Acute block of hERG channels is the most common mechanism underlying drug-induced QTC prolongation and potentially fatal Torsade de Pointes arrhythmia. Updates to ICH E14 Q&As now allow for using negative nonclinical data, including hERG, to support QTC risk assessment in late-stage clinical development. To interpret the hERG results, understanding hERG assay reproducibility or hERG data variability is pivotal. Protocol and best practice recommendations have been provided with the goal of minimizing lab-to-lab data differences, but the impact remains unclear. To fill this knowledge gap, hERG data from a HESI-coordinated multi-laboratory study were leveraged. Using standardized protocol and following best practices for patch clamp studies, five laboratories tested 28 drugs using the manual patch clamp technique. Systematic differences in block potencies were observed for data generated by one laboratory for the first 21 drugs, and these differences disappeared for the last seven drugs. Exposure, pharmacological sensitivity of the cell lines, and cell/data qualities were ruled out as the factors underlying systematic differences. All laboratories retested two drugs and obtained results within 1.6X of the initial testings, except for another laboratory that obtained data for one drug that differed from its initial testing by 7.6X. Descriptive statistics and meta-analysis were applied to the dataset to estimate what the distribution in hERG block potencies would be if a laboratory were to test the same drug repeatedly. This measure, or hERG data variability, was ~ 5X. Based on these results, hERG block potency values within 5X of each other should not be considered different, since these values are within the natural data distribution of the hERG assay; laboratory-specific safety margin threshold may be required to account for systematic data differences.

The removal of hemp from the definition of marijuana in the 2018 Agricultural Improvement Act has increased the number of cannabidiol-containing products available to consumers. Consequently, consumer use has also increased. Increased product availability and use drives the need for sensitive and specific analytical assays to measure the cannabidiol (CBD) and metabolites in patients, to establish dose-effect relationships and to gain knowledge of their pharmacokinetics. Here we describe the development and validation of a rapid high-throughput LC-MS/MS bioanalytical method for the quantification of cannabidiol and primary metabolites in human plasma to support an FDA-sponsored clinical study (NCT06192589). Sample preparation a single step protein precipitation followed by filtration through 96-well Phree™ Phospholipid removal plates. The method was validated over ranges of CBD: 1.95-500.00 ng mL-1; 7-hydroxy-cannabidiol (7-OH-CBD): 3.91-1000.00 ng mL-1; 7-carboxy-cannabidiol (7-COOH-CBD): 31.25-8000.00 ng mL-1. There was no cross-analyte interference, injection carryover, or matrix effect observed with this method. Analyte recoveries were consistent across three QC levels ranging from 83.90 to 90.85 %. Inter-day Accuracy across four QC level of all three analytes ranged from 93.87 to 107.31 % while precision ranged from 1.03 to 14.33 %. These results and other outlined in this manuscript met acceptance criteria as outline the current M10 Guidance for Bioanalytical Method Validation and Study Sample Analysis.

The most common mechanism of drug-induced QTC prolongation and the potentially fatal arrhythmia Torsade de Pointes is block of hERG channels. Accordingly, the hERG assay is used to assess cardiac safety of new drugs in support of first-in-human studies. The recently updated ICH E14 Q&As 5.1 and 6.1 describe regulatory pathways to use hERG results obtained following best practice recommendations (ICH S7B Q&A 2.1) to complement clinical QTC data that otherwise may not be adequate and inform labeling. However, the impact of protocol standardization on variability of hERG data has not been assessed. This is a critical data gap in implementation of the E14/S7B Q&As. This hERG dataset was collected as part of a HESI-coordinated international effort designed to generate cardiac ion channel data using physiologically relevant protocols when feasible and practical, following best practice recommendations in ICH S7B Q&As. Datasets for other cardiac ion channels are presented in a companion abstract (Yu et al.). Five laboratories established drug block potencies (IC50s) for 28 clinical drugs in a two-phase study using manual patch clamp. Concentration verification was done to assess drug losses for all laboratories and drugs. Meta-analysis was used to estimate overall variability in IC50s. Phase 1 study showed that hERG IC50s were similar for four laboratories and systematically higher for one laboratory. The source of the systematic difference could not be identified and was not attributed to different extent of drug loss, drug delivery method, cell lines, or recording quality. The systematic difference disappeared during phase 2. Blind repeat testing of two phase 1 drugs was done by each laboratory to understand within the laboratory reproducibility. The overall variability (or reproducibility) of the hERG assay was estimated accounting for potency differences among different drugs and laboratory-specific tendencies. This variability indicates the resolution limit of the hERG assay under best practices to distinguish two IC50s as different. Systematic differences in hERG IC50s can occur following protocol standardization and ICH S7B best practice recommendations. The regulatory framework for identifying hERG-positive molecules should account for hERG data variability and may additionally need to account for laboratory-specific differences.

BackgroundThere is a need to reliably predict the permeability of inhaled compounds during the development of new and generic drugs. A small airway microphysiological system (MPS) that can recapitulate the pulmonary air-liquid interface (ALI) with primary epithelial and vascular endothelial cell layers may provide a more physiologically relevant environment for measuring drug permeability than simpler two-dimensional in vitro cell culture platforms. Therefore, we evaluated the use of a small airway MPS to measure the permeability of inhaled drugs.MethodologyPrimary human lung epithelial cells were seeded onto the top channel of the chip and cultured for 14 days at ALI to promote monolayer differentiation, followed by addition of endothelial cells into the bottom channel. Due to the non-specific binding properties of polydimethylsiloxane (PDMS), a drug absorption study was conducted to quantify non-specific binding to the material. Drug permeability was evaluated by passing each compound (10 µM) through the top channel and measuring the amount of drug that permeated into the bottom channel over the time course of 30, 60, 120, and 180 min.ResultsConfocal micrographs demonstrated the presence of tight junctions along with basal, goblet, and ciliated cells in the top channel and attachment of endothelial cells in the bottom channel. Insignificant nonspecific binding to the MPS was observed with albuterol sulfate, formoterol fumarate, and olodaterol hydrochloride (HCl), while fluticasone furoate showed significant nonspecific binding as only 6%–44% of the drug was recovered at 30 and 120 min, respectively. As a result, fluticasone furoate was excluded from further analysis. Permeability studies estimated an apparent permeability (Papp) of 1.02 × 10−6 cm/s for albuterol sulfate, 0.0813 × 10−6 cm/s for olodaterol HCl, and 2.44 × 10−6 cm/s for formoterol fumarate.DiscussionTaken together, the small airway MPS recapitulated relevant cell types and many morphological features in the lung. The apparent permeabilities measured indicated that albuterol sulfate and formoterol fumarate would be categorized as highly permeable, while olodaterol HCl would be categorized as a low permeable drug.

Pharmacodynamic (PD) biomarkers can support biosimilarity assessment, potentially reducing the need for comparative clinical efficacy studies. This study aimed to characterize previously identified proteomic PD biomarker candidates for Interferon beta-1a (IFNβ-1a, n = 248) and pegylated IFNβ-1a (pegIFNβ-1a, n = 528) biologics at therapeutic doses, to further evaluate the utility of proteomics in biosimilar development. Here, we reproduced the results at lower doses and characterized PD responses across multiple doses using criteria for justifying PD biomarker use in biosimilar development. We analyzed candidate proteins from longitudinal proteomics data (SomaScan™ Assay v4.1) from 48 healthy subjects administered intermediate or low doses of IFNβ-1a (15, 7.5 μg) or pegIFNβ-1a (62.5, 31.25 μg) in an FDA-sponsored study, alongside previously published therapeutic dose and placebo data. EDTA plasma samples were collected at 0, 0.125, 0.33, 0.67, 1.33, 2, 3, 4, 5, 6 days and at 9, 13 days additionally for pegIFNβ-1a. Prioritization criteria included significant differential expression at the intermediate dose vs. placebo, ≥20% response difference from placebo, significant baseline-adjusted area under the effect curve (AUEC) and a monotonic dose-response relationship across all doses. Among the candidates, 165 and 323 were differentially expressed at intermediate doses of IFNβ-1a and pegIFNβ-1a respectively. Nine PD biomarkers, including C-X-C motif chemokine 11 (I-TAC), Lymphocyte activation gene 3 protein (LAG3), and Granulins (GRN), were prioritized as common to both biologics. Most candidates followed the Emax dose-response model. I-TAC showed the strongest response, and LAG-3 showed the least variability in AUEC. Our study identified several suitable plasma PD biomarkers for IFNβ-1a and pegIFNβ-1a biologics with potential utility in biosimilar development programs.

Current in vitro cell-based methods, relying on single cell types, have structural and functional limitations in determining lung drug permeability, which is a contributing factor affecting both local and systemic drug levels. To address this issue, we investigated a 3D human lung airway model generated using a cell culture insert, wherein primary human lung epithelial and endothelial cells were cocultured at an air-liquid interface (ALI). To ensure that the cell culture mimics the physiological and functional characteristics of airway tissue, the model was characterized by evaluating several parameters such as cellular confluency, ciliation, tight junctions, mucus-layer formation, transepithelial electrical resistance, and barrier function through assaying fluorescein isothiocyanate-dextran permeability. To understand how the characterized ALI quality attributes influenced the absorption of inhaled drugs through the epithelial-endothelial barrier, we measured the permeability and epithelial intracellular concentrations of albuterol sulfate (AL), formoterol fumarate (FO), and fluticasone furoate (FL). The presented characterization results overall demonstrate that this culture platform mimicked the airway-specific structure and barrier function. An apparent permeability (P app) of 5.7 × 10-6 cm/s and an intracellular concentration below 1% were quantified for AL over 3 h. The P app of FO was 8.5 × 10-6 cm/s, with an intracellular concentration of 3.8%. Due to its high lipophilicity, FL showed a higher intracellular concentration (17.4%) compared to AL and FO, but also a 73.1% loss of the compound over 3 h due to nonspecific binding, with a P app as low as 1.3 × 10-7 cm/s. While the model exhibited physiologically relevant properties, its utility in estimating the permeability of inhaled drugs may be drug-specific, warranting further optimization and study.

Tacrolimus capsules contain the drug as the amorphous form. It is well known that drug crystallinity is a risk factor for the performance of amorphous formulations. This study investigated the impact of varying levels of crystalline drug on the pharmacokinetics of tacrolimus following oral dosing of a 5 mg capsule under fasting conditions. Two treatments with percent crystallinity of 20% and 50% were achieved by exposing a marketed generic tacrolimus product to open dish storage conditions of 35 °C and 75% relative humidity (RH) for up to 20 days. Crystallinity was monitored with X-ray powder diffraction. Prograf®, the reference listed drug (RLD), an amorphous generic drug product, and generic drug products containing 20% and 50% crystalline tacrolimus were evaluated. All four treatments were administered to healthy participants in a randomized, single-dose, four-treatment, four-period, four-way crossover study. Blood sampling occurred over 24 h. The amorphous generic tacrolimus product was determined not to be bioequivalent to the RLD. The capsules containing both 20% and 50% crystalline tacrolimus also failed the bioequivalence recommendations when compared to the amorphous generic or to the RLD. Both levels of crystalline tacrolimus resulted in BE failure for both Cmax and AUC parameters. The impact of tacrolimus crystallization was greater for maximum blood concentration (Cmax) values relative to the area-under-the-curve (AUC) values. This study demonstrates that crystalline tacrolimus formed in a marketed generic product and these changes resulted in variable pharmacokinetics which could be of significant clinical concern.

Endogenous therapeutic analytes include hormones, neurotransmitters, vitamins, fatty acids and inorganic elements that are naturally present in the body because either the body produces them or they are present in the normal diet. The accurate measurement of endogenous therapeutic analytes poses a challenge when the administered exogenous therapeutic analyte and its endogenous counterpart cannot be distinguished. In this article, real case examples with endogenous therapeutic analyte bioanalysis during drug development in support of regulatory submissions are collected and presented. The article highlights common challenges encountered and lessons learned related to bioanalysis of endogenous therapeutic analytes and provides practical tips and strategies to consider from a regulatory perspective.

The US Food and Drug Administration (FDA) guidance describes how pharmacodynamic (PD) biomarkers can be used to address residual uncertainty and demonstrate no clinically meaningful differences between a proposed biosimilar and its reference product without relying on clinical efficacy end point(s). Pilot studies and modeling can inform dosing for such PD studies. To that end, we conducted a randomized, double-blinded, placebo-controlled, single-dose, parallel-arm clinical study in healthy participants to evaluate approaches to address information gaps, inform best practices for analysis of biomarker samples and study results, and apply emerging technologies in biomarker characterization. Seventy-two healthy participants (n = 8 per arm) received either placebo or 1 of 4 doses of the interleukin-5 inhibitors mepolizumab (3-24 mg) or reslizumab (0.1-0.8 mg/kg). A clinical study using doses lower than approved therapeutic doses was combined with modeling and simulation to evaluate the dose-response relationship of the biomarker eosinophils. There was no dose-response relationship for eosinophil counts due to variability, although the mepolizumab 24 mg and reslizumab 0.8 mg/kg doses showed clear effects. Published indirect-response models were used to explore eosinophil data across doses from this study and the unstudied therapeutic doses. Simulations were used to calculate typical PD metrics, such as baseline-adjusted area under the effect curve and maximum change from baseline. The simulation results demonstrate sensitivity of eosinophils as a PD biomarker and indicate doses lower than the approved doses would have PD responses overlapping with variability in the placebo arm. The simulation results further highlight the utility of model-based approaches in supporting use of PD biomarkers in biosimilar development.

Control of N-nitrosoamine impurities is important for ensuring the safety of drug products. Findings of nitrosamine impurities in some drug products led FDA to develop new guidance providing recommendations for manufacturers towards prevention and detection of nitrosamine impurities in pharmaceutical products. One of these products, ranitidine, also had a published in vivo study, which has since been retracted by its authors, suggesting a potential for in vivo conversion of ranitidine to the probable human carcinogen, N-nitrosodimethylamine (NDMA). FDA subsequently initiated a randomized, double-blind, placebo-controlled, crossover clinical investigation to assess the potential for in vivo conversion of ranitidine to NDMA with different meals. A bioanalytical method toward characterization of NDMA formation was needed as previously published methods did not address potential NDMA formation after biofluid collection. Therefore, a bioanalytical method was developed and validated as per FDA's Bioanalytical Method Validation guidance. An appropriate surrogate matrix for calibration standards and quality control sample preparation for both liquid matrices (human plasma and urine) was optimized to minimize the artifacts of assay measurements and monitor basal NDMA levels. Interconversion potential of ranitidine to NDMA was monitored during method validation by incorporating the appropriate quality control samples. The validated methods for NDMA were linear from 15.6 pg/mL to 2000 pg/mL. Low sample volumes (2 mL for urine and 1 mL for plasma) made this method suitable for clinical study samples and helped to evaluate the influence of ranitidine administration and meal types on urinary excretion of NDMA in human subjects.

The US Food and Drug Administration (FDA) has taken steps to bring efficiency to the development of biosimilars, including establishing guidance for the use of pharmacokinetic and pharmacodynamic (PD) similarity study data without a comparative clinical study with efficacy end point(s). To better understand the potential role for PD biomarkers in biosimilar development and inform best practices for biomarker selection and analysis, we conducted a randomized, double-blinded, placebo-controlled, single-dose, parallel-arm clinical study in healthy participants. Eighty-four healthy participants (n = 12 per dose arm) received either placebo or one of three doses of either interferon beta-1a (7.5-30 mu g) or pegylated interferon beta-1a (31.25-125 mu g) to evaluate the maximum change from baseline and the baseline-adjusted area under the effect curve for the biomarkers neopterin in serum and myxovirus resistance protein 1 in blood. Both PD biomarkers increased following product administration with clear separation from baseline (neopterin: 3.4-fold and 3.9-fold increase for interferon beta-1a and pegylated interferon beta-1a, respectively; myxovirus resistance protein 1: 19.0-fold and 47.2-fold increase for interferon beta-1a and pegylated interferon beta-1a, respectively). The dose-response curves support that therapeutic doses were adequately sensitive to detect differences in both PD biomarkers for consideration in a PD similarity study design. Because baseline levels of both biomarkers are low compared with on-treatment values, there was little difference in using PD measures adjusted to baseline compared with the results without baseline adjustment. This study illustrates potential methodologies for evaluating PD biomarkers and an approach to address information gaps when limited information is publicly available for one or more PD biomarkers.

The U.S. Food and Drug Administration (FDA) Division of Applied Regulatory Science (DARS) moves new science into the drug review process and addresses emergent regulatory and public health questions for the Agency. By forming interdisciplinary teams, DARS conducts mission-critical research to provide answers to scientific questions and solutions to regulatory challenges. Staffed by experts across the translational research spectrum, DARS forms synergies by pulling together scientists and experts from diverse backgrounds to collaborate in tackling some of the most complex challenges facing FDA. This includes (but is not limited to) assessing the systemic absorption of sunscreens, evaluating whether certain drugs can convert to carcinogens in people, studying drug interactions with opioids, optimizing opioid antagonist dosing in community settings, removing barriers to biosimilar and generic drug development, and advancing therapeutic development for rare diseases. FDA tasks DARS with wide ranging issues that encompass regulatory science; DARS, in turn, helps the Agency solve these challenges. The impact of DARS research is felt by patients, the pharmaceutical industry, and fellow regulators. This article reviews applied research projects and initiatives led by DARS and conducts a deeper dive into select examples illustrating the impactful work of the Division.

US Food and Drug Administration (FDA) guidance outlines how biosimilars can be developed based on pharmacokinetic (PK) and pharmacodynamic (PD) similarity study data in lieu of a comparative clinical efficacy study. There is a paucity of PD comparability studies in biosimilar development, leaving open questions about how best to plan these studies. To that end, we conducted a randomized, double‐blinded, placebo‐controlled, single‐dose, parallel‐arm clinical study in healthy participants to evaluate approaches to address information gaps, inform analysis best practices, and apply emerging technologies in biomarker characterization. Seventy‐two healthy participants ( n = 8 per arm) received either placebo or one of four doses of the proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors alirocumab (15–100 mg) or evolocumab (21–140 mg) to evaluate the maximum change from baseline (ΔPD max ) and the baseline‐adjusted area under the effect curve (AUEC) for the biomarkers low‐density lipoprotein cholesterol (LDL‐C) and apolipoprotein B (apoB) in serum. We investigated approaches to minimize variability in PD measures. Coefficient of variation was lower for LDL‐C than apoB at therapeutic doses. Modeling and simulation were used to establish the dose–response relationship and provided support that therapeutic doses for these products are adequately sensitive and are on the steep part of the dose–response curves. Similar dose–response relationships were observed for both biomarkers. ΔPD max plateaued at lower doses than AUEC. In summary, this study illustrates how pilot study data can be leveraged to inform appropriate dosing and data analyses for a PK and PD similarity study.

ICH S7B recommends screening for hERG channel block using patch clamp recordings to assess a drug's proarrhythmic risk. Block of the hERG channel has been associated with clinical QTC prolongation as well as the rare, but potentially fatal ventricular tachyarrhythmia Torsade de Pointes (TdP). During recording, drug concentrations perfused to the cells can deviate from nominal concentrations due to molecule-specific properties (such as non-specific binding), thereby introducing error when assessing drug potency. To account for this potential source of error, both the original ICH S7B and the newly released ICH E14/S7B Q&As guidelines call for verifying drug solutions' concentrations. Dofetilide, cisapride, terfenadine, sotalol and E-4031 are hERG blockers commonly used as positive controls to illustrate hERG assay sensitivity. The first four compounds are also clinical drugs associated with high TdP risk; therefore, their safety margins may be useful comparators to better understand an investigational product's TdP risk. Having analytical methods to quantify these five compounds in the hERG external solution that will be used for patch clamp recordings is important from a regulatory science research perspective. However, a literature search revealed no analytical methods or stability information for these molecules in the high salt, serum-free matrix that constitutes the hERG external solution. This study was conducted to develop and validate LC-MS/MS methods to quantify these 5 molecules in hERG external solution. The bioanalytical methods for these positive controls were validated as per the FDA's bioanalytical method validation guidance along with various stabilities.

Evaluating the dermal absorption of sunscreen UV filters requires the development of a bio-predictable in vitro permeation test (IVPT). This work describes the comparison of two IVPT methods and rank order correlations of in vitro absorption (skin permeation and retention) with the in vivo absorption (AUC and skin retention) of sunscreens. The IVPT was compared regarding the following elements: (1) application of a single finite dose vs. an infinite dose and (2) the use of heat-separated human epidermis vs. dermatomed skin models. The IVPT was used to evaluate dermal absorption of six UV filters (avobenzone, homosalate, octinoxate, octisalate, octocrylene, and oxybenzone) in commercial sunscreens. Both the in vivo and in vitro permeation studies demonstrated that all UV filters were absorbed following a single-dose application. Sunscreens were rank ordered by the amount of the UV filters absorbed. Data obtained from the IVPT method using a single finite dose and heat-separated human epidermis was found to correlate with the clinical data. Rank orders of the cumulative in vitro skin permeation and the in vivo AUC were found comparable for oxybenzone, homosalate, octisalate, and octinoxate. Rank orders of the in vitro and in vivo skin retention of oxybenzone and octinoxate were also comparable. Additional IVPT parameters may be optimized to enhance the discriminatory power for UV filters with low skin permeation potential (e.g., avobenzone and octocrylene).

According to the ICH S7B guideline, drug candidates are screened for hERG block prior to first-in-human testing to predict the likelihood of delayed repolarization associated with a rare, but life-threatening, ventricular tachyarrhythmia. The new ICH E14 Q&As guideline allows hERG results to be used in later clinical development for decision-making (Q&As 5.1 and 6.1). To pursue this path, the hERG assay should be conducted following the new ICH S7B Q&A 2.1 guideline, which calls for best practice considerations of the recording temperature, voltage protocol, stimulation frequency, recording/data quality, and concentration verification. This study investigated hERG block by cisapride, dofetilide, terfenadine, sotalol, and E-4031 - positive controls commonly used to demonstrate assay sensitivity - using the manual whole cell patch clamp method and an action potential -like voltage protocol presented at 0.2 Hz. Recordings were conducted at room and near physiological temper-ature. Drug concentrations were measured using samples collected during real patch clamp experiments and satellite experiments. Results showed temperature effects for E-4031, terfenadine, and sotalol, but not cisapride and dofetilide. Cisapride and terfenadine showed substantial concentration losses, largely due to nonspecific binding to the perfusion apparatus. Using concentrations measured from the real and satellite experiments to assess block potencies yielded comparable results, indicating that satellite sample collection may be viable for drugs with nonspecific binding concerns only. In summary, this study provides block potencies for 5 hERG positive controls, and serves as a case study for hERG assays conducted, and results illustrated in accordance with the new ICH E14/S7B Q&As.

Importance Opioids can cause severe respiratory depression by suppressing feedback mechanisms that increase ventilation in response to hypercapnia. Following the addition of boxed warnings to benzodiazepine and opioid products about increased respiratory depression risk with simultaneous use, the US Food and Drug Administration evaluated whether other drugs that might be used in place of benzodiazepines may cause similar effects. Objective To study whether combining paroxetine or quetiapine with oxycodone, compared with oxycodone alone, decreases the ventilatory response to hypercapnia. Design, Setting, and Participants Randomized, double-blind, crossover clinical trial at a clinical pharmacology unit (West Bend, Wisconsin) with 25 healthy participants from January 2021 through May 25, 2021. Interventions Oxycodone 10 mg on days 1 and 5 and the following in a randomized order for 5 days: paroxetine 40 mg daily, quetiapine twice daily (increasing daily doses from 100 mg to 400 mg), or placebo. Main Outcomes and Measures Ventilation at end-tidal carbon dioxide of 55 mm Hg (hypercapnic ventilation) using rebreathing methodology assessed for paroxetine or quetiapine with oxycodone, compared with placebo and oxycodone, on days 1 and 5 (primary) and for paroxetine or quetiapine alone compared with placebo on day 4 (secondary). Results Among 25 participants (median age, 35 years [IQR, 30-40 years]; 11 female [44%]), 19 (76%) completed the trial. The mean hypercapnic ventilation was significantly decreased with paroxetine plus oxycodone vs placebo plus oxycodone on day 1 (29.2 vs 34.1 L/min; mean difference [MD], -4.9 L/min [1-sided 97.5% CI, -∞ to -0.6]; P = .01) and day 5 (25.1 vs 35.3 L/min; MD, -10.2 L/min [1-sided 97.5% CI, -∞ to -6.3]; P < .001) but was not significantly decreased with quetiapine plus oxycodone vs placebo plus oxycodone on day 1 (33.0 vs 34.1 L/min; MD, -1.2 L/min [1-sided 97.5% CI, -∞ to 2.8]; P = .28) or on day 5 (34.7 vs 35.3 L/min; MD, -0.6 L/min [1-sided 97.5% CI, -∞ to 3.2]; P = .37). As a secondary outcome, mean hypercapnic ventilation was significantly decreased on day 4 with paroxetine alone vs placebo (32.4 vs 41.7 L/min; MD, -9.3 L/min [1-sided 97.5% CI, -∞ to -3.9]; P < .001), but not with quetiapine alone vs placebo (42.8 vs 41.7 L/min; MD, 1.1 L/min [1-sided 97.5% CI, -∞ to 6.4]; P = .67). No drug-related serious adverse events were reported. Conclusions and Relevance In this preliminary study involving healthy participants, paroxetine combined with oxycodone, compared with oxycodone alone, significantly decreased the ventilatory response to hypercapnia on days 1 and 5, whereas quetiapine combined with oxycodone did not cause such an effect. Additional investigation is needed to characterize the effects after longer-term treatment and to determine the clinical relevance of these findings. Trial Registration ClinicalTrials.gov Identifier: NCT04310579.

Following a decision to require label warnings for concurrent use of opioids and benzodiazepines and increased risk of respiratory depression and death, the US Food and Drug Administratioin (FDA) recognized that other sedative psychotropic drugs may be substituted for benzodiazepines and be used concurrently with opioids. In some cases, data on the ability of these alternatives to depress respiration alone or in conjunction with an opioid are lacking. A nonclinical in vivo model was developed that could detect worsening respiratory depression when a benzodiazepine (diazepam) was used in combination with an opioid (oxycodone) compared to the opioid alone based on an increased arterial partial pressure of carbon dioxide (pCO(2)). The current study used that model to assess the impact on respiration of non-benzodiazepine sedative psychotropic drugs representative of different drug classes (clozapine, quetiapine, risperidone, zolpidem, trazodone, carisoprodol, cyclobenzaprine, mirtazapine, topiramate, paroxetine, duloxetine, ramelteon, and suvorexant) administered alone and with oxycodone. At clinically relevant exposures, paroxetine, trazodone, and quetiapine given with oxycodone significantly increased pCO(2) above the oxycodone effect. Analyses indicated that most pCO(2) interaction effects were due to pharmacokinetic interactions resulting in increased oxycodone exposure. Increased pCO(2) recorded with oxycodone-paroxetine co-administration exceeded expected effects from only drug exposure suggesting another mechanism for the increased pharmacodynamic response. This study identified drug-drug interaction effects depressing respiration in an animal model when quetiapine or paroxetine were co-administered with oxycodone. Clinical pharmacodynamic drug interaction studies are being conducted with these drugs to assess translatability of these findings.