assess the effect of an increased gastric pH on daridorexant pharmacokinetics (PK) and the extent of interaction when daridorexant is co-administered with a moderate CYP3A4 inducer.

METHODS

In this prospective, single-centre, randomized, open-label study, 24 male subjects consecutively received four treatments, i.e., daridorexant 50 mg single dose; famotidine 40 mg single dose + daridorexant 50 mg single dose; efavirenz 600 mg once a day (o.d.) during 10 days; and daridorexant 50 mg single dose + efavirenz 600 mg o.d. for 2 days. Plasma PK parameters of daridorexant were derived by noncompartmental analysis. Standard safety and tolerability evaluations were analysed descriptively.

RESULTS

When daridorexant administration was preceded by administration of famotidine, daridorexant C_max decreased by 39%, geometric means ratio (GMR) (90% confidence interval (90% CI)): 0.61 (0.50, 0.73). AUC_0-∞ remained unchanged. In the presence of steady-state efavirenz, daridorexant C_max , AUC_0-∞ , and t_½ decreased by approximately 35% (GMR (90% CI)): 0.65 (0.54, 0.78), 61% (0.39 (0.348, 0.44), and 35% (0.65 (0.58, 0.73), respectively. T_max remained unaffected. All treatments containing daridorexant were well tolerated.

CONCLUSION

Daridorexant 50 mg can be administered concomitantly with gastric pH modifiers or with moderate CYP3A4 inducers without dose adaptation based on efficacy observed at lower doses in Phase 3 studies.

Effect of severe renal impairment on pharmacokinetics, safety, and tolerability of lemborexant

The primary aim of this study was to examine the effect of severe renal impairment (SRI) on the pharmacokinetics of lemborexant, a dual orexin receptor antagonist indicated for the treatment of insomnia. A phase 1 multicenter, single‐dose, open‐label, parallel‐group study was conducted in subjects with SRI not requiring dialysis (estimated glomerular filtration rate 15–29 ml/min/1.73 m²; n = 8) compared with demographically matched healthy subjects with normal renal function (n = 8). Plasma levels of lemborexant and its metabolites were measured over 240 h following a single oral 10‐mg dose administered in the morning. Relative to subjects with normal renal function, lemborexant maximum plasma concentration (C_max) was similar, whereas area under the plasma concentration–time curve from zero to time of last quantifiable concentration (AUC_(0‐t)) and AUC from zero to infinity (AUC_(0‐inf)) were about 1.5‐fold higher in subjects with SRI. The geometric mean ratios (90% confidence interval) were 104.8 (77.4–142.0), 150.5 (113.2–200.3), and 149.8 (113.1–198.6) for C_max, AUC_(0‐t), and AUC_(0‐inf), respectively. In both groups, the median lemborexant time to C_max (t_max) was 1 h, and the mean unbound fraction of lemborexant was ~7%. For the M4, M9, and M10 metabolites, C_max was reduced ~20% and exposure (AUC_(0‐t) and AUC_(0‐inf)) was ~1.4‐ to 1.5‐fold higher in subjects with SRI versus healthy subjects; t_max was delayed ~1.5–2 h for M4 and M10. All treatment‐emergent adverse events were mild or moderate. Lemborexant pharmacokinetics were not sufficiently altered to warrant a dose adjustment for subjects with renal impairment.

CYP450-Mediated metabolism of suvorexant and investigation of metabolites in forensic case specimens

Suvorexant (Belsomra®) is a sedative hypnotic that was approved for use in 2015. It has a novel mechanism of action and was the first dual orexin receptor antagonist (DORA) to be approved for the treatment of sleep disorders. Sedative hypnotics often feature prominently in forensic investigations such as impaired driving and drug-facilitated sexual assault (DFSA) cases. As such, suvorexant is a drug of interest and its identification in forensic toxicology investigations is of significance. However, limited studies have been published to date and the disposition or importance of its metabolites has been largely uninvestigated. In this report, we investigate the enzymes responsible for metabolism and explore the prevalence of metabolites in blood from a series of thirteen forensic investigations. Recombinant cytochrome P450 enzymes (rCYPs) were used to generate phase I metabolites for suvorexant in vitro, and metabolites were identified using liquid chromatography-quadrupole/time-of-flight-mass spectrometry (LC-Q/TOF-MS). Four rCYP isoenzymes (3A4, 2C19, 2D6, and 2C9) were found to contribute to suvorexant metabolism. The only metabolite identified in blood or plasma arose from hydroxylation of the benzyl triazole moiety (M9). This metabolite was identified in seventeen blood and plasma specimens from twelve medicolegal death investigations and one impaired driving investigation. In the absence of a commercially available reference material, the metabolite was confirmed using rCYP-generated in vitro controls using high resolution mass spectrometry.

Characterization of Five Oxidative Degradation Impurities and One Process Impurity of Suvorexant Drug Substance by LC-MS/MS, HR-MS and 1D, 2D NMR: Validation of Suvorexant Drug Substance and Process Impurities by HPLC and UPLC

During the oxidative (10% H2O2) degradation of suvorexant drug substance, around 1.0% of one impurity and less than 1.0% four impurities were found by a new high-performance liquid chromatography (HPLC) assay and related substance method. The mass numbers of 1.0% impurity was 469 [M + H]+, remaining four impurities were 172 [M + H]+, 467 [M + H]+, 483 [M + H]+ and 485 [M + H]+. The 469 [M + H]+, 485[M + H] and 172 [M + H]+ impurities were characterized by using the LC-MS/MS, HR-MS and 1D, 2D NMR spectroscopic data. The 172 [M + H]+ impurity was prepared synthetically and co-injected in HPLC. The retention time of synthesized 172 [M + H]+ impurity was matching with the unknown degradation impurity in HPLC. The developed mass compatible HPLC and ultra performance liquid chromatography methods were validated for drug substance and process impurities by following ICH Q2 (R1) guidelines.

The Discovery of Suvorexant: Lessons Learned That Can Be Applied to Other CNS Drug Development Efforts

The development of therapeutics for central nervous system (CNS) disorders has many challenges that result in low probability of success and longer-than-typical development timelines. Suvorexant (Belsomra), the first dual orexin receptor antagonist used for insomnia, was approved by the United States Food and Drug Administration ∼10 years after the initial high-throughput screen was conducted to identify orexin receptor antagonists. What accounted for this success and speed? Here we suggest that this program was unique and set up for success by (1) having a robust and high-throughput pharmacodynamic readout that was translatable across species, including humans, (2) a well-validated target with a defined product profile, resulting in a highly energized team with a can-do attitude, and (3) a highly executable and streamlined clinical strategy. The utility of Belsomra for insomnia, as well as other neurological and psychiatric diseases, continues to be explored, most recently for insomnia associated with Alzheimer's disease.

Sleep modulating agents

Sleep and wake are two fundamental states of human existence. Conditions such as insomnia and hypersomnia can have profound negative effects on human health. Many pharmacological interventions impacting sleep and wake are available or are under development. This brief digest surveys early approaches to sleep modulation and highlights recent developments in sleep modulating agents.

Metabolism of the Dual Orexin Receptor Antagonist ACT-541468, Based on Microtracer/ Accelerator Mass Spectrometry

Background:

As part of an integrated and innovative approach to accelerate the clinical development of the dual receptor antagonist ACT-541468, 6 healthy subjects in one cohort in a first-in-humans (FIH) study received an oral dose of 50 mg non-labeled ACT-541468 together with a microtracer amount of 250 nCi of 14C-labeled ACT- 541468 to investigate its absorption, distribution, metabolism, and excretion (ADME).

Methods:

Using accelerator mass spectrometry (AMS), radiochromatograms were constructed for fractionated plasma, urine, and feces samples. Subsequently, the structures of the metabolites were elucidated using high performance liquid chromatography (HPLC) coupled with high resolution mass spectrometry.

Results:

In total 77 metabolites have been identified of which 30, 28, and 60 were present in plasma, urine, and feces, respectively. In plasma, the major metabolites were the mono-oxidized benzylic alcohol M3, the ACT-541468 aldehyde M1, formed by further oxidation of M3 in the benzylic position, and the doubly oxidized M10, formed by (1) benzylic oxidation of M3 (loss of one molecule of water and one molecule of ammonia) and (2) additional loss of water from the oxidized pyrrolidine ring of M5. Transformation of the pyrrolidine to a 6-membered ring was detected. Metabolites that accounted for more than 5% of total radioactivity in excreta were M2, which is also formed by oxidation at the benzylic position, M4, formed by demethylation of the methoxy-group, M7 and A6, both formed by oxidation of M4, and M10, the only major metabolite detected in urine.

Conclusion:

In conclusion, ACT-541468 is extensively metabolized predominantly by oxidative transformations.

Effect of CYP3A Inhibition and Induction on the Pharmacokinetics of Suvorexant: Two Phase I, Open-Label, Fixed-Sequence Trials in Healthy Subjects

BACKGROUND AND OBJECTIVES

Suvorexant is an orexin receptor antagonist indicated for the treatment of insomnia, characterized by difficulties with sleep onset and/or sleep maintenance. As suvorexant is metabolized primarily by Cytochrome P450 3A (CYP3A), and its pharmacokinetics may be affected by CYP3A modulators, the effects of CYP3A inhibitors (ketoconazole or diltiazem) or an inducer (rifampin [rifampicin]) on the pharmacokinetics, safety, and tolerability of suvorexant were investigated.

METHODS

In two Phase I, open-label, fixed-sequence trials (Studies P008 and P038), healthy subjects received a single oral dose of suvorexant followed by co-administration with multiple once-daily doses of strong/moderate CYP3A inhibitors (ketoconazole/diltiazem) or a strong CYP3A inducer (rifampin). Treatments were administered in the morning: suvorexant 4 mg with ketoconazole 400 mg (Study P008; N = 10), suvorexant 20 mg with diltiazem 240 mg (Study P038; N = 20), and suvorexant 40 mg with rifampin 600 mg (Study P038; N = 10). Area under the plasma concentration-time curve from time zero to infinity (AUC_0-∞), maximum plasma concentration (C_max), half-life (t_½), and time to C_max (t_max) were derived from plasma concentrations of suvorexant collected at prespecified time points up to 10 days following CYP3A inhibitor/inducer co-administration. Adverse events (AEs) were recorded.

RESULTS

Co-administration with ketoconazole resulted in increased exposure to suvorexant [AUC_0-∞: geometric mean ratio (GMR); 90% confidence interval (CI) 2.79 (2.35, 3.31)] while co-administration with diltiazem resulted in a lesser effect [GMR (90% CI): 2.05 (1.82, 2.30)]. Co-administration with rifampin led to a marked decrease (88%) in suvorexant exposure. Consistent with morning administration and known suvorexant pharmacology, somnolence was the most frequently reported AE.

CONCLUSIONS

These results are consistent with expectations that strong CYP3A inhibitors and inducers exert marked effects on suvorexant pharmacokinetics. In the context of a limited sample size, single suvorexant doses were generally well tolerated in healthy subjects when co-administered with/without a CYP3A inhibitor/inducer.

Clinical and Experimental Human Sleep-Wake Pharmacogenetics

Sleep and wakefulness are highly complex processes that are elegantly orchestrated by fine-tuned neurochemical changes among neuronal and non-neuronal ensembles, nuclei, and networks of the brain. Important neurotransmitters and neuromodulators regulating the circadian and homeostatic facets of sleep-wake physiology include melatonin, γ-aminobutyric acid, hypocretin, histamine, norepinephrine, serotonin, dopamine, and adenosine. Dysregulation of these neurochemical systems may cause sleep-wake disorders, which are commonly classified into insomnia disorder, parasomnias, circadian rhythm sleep-wake disorders, central disorders of hypersomnolence, sleep-related movement disorders, and sleep-related breathing disorders. Sleep-wake disorders can have far-reaching consequences on physical, mental, and social well-being and health and, thus, need be treated with effective and rational therapies. Apart from behavioral (e.g., cognitive behavioral therapy for insomnia), physiological (e.g., chronotherapy with bright light), and mechanical (e.g., continuous positive airway pressure treatment of obstructive sleep apnea) interventions, pharmacological treatments often are the first-line clinical option to improve disturbed sleep and wake states. Nevertheless, not all patients respond to pharmacotherapy in uniform and beneficial fashion, partly due to genetic differences. The improved understanding of the neurochemical mechanisms regulating sleep and wakefulness and the mode of action of sleep-wake therapeutics has provided a conceptual framework, to search for functional genetic variants modifying individual drug response phenotypes. This article will summarize the currently known genetic polymorphisms that modulate drug sensitivity and exposure, to partly determine individual responses to sleep-wake pharmacotherapy. In addition, a pharmacogenetic strategy will be outlined how based upon classical and opto-/chemogenetic strategies in animals, as well as human genetic associations, circuit mechanisms regulating sleep-wake functions in humans can be identified. As such, experimental human sleep-wake pharmacogenetics forms a bridge spanning basic research and clinical medicine and constitutes an essential step for the search and development of novel sleep-wake targets and therapeutics.

Identification of Suvorexant in Urine Using Liquid Chromatography-Quadrupole/Time-of-Flight Mass Spectrometry (LC-Q/TOF-MS)

Suvorexant (Belsomra®) is a new hypnotic drug with a novel mechanism of action. In prescribed doses of 10 mg before bedtime, the drug produces rapid onset of sleep by inhibiting the orexin neurons of the arousal system, promoting decreased wakefulness. Suvorexant is a potent and highly selective dual orexin receptor antagonist. Sedative hypnotics are of forensic importance due to their widespread use, potential for additive effects with other central nervous system depressants, impairing effects and potential for misuse. In this report we describe a highly sensitive assay for the identification and quantification of suvorexant in urine. Suvorexant was isolated using liquid/liquid extraction (LLE) and identified using liquid chromatography-quadrupole/time-of-flight mass spectrometry. Suvorexant was quantified using a quadratic calibration model between 5 and 250 ng/mL (R2 = 1.000, n = 6). Processed sample stability was demonstrated for up to 24 h. The limit of detection was 0.5 ng/mL and the limit of quantification (LOQ) was 5 ng/mL. The accuracy, bias and precision of the assay at the LOQ were 99% (81-117%), -1% and 12% (n = 18). Intraassay (n = 5) and interassay (n = 15) precision (% CV) at 10, 50 and 200 ng/mL were ≤8%, and bias ranged from -2% to 4% (98-104% accuracy). No qualitative interferences were detected from matrix, internal standard or 50 common drugs. Matrix effects evaluated at low and high concentrations were -16% and -9%, respectively, and produced CVs of 11% and 5% (n = 20). Suvorexant is a new drug of forensic importance. In this report we describe how a simple acidic/neutral LLE can be used to isolate this lipophilic drug with high recoveries and sound analytical performance.

Preclinical assessment of the abuse potential of the orexin receptor antagonist, suvorexant

Suvorexant (Belsomra^®) is a dual orexin receptor antagonist approved for the treatment of insomnia. Because of its pharmacology within the central nervous system, intended therapeutic indication, and first-in-class status, an assessment of suvorexant abuse liability potential was required prior to marketing approval. The nonclinical abuse liability potential studies for suvorexant included: 1) rat drug-dependence model to assess physical dependence following abrupt cessation; 2) rat drug-discrimination model to examine the potential similarity of the interoceptive or subjective effects of suvorexant to those elicited by zolpidem and morphine; 3) self-administration model to assess the relative reinforcing efficacy of suvorexant in rhesus monkeys conditioned to self-administer methohexital. No significant signs of spontaneous drug withdrawal or 'discontinuation syndrome' were observed in rats following abrupt discontinuation of suvorexant. Suvorexant did not elicit complete cross-generalization to either a zolpidem or morphine training/reference stimuli in rats, and suvorexant was devoid of behavioral evidence of positive reinforcing efficacy in monkeys. These nonclinical findings suggested that suvorexant will have low abuse potential in humans. In the final regulatory risk assessment, suvorexant was placed into Schedule IV, likely due to its first-in-class status, its sedative properties, and the outcome of the clinical abuse potential assessment.

Novel class of medications, orexin receptor antagonists, in the treatment of insomnia - critical appraisal of suvorexant

Insomnia, a highly prevalent disorder, can be detrimental to patients' overall health and worsen existing comorbidities. Patients may have acute episodes of insomnia related to a traumatic event, but more commonly insomnia occurs chronically. While proper sleep hygiene and behavioral therapy play important roles in the nonpharmacologic management of short-term and chronic insomnia, medications may also be required. Historically, insomnia has been treated with agents such as benzodiazepines, nonbenzodiazepine receptor agonists, and melatonin agonists. Dual orexin receptor antagonists represent a new class of medications for the treatment of insomnia, which block the binding of wakefulness-promoting neuropeptides orexin A and orexin B to their respective receptor sites. Suvorexant (Belsomra) is the first dual orexin receptor antagonist to be approved in the US and Japan and has demonstrated efficacy in decreasing time to sleep onset and increasing total sleep time. Its unique mechanism of action, data to support efficacy and safety over 12 months of use, and relative lack of withdrawal effects when discontinued may represent an alternative for patients with chronic insomnia who cannot tolerate or do not receive benefit from more traditional sleep agents. Suvorexant is effective and well tolerated, but precautions exist for certain patient populations, including females, obese patients, and those with respiratory disease. Suvorexant has only been studied vs placebo, and hence it is unknown how it directly compares with other medications approved by the US Food and Drug Administration for insomnia. Suvorexant is not likely to replace benzodiazepines or nonbenzodiazepine receptor antagonists as a first-line sleep agent but does represent a novel option for the treatment of patients with chronic insomnia.