Cyanide Trapping of Iminium Ion Reactive Metabolites: Implications for Clinical Hepatotoxicity.

Reactive metabolite formation is a major mechanism of hepatotoxicity. Although reactive electrophiles can be soft or hard in nature, screening strategies have generally focused on the use of glutathione trapping assays to screen for soft electrophiles, with many data sets available to support their use. The use of a similar assay for hard electrophiles using cyanide as the trapping agent is far less common, and there is a lack of studies with sufficient supporting data. Using a set of 260 compounds with a defined hepatotoxicity status by the FDA, a comprehensive literature search yielded cyanide trapping data on an unbalanced set of 20 compounds that were all clinically hepatotoxic. Thus, a further set of 19 compounds was selected to generate cyanide trapping data, resulting in a more balanced data set of 39 compounds. Analysis of the data demonstrated that the cyanide trapping assay had high specificity (92%) and a positive predictive value (83%) such that hepatotoxic compounds would be confidently flagged. Structural analysis of the adducts formed revealed artifactual methylated cyanide adducts to also occur, highlighting the importance of full structural identification to confirm the nature of the adduct formed. The assay was demonstrated to add the most value for compounds containing typical structural alerts for hard electrophile formation: half of the severe hepatotoxins with these structural alerts formed cyanide adducts, while none of the severe hepatotoxins with no relevant structural alerts formed adducts. The assay conditions used included cytosolic enzymes (e.g., aldehyde oxidase) and an optimized cyanide concentration to minimize the inhibition of cytochrome P450 enzymes by cyanide. Based on the demonstrated added value of this assay, it is to be initiated for use at GSK as part of the integrated hepatotoxicity strategy, with its performance being reviewed periodically as more data is generated.

Implementing Tourniquet Conversion Guidelines for Civilian EMS and Prehospital Organizations : A Case Report and Review.

Since the first documented use of a tourniquet in 1674, the popularity of tourniquets has waxed and waned. During recent wars and more recently in Emergency Medical Services systems, the tourniquet has been proven to be a valuable tool in the treatment of life-threatening hemorrhage. However, tourniquet use is not without risk, and several studies have demonstrated adverse events and morbidity associated with tourniquet use in the prehospital setting, particularly when left in place for more than 2 h. Consequently, the US military's Committee on Tactical Combat Casualty Care has recommended guidelines for prehospital tourniquet conversion to reduce the risk of adverse events associated with tourniquets once the initial hemorrhage has been controlled. Emergency Medical Services systems that operate in rural, frontier, and austere environments, especially those with transport times to definitive care that routinely exceed 2 h, may consider implementing similar tourniquet conversion guidelines.

Physiologically Based Pharmacokinetic Modelling of Inhaled Nemiralisib: Mechanistic Components for Pulmonary Absorption, Systemic Distribution, and Oral Absorption.

BACKGROUND AND OBJECTIVES: Physiologically based pharmacokinetic (PBPK) modelling has evolved to accommodate different routes of drug administration and enables prediction of drug concentrations in tissues as well as plasma. The inhalation route of administration has proven successful in treating respiratory diseases but can also be used for rapid systemic delivery, holding great promise for treatment of diseases requiring systemic exposure. The objective of this work was to develop a PBPK model that predicts plasma and tissue concentrations following inhalation administration of the PI3Kδ inhibitor nemiralisib. METHODS: A PBPK model was built in GastroPlus® that includes a complete mechanistic description of pulmonary absorption, systemic distribution and oral absorption following inhalation administration of nemiralisib. The availability of clinical data obtained after intravenous, oral and inhalation administration enabled validation of the model with observed data and accurate assessment of pulmonary drug absorption. The PBPK model described in this study incorporates novel use of key parameters such as lung systemic absorption rate constants derived from human physiological lung blood flows, and implementation of the specific permeability-surface area product per millilitre of tissue cell volume (SpecPStc) to predict tissue distribution. RESULTS: The inhaled PBPK model was verified using plasma and bronchoalveolar lavage fluid concentration data obtained in human subjects. Prediction of tissue concentrations using the permeability-limited systemic disposition tissue model was further validated using tissue concentration data obtained in the rat following intravenous infusion administration to steady state. CONCLUSIONS: Fully mechanistic inhaled PBPK models such as the model described herein could be applied for cross molecule assessments with respect to lung retention and systemic exposure, both in terms of pharmacology and toxicology, and may facilitate clinical indication selection.

Utilising Magnetically Isolated Lysosomes for Direct Quantification of Intralysosomal Drug Concentrations by LC-MS/MS Analysis: An Investigatory Study With Imipramine.

Lysosomes are acidic intracellular organelles that can extensively sequester basic lipophilic drugs due to pH and membrane partitioning, and therefore may significantly influence subcellular drug concentrations. Current in vitro methods for lysosomal drug sequestration evaluation typically lack the ability to accurately and sensitively quantify drug concentrations directly within the lysosome. In the current study, magnetic lysosomal isolation was used in the lysosome rich rat NR8383 cell line and combined with LC-MS/MS analysis to quantify intralysosomal concentrations and lysosomal partitioning (KpLysosome) values of imipramine. The purity of the isolated lysosomes was validated by enzymatic and electron microscopy analysis. Lysosomal imipramine accumulation was explored using 2 methods: addition of imipramine to cells followed by lysosomal isolation (Method 1), and direct addition of imipramine to isolated lysosomes (Method 2). This work highlighted that both experimental buffers and ATP influence intralysosomal drug concentrations, and non-specific drug binding and re-distribution limits the use of Method 1. Method 2 may benefit future lysosomal drug accumulation studies, as imipramine demonstrated high KpLysosome values (3500), comparable to in silico predictions. This study reports a novel method for the direct quantification of intralysosomal drug concentrations that has the ability to be adapted to other cell types.

Effect of tranexamic acid administration time on blood product use in urban trauma patients.

PURPOSE: To evaluate the effect of time to tranexamic acid administration on blood product usage in trauma patients and to assess the potential benefit of initiating a protocol for field administration by ground ambulance personnel. METHODS: Adult patients with traumatic injuries who received 1 g of tranexamic acid during the period January 2014 through June 2016 were retrospectively identified via review of automated dispensing cabinet and electronic medical record data and cross-referencing with the New Mexico Trauma Registry. Exclusion criteria included tranexamic acid use for nontrauma indications, previous admission for trauma during the study period, and a lack of pertinent information regarding the time, type, or severity of trauma in available records. The primary outcome was blood product use (aggregate of units of platelets, packed red blood cells [pRBCs], and fresh frozen plasma [FFP]) in the first 24 hours of hospital admission. RESULTS: The analysis included 107 patient cases, with a median transport time of 20 minutes (range, 7-103 minutes); 73% of reported transport times were less than 30 minutes. All patients received a loading dose of tranexamic acid in the hospital, with the exception of 2 patients who received tranexamic acid in the field. Administration of a tranexamic acid loading dose was documented within 3 hours for 90.7% of patients, with a mean time to administration of 91.9 minutes. A mean (SD) total of 14.8 (16.0) units of blood products (range, 0-91 units) were administered, consisting of a mean (SD) of 8.0 (8.4) units of pRBCs (range, 0-48 units), 5.6 (7.5) units of FFP (range, 0-38 units), and 1.2 (1.7) units of platelets (range, 0-7 units). Time to tranexamic acid administration did not affect blood product usage in the first 24 hours of admission after adjusting for potential confounders. CONCLUSION: Earlier administration of tranexamic acid was not associated with a decrease in use of blood products. This finding, paired with the relatively short ground transport times typical for our institution, makes it unlikely that field administration of tranexamic acid would benefit the evaluated patient population.

A Novel Inhaled Dry-Powder Formulation of Ribavirin Allows for Efficient Lung Delivery in Healthy Participants and Those with Chronic Obstructive Pulmonary Disease in a Phase 1 Study.

Chronic obstructive pulmonary disease (COPD) is an inflammatory lung condition, causing progressive decline in lung function leading to premature death. Acute exacerbations in COPD patients are predominantly associated with respiratory viruses. Ribavirin is a generic broad-spectrum antiviral agent that could be used for treatment of viral respiratory infections in COPD. Using the Particle Replication In Nonwetting Templates (PRINT) technology, which produces dry-powder particles of uniform shape and size, two new inhaled formulations of ribavirin (ribavirin-PRINT-CFI and ribavirin-PRINT-IP) were developed for efficient delivery to the lung and to minimize bystander exposure. Ribavirin-PRINT-CFI was well tolerated in healthy participants after single dosing and ribavirin-PRINT-IP was well tolerated in healthy and COPD participants after single and repeat dosing. Ribavirin-PRINT-CFI was replaced with ribavirin-PRINT-IP since the latter formulation was found to have improved physicochemical properties and it had a higher ratio of active drug to excipient per unit dose. Ribavirin concentrations were measured in lung epithelial lining fluid in both healthy and COPD participants and achieved target concentrations. Both formulations were rapidly absorbed with approximately dose proportional pharmacokinetics in plasma. Exposure to bystanders was negligible based on both the plasma and airborne ribavirin concentrations with the ribavirin-PRINT-IP formulation. Thus, ribavirin-PRINT-IP allowed for an efficient and convenient delivery of ribavirin to the lungs while minimizing systemic exposure. Further clinical investigations would be required to demonstrate ribavirin-PRINT-IP antiviral characteristics and impact on COPD viral-induced exacerbations. (The clinical trials discussed in this study have been registered at ClinicalTrials.gov under identifiers NCT03243760 and NCT03235726.).

Drug Interactions for Low-Dose Inhaled Nemiralisib: A Case Study Integrating Modeling, In Vitro, and Clinical Investigations.

In vitro data for low-dose inhaled phosphoinositide 3-kinase delta inhibitor nemiralisib revealed that it was a substrate and a potent metabolism-dependent inhibitor of cytochrome P450 (P450) 3A4 and a P-glycoprotein (P-gp) substrate. An integrated in silico, in vitro, and clinical approach including a clinical drug interaction study as well as a bespoke physiologically based pharmacokinetic (PBPK) model was used to assess the drug-drug interaction (DDI) risk. Inhaled nemiralisib (100 µg, single dose) was coadministered with itraconazole, a potent P4503A4/P-gp inhibitor, following 200 mg daily administrations for 10 days in 20 male healthy subjects. Systemic exposure to nemiralisib (AUC0-inf) increased by 2.01-fold versus nemiralisib alone. To extrapolate the clinical data to other P4503A4 inhibitors, an inhaled PBPK model was developed using Simcyp software. Retrospective simulation of the victim risk showed good agreement between simulated and observed data (AUC0-inf ratio 2.3 vs. 2.01, respectively). Prospective DDI simulations predicted a weak but manageable drug interaction when nemiralisib was coadministered with other P4503A4 inhibitors, such as the macrolides clarithromycin and erythromycin (simulated AUC0-inf ratio of 1.7), both common comedications in the intended patient populations. PBPK and static mechanistic models were also used to predict a negligible perpetrator DDI effect for nemiralisib on other P4503A4 substrates, including midazolam (a sensitive probe substrate of P4503A4) and theophylline (a narrow therapeutic index drug and another common comedication). In summary, an integrated in silico, in vitro, and clinical approach including an inhalation PBPK model has successfully discharged any potential patient DDI risks in future nemiralisib clinical trials. SIGNIFICANCE STATEMENT: This paper describes the integration of in silico, in vitro, and clinical data to successfully discharge potential drug-drug interaction risks for a low-dose inhaled drug. This work featured assessment of victim and perpetrator risks of drug transporters and cytochrome P450 enzymes, utilizing empirical and mechanistic approaches combined with clinical data (drug interaction and human absorption, metabolism, and pharmacokinetics) and physiologically based pharmacokinetic modeling approaches to facilitate bespoke risk assessment in target patient populations.

An Innovative Approach to Characterize Clinical ADME and Pharmacokinetics of the Inhaled Drug Nemiralisib Using an Intravenous Microtracer Combined with an Inhaled Dose and an Oral Radiolabel Dose in Healthy Male Subjects.

An innovative open-label, crossover clinical study was used to investigate the excretion balance, pharmacokinetics, and metabolism of nemiralisib-an inhaled phosphoinositide 3-kinase delta inhibitor being developed for respiratory diseases. Six healthy men received a single intravenous microtracer of 10 µg [14C]nemiralisib with a concomitant inhaled nonradiolabeled 1000 µg dose followed by an oral 800 µg dose of [14C]nemiralisib 14 days later. Complementary methods including accelerator mass spectrometry allowed characterization of a range of parameters including oral absorption (Fabs), proportion of nemiralisib escaping gut wall metabolism (Fg), hepatic extraction (Eh), fraction of dose absorbed from inhaled dose (Flung), and renal clearance. Intravenous pharmacokinetics of nemiralisib were characterized by low blood clearance (10.0 l/h), long terminal half-life (55 hours), and high volume of distribution at steady state (728 l). Nemiralisib exhibited moderate inhaled and oral bioavailability (38% and 35%) while Flung was 29%. Absorption and first-pass parameters were corrected for blood renal clearance and compared with values without correction. Any swallowed nemiralisib was relatively well absorbed (Fabs, 0.48) with a high fraction escaping gut wall metabolism and low extraction by the liver (Fg and Eh being 0.83 and 0.10, respectively). There were no major human plasma metabolites requiring further qualification in animal studies. Both unchanged nemiralisib and its oxidative/conjugative metabolites were secreted in bile, with nemiralisib likely subject to further metabolism through enterohepatic recirculation. Direct renal clearance and metabolism followed by renal clearance were lesser routes of elimination. SIGNIFICANCE STATEMENT: A number of innovative features have been combined into one small clinical study enabling a comprehensive description of the human pharmacokinetics and metabolism of an inhaled molecule. Design elements included an intravenous 14C tracer administration concomitant with an inhalation dose that enabled derivation of parameters such as fraction absorbed (Fabs), the proportion of drug escaping first-pass extraction through the gut wall and liver (Fg and Fh) and hepatic extraction (Eh). Entero-test bile sampling enabled characterization of biliary elimination pathways.

Translation of Inhaled Drug Optimization Strategies into Clinical Pharmacokinetics and Pharmacodynamics Using GSK2292767A, a Novel Inhaled Phosphoinositide 3-Kinase δ Inhibitor.

This study describes the pharmacokinetic (PK) and pharmaco-dynamic (PD) profile of N-(5-(4-(5-(((2R,6S)-2,6-dimethylmorpholino)methyl)oxazol-2-yl)-1H-indazol-6-yl)-2-methoxypyridin-3-yl)methanesulfonamide (GSK2292767A), a novel low-solubility inhaled phosphoinositide 3-kinase delta (PI3Kδ) inhibitor developed as an alternative to 2-(6-(1H-indol-4-yl)-1H-indazol-4-yl)-5-((4-isopropylpiperazin-1-yl)methyl)oxazole (nemiralisib), which is a highly soluble inhaled inhibitor of PI3Kδ with a lung profile consistent with once-daily dosing. GSK2292767A has a similar in vitro cellular profile to nemiralisib and reduces eosinophilia in a murine PD model by 63% (n = 5, P < 0.05). To explore whether a low-soluble compound results in effective PI3Kδ inhibition in humans, a first time in human study was conducted with GSK2292767A in healthy volunteers who smoke. GSK2292767A was generally well tolerated, with headache being the most common reported adverse event. PD changes in induced sputum were measured in combination with drug concentrations in plasma from single (0.05-2 mg, n = 37), and 14-day repeat (2 mg, n = 12) doses of GSK2292767A. Trough bronchoalveolar lavage (BAL) for PK was taken after 14 days of repeat dosing. GSK2292767A displayed a linear increase in plasma exposure with dose, with marginal accumulation after 14 days. Induced sputum showed a 27% (90% confidence interval 15%, 37%) reduction in phosphatidylinositol-trisphosphate (the product of phosphoinositide 3-kinase activation) 3 hours after a single dose. Reduction was not maintained 24 hours after single or repeat dosing. BAL analysis confirmed the presence of GSK2292767A in lung at 24 hours, consistent with the preclinical lung retention profile. Despite good lung retention, target engagement was only present at 3 hours. This exposure-response disconnect is an important observation for future inhaled drug design strategies considering low solubility to drive lung retention.

Observational Study of Grand Canyon Rim-to-Rim Day Hikers: Determining Behavior Patterns to Aid in Preventive Search and Rescue Efforts.

INTRODUCTION: Grand Canyon National Park has seen an increase in visitors traversing the canyon from rim to rim (R2R) in a single day. R2R hikers travel over 33.8 km (21 mi) over 3300 m (11,000 ft) of elevation change and endure large temperature changes. Grand Canyon emergency medical service providers provide emergency medical services to over 1100 visitors annually. Direct guidance by Preventive Search and Rescue rangers has improved safety. The objective of this study was to examine visitors attempting an R2R traverse and to enhance PSAR rangers' anticipatory guidance. METHODS: We conducted an observational study of R2R hikers in the spring and fall of 2015. Hikers consented to study inclusion and were interviewed at the starting trailhead, canyon bottom, and exit trailhead. We performed a survey and collected biometric data. RESULTS: We enrolled 617 visitors with a median age of 43 y (interquartile range [IQR] 33-53); 65% were male and 46% had hiked the R2R a median number of 3 times previously (IQR 2-7). Hydration strategies included water bottle only (20%), hydration bladder only (31%), and both water bottle and hydration bladder (48%). R2R crossers had an average start time of 0530 (SD 1.3 h) and median crossing time of 11.9 h (IQR 10.7-13.3). Crossing time and self-reported fatigue were negatively correlated with prior R2R experience (P=0.02). CONCLUSIONS: Crossing R2R in a day is hazardous and associated with risk of injury and illness. The results of this study can be used by Preventive Search and Rescue to reduce these risks by educating hikers.

Observational Multicenter Study of a Direct-to-CT Protocol for EMS-transported Patients with Suspected Stroke.

OBJECTIVE: In an effort to decrease door-to-needle times for patients with acute ischemic stroke, some hospitals have begun taking stable EMS patients with suspected stroke directly from the ambulance to the CT scanner, then to an emergency department (ED) bed for evaluation. Minimal data exist regarding the potential for time savings with such a protocol. The study hypothesis was that a direct-to-CT protocol would be associated with decreases in both door-to-CT-ordered and door-to-needle times. METHODS: An observational, multicenter before/after study was conducted of time/process measures at hospitals that have implemented direct-to-CT protocols for patients transported by EMS with suspected stroke. Participating hospitals submitted data on at least the last 50 "EMS stroke alert" patients before the launch of the direct-to-CT protocol, and at least the first 50 patients after. Time elements studied were arrival at the ED, time the head CT was ordered, and time tPA was started. Data were submitted in blinded fashion (patient and hospital identifiers removed); at the time of data analysis, the lead investigator was unaware of which data came from which hospital. Simple descriptive statistics were used, along with the Mann-Whitney test to compare time medians. RESULTS: Seven hospitals contributed data on 1040 patients (529 "before" and 511 "after"); 512 were male, and 627 had final diagnoses of ischemic stroke, of whom 275 received tPA. The median door-to-CT-ordered time for all patients was 7 minutes in the before phase, and 4 minutes after (difference 3 minutes, p = < 0.0001); similarly, the median door-to-CT-started time was 6 minutes "before" and 10 minutes after (p < 0.0001). The median door-to-needle time for all patients given tPA was 42 minutes before, and 44 minutes after (p = 0.78). Four hospitals had modest decreases in door-to-CT-ordered time (of 2, 4, 2, and 5 minutes), and only one hospital had a decrease in door-to-needle time (32 min vs 26 min, p = 0.012). CONCLUSIONS: In this sample from seven hospitals, a minimal reduction in door-to-CT-ordered and door-to-CT-started time, but no change in door-to-needle time, was found for EMS patients with suspected stroke taken directly to the CT scanner, compared to those evaluated in the ED prior to CT.

Multi-Patient Rabies Exposure on a Colorado River Rafting Expedition: Urgent vs. Emergent Transport Decision Making in an Austere Setting.

We present a case of rabies exposure on a private river rafting trip on Grand Canyon National Park's Colorado River. Five individuals were exposed to an erratically acting bat; one of the individuals sustained a direct bite to the upper lip while sleeping. This case illustrates the challenges of austere medical care and evacuation in remote conditions while highlighting the importance of risk mitigation considerations in all austere situations.

Interrogating the relationship between rat in vivo tissue distribution and drug property data for >200 structurally unrelated molecules.

The ability to explain distribution patterns from drug physicochemical properties and binding characteristics has been explored for more than 200 compounds by interrogating data from quantitative whole body autoradiography studies (QWBA). These in vivo outcomes have been compared to in silico and in vitro drug property data to determine the most influential properties governing drug distribution. Consistent with current knowledge, in vivo distribution was most influenced by ionization state and lipophilicity which in turn affected phospholipid and plasma protein binding. Basic and neutral molecules were generally better distributed than acidic counterparts demonstrating weaker plasma protein and stronger phospholipid binding. The influence of phospholipid binding was particularly evident in tissues with high phospholipid content like spleen and lung. Conversely, poorer distribution of acidic drugs was associated with stronger plasma protein and weaker phospholipid binding. The distribution of a proportion of acidic drugs was enhanced, however, in tissues known to express anionic uptake transporters such as the liver and kidney. Greatest distribution was observed into melanin containing tissues of the eye, most likely due to melanin binding. Basic molecules were consistently better distributed into parts of the eye and skin containing melanin than those without. The data, therefore, suggest that drug binding to macromolecules strongly influences the distribution of total drug for a large proportion of molecules in most tissues. Reducing lipophilicity, a strategy often used in discovery to optimize pharmacokinetic properties such as absorption and clearance, also decreased the influence of nonspecific binding on drug distribution.

Development of a novel remote-controlled and self-contained audiovisual-aided interactive system for immobilizing claustrophobic patients.

In radiotherapy, only a few immobilization systems, such as open-face mask and head mold with a bite plate, are available for claustrophobic patients with a certain degree of discomfort. The purpose of this study was to develop a remote-controlled and self-contained audiovisual (AV)-aided interactive system with the iPad mini with Retina display for intrafractional motion management in brain/H&N (head and neck) radiotherapy for claustrophobic patients. The self-contained, AV-aided interactive system utilized two tablet computers: one for AV-aided interactive guidance for the subject and the other for remote control by an operator. The tablet for audiovisual guidance traced the motion of a colored marker using the built-in front-facing camera, and the remote control tablet at the control room used infrastructure Wi-Fi networks for real-time communication with the other tablet. In the evaluation, a programmed QUASAR motion phantom was used to test the temporal and positional accuracy and resolution. Position data were also obtained from ten healthy volunteers with and without guidance to evaluate the reduction of intrafractional head motion in simulations of a claustrophobic brain or H&N case. In the phantom study, the temporal and positional resolution was 24 Hz and 0.2 mm. In the volunteer study, the average superior-inferior and right-left displacement was reduced from 1.9 mm to 0.3 mm and from 2.2 mm to 0.2 mm with AV-aided interactive guidance, respectively. The superior-inferior and right-left positional drift was reduced from 0.5 mm/min to 0.1 mm/min and from 0.4 mm/min to 0.04 mm/min with audiovisual-aided interactive guidance. This study demonstrated a reduction in intrafractional head motion using a remote-controlled and self-contained AV-aided interactive system of iPad minis with Retina display, easily obtainable and cost-effective tablet computers. This approach can potentially streamline clinical flow for claustrophobic patients without a head mask and also allows patients to practice self-motion management before radiation treatment delivery.

Disaster mitigation: initial response.

The objective of this review is to stimulate the reader's considerations for developing community disaster mitigation. Disaster mitigation begins long before impact and is defined as the actions taken by a community to eliminate or minimize the impact of a disaster. The assessment of vulnerabilities, the development of infrastructure, memoranda of understanding, and planning for a sustainable response and recovery are parts of the process. Empowering leadership and citizens with knowledge of available resources through the planning and development of a disaster response can strengthen a community's resilience, which can only add to the viability and quality of life enjoyed by the entire community.

Metabolism and disposition of vilanterol, a long-acting ß(2)-adrenoceptor agonist for inhalation use in humans.

The metabolism and disposition of vilanterol, a novel long-acting ß(2)-adrenoceptor agonist (LABA) for inhalation use, was investigated after oral administration in humans. Single oral administrations of up to 500 µg of vilanterol were shown to be safe and well tolerated in two clinical studies in healthy men. In a human radiolabel study, six healthy men received a single oral dose of 200 µg of [(14)C]vilanterol (74 kBq). Plasma, urine, and feces were collected up to 168 hours after the dose and were analyzed for vilanterol, metabolites, and radioactivity. At least 50% of the radioactive dose was orally absorbed. The primary route of excretion of drug-related material was via O-dealkylation to metabolites, which were mainly excreted in urine. Vilanterol represented a very small percentage (<0.5%) of the total drug-related material in plasma, indicative of extensive first-pass metabolism. Circulating metabolites resulted mainly from O-dealkylation and exhibited negligible pharmacologic activity. The therapeutic dose level for vilanterol is 25 µg by the inhalation route. At this low-dose level, the likelihood of pharmacologically inactive metabolites causing unexpected toxicity is negligible. In addition to providing an assessment of the disposition of vilanterol in human, this work highlights a number of complexities associated with determining human absorption, distribution, metabolism, and excretion (ADME) for inhaled molecules--mainly related to the low chemical doses and complications associated with the inhalation route of administration.

Preclinical strategy to reduce clinical hepatotoxicity using in vitro bioactivation data for >200 compounds.

Drug-induced liver injury is the most common cause of market withdrawal of pharmaceuticals, and thus, there is considerable need for better prediction models for DILI early in drug discovery. We present a study involving 223 marketed drugs (51% associated with clinical hepatotoxicity; 49% non-hepatotoxic) to assess the concordance of in vitro bioactivation data with clinical hepatotoxicity and have used these data to develop a decision tree to help reduce late-stage candidate attrition. Data to assess P450 metabolism-dependent inhibition (MDI) for all common drug-metabolizing P450 enzymes were generated for 179 of these compounds, GSH adduct data generated for 190 compounds, covalent binding data obtained for 53 compounds, and clinical dose data obtained for all compounds. Individual data for all 223 compounds are presented here and interrogated to determine what level of an alert to consider termination of a compound. The analysis showed that 76% of drugs with a daily dose of <100 mg were non-hepatotoxic (p < 0.0001). Drugs with a daily dose of ≥100 mg or with GSH adduct formation, marked P450 MDI, or covalent binding ≥200 pmol eq/mg protein tended to be hepatotoxic (∼ 65% in each case). Combining dose with each bioactivation assay increased this association significantly (80-100%, p < 0.0001). These analyses were then used to develop the decision tree and the tree tested using 196 of the compounds with sufficient data (49% hepatotoxic; 51% non-hepatotoxic). The results of these outcome analyses demonstrated the utility of the tree in selectively terminating hepatotoxic compounds early; 45% of the hepatotoxic compounds evaluated using the tree were recommended for termination before candidate selection, whereas only 10% of the non-hepatotoxic compounds were recommended for termination. An independent set of 10 GSK compounds with known clinical hepatotoxicity status were also assessed using the tree, with similar results.

An integrated reactive metabolite evaluation approach to assess and reduce safety risk during drug discovery and development.

Metabolic bioactivation is widely considered an undesirable event and a likely prerequisite step in the expression of drug-induced hepatotoxicity and hypersensitivity. Reducing bioactivation risk early in drug discovery, therefore, may help reduce compound attrition and provide safer drug therapies. In vitro bioactivation data and clinical dose for a large set of marketed drugs were analysed for their concordance with clinical hepatotoxicity and the data used to develop an early reactive metabolite strategy. A contingency table analysis of cytochrome P450 metabolism-dependent inhibition (CYP MDI), glutathione trapping data, and dose for >200 marketed drugs with or without a clinical hepatotoxic signal; and microsomal covalent binding data and dose for ∼60 marketed compounds obtained from literature publications was performed to assess concordance with hepatotoxicity. Clinical daily dose ≥100mg or glutathione adduct formation was strongly associated with hepatotoxicity (p<0.0001, p=0.003, respectively). A trend towards clinical hepatotoxicity was observed with marked CYP MDI or metabolism-dependent covalent binding ≥200pmol/mg. The percentage of hepatotoxic drugs identified by high dose (67%) increased significantly when bioactivation data were combined with dose (80-100%). As CYP MDI and glutathione adduct assays do not require the synthesis of radiolabelled compound and are relatively easy to conduct, they may be of particular value for early assessment in programs with lower risk tolerance. Such information together with an overall understanding of the metabolic properties of the compound and risk/benefit considerations may trigger further assessment. Additionally hepatic transcriptomic data (e.g., Nrf2-activated gene expression) from rat toxicity studies can provide evidence of in vivo consequences of bioactivation. As attenuation of a metabolic bioactivation risk early in drug discovery could reduce compound attrition and provide safer drug therapies, we have developed a decision-based early reactive metabolite strategy that can be tailored to the needs of individual programs.