Assessment of exposure of metabolites in preclinical species and humans at steady state from the single-dose radiolabeled absorption, distribution, metabolism, and excretion studies: a case study

Metabolite Bioanalysis in Drug Development: Recommendations from the IQ Consortium Metabolite Bioanalysis Working Group

The intent of this perspective is to share the recommendations of the International Consortium for Innovation and Quality in Pharmaceutical Development Metabolite Bioanalysis Working Group on the fit-for-purpose metabolite bioanalysis in support of drug development and registration. This report summarizes the considerations for the trigger, timing, and rigor of bioanalysis in the various assessments to address unique challenges due to metabolites, with respect to efficacy and safety, which may arise during drug development from investigational new drug (IND) enabling studies, and phase I, phase II, and phase III clinical trials to regulatory submission. The recommended approaches ensure that important drug metabolites are identified in a timely manner and properly characterized for efficient drug development.

Absorption, distribution, metabolism, and excretion of [14C]-dasotraline in humans

Dasotraline is a dopamine and norepinephrine reuptake inhibitor, and the early clinical trials show a slow absorption and long elimination half‐life. To investigate the absorption, distribution, metabolism, and excretion of dasotraline in humans, a single dose of [¹⁴C]‐dasotraline was administered to eight healthy male adult volunteers. At 35 days, 90.7% of the dosed radioactivity was recovered in the urine (68.3%) and feces (22.4%). The major metabolic pathways involved were: (1) amine oxidation to form oxime M41 and sequential sulfation to form M42 or glucuronidation to form M43; (2) N‐hydroxylation and sequential glucuronidation to form M35; (3) oxidative deamination to form (S)‐tetralone; (4) mono‐oxidation of (S)‐tetralone and sequential glucuronidation to form M31A and M32; and (5) N‐acetylation to form (1R,4S)‐acetamide M102. A total of 8 metabolites were detected and structurally elucidated with 4 in plasma (M41, M42, M43, and M35), 7 in urine (M41, M42, M43, M31A, M32, M35, and (S)‐tetralone), and 3 in feces (M41, (S)‐tetralone, and (1R,4S)‐acetamide). The 2 most abundant circulating metabolites were sulfate (M42) and glucuronide (M43) conjugates of the oxime of dasotraline, accounting for 60.1% and 15.0% of the total plasma radioactivity, respectively; unchanged dasotraline accounted for 8.59%. The oxime M41 accounted for only 0.62% of the total plasma radioactivity and was detected only at early time points. M35 was a minor glucuronide metabolite, undetectable by radioactivity but identified by mass spectrometry. The results demonstrate that dasotraline was slowly absorbed, and extensively metabolized by oxidation and subsequent phase II conjugations. The findings from this study also demonstrated that metabolism of dasotraline by humans did not produce metabolites that may cause a safety concern.

Human absorption, distribution, metabolism and excretion properties of drug molecules: a plethora of approaches

Human radiolabel studies are traditionally conducted to provide a definitive understanding of the human absorption, distribution, metabolism and excretion (ADME) properties of a drug. However, advances in technology over the past decade have allowed alternative methods to be employed to obtain both clinical ADME and pharmacokinetic (PK) information. These include microdose and microtracer approaches using accelerator mass spectrometry, and the identification and quantification of metabolites in samples from classical human PK studies using technologies suitable for non-radiolabelled drug molecules, namely liquid chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy. These recently developed approaches are described here together with relevant examples primarily from experiences gained in support of drug development projects at GlaxoSmithKline. The advantages of these study designs together with their limitations are described. We also discuss special considerations which should be made for a successful outcome to these new approaches and also to the more traditional human radiolabel study in order to maximize knowledge around the human ADME properties of drug molecules.

The debate on animal ADME studies in drug development: an update

The preparation and release of the International Conference on Harmonisation guideline on safety evaluation of human metabolites and the technical progresses in bioanalysis have triggered an intense debate on the value of absorption, distribution, metabolism and excretion radiolabelled studies in animals. Some authors have radically challenged the traditional approach whereas others, while accepting the need of significant changes, argue that these studies remain an irreplaceable component of the preclinical registration dossier. This paper reviews some of the representative positions and describes the potential evolution.

Evaluation of lixivaptan in euvolemic and hypervolemic hyponatremia and heart failure treatment

INTRODUCTION

Lixivaptan is a selective vasopressin type 2 (V2) receptor antagonist that induces aquaresis, the electrolytes sparing excretion of water. Its ability to correct hyponatremia has been demonstrated in experimental animal studies as well as in clinical trials in humans. Recently, three Phase III, double-blind, randomized, placebo-controlled studies have been completed. In two studies, patients with euvolemic hyponatremia were enrolled, one in the inpatient and the other in the outpatient setting and the third study involved patients with hypervolemic hyponatremia hospitalized for decompensated heart failure (HF). The trials confirmed the efficacy of lixivaptan in raising serum sodium but raised concern about its safety in patients hospitalized with decompensated HF.

AREAS COVERED

The authors review original publications on lixivaptan and summarize their findings. Specifically, the authors present information regarding its structure, pharmacodynamics and kinetics, metabolism as well as its efficacy and safety in laboratory animals and human studies. Furthermore, the FDA website was accessed to obtain information presented at the September 13, 2012 meeting of the Cardiovascular and Renal Drugs Advisory Committee.

EXPERT OPINION

The published data indicate that lixivaptan raises sodium levels in hyponatremic patients and supports its use in patients with euvolemic hyponatremia. However, the authors note that more safety data are still needed specifically in patients with decompensated HF.