In Vivo ADME Studies

In vivo ADME studies are conducted with a radiolabel to provide quantitative information on the rate and extent of metabolism, routes of excretion for parent compound and its metabolites, and circulating metabolites. Nonclinical in vivo ADME studies can be conducted in either rodents and non-rodents, depending on the species used in toxicology studies. The dosage, route of administration, and formulations should be identical to safety studies.

Although radiolabeled and non-radiolabeled in vivo ADME studies are not required as part of an IND package, the information produced can be extremely important in explaining the relative clinical safety/risk to the FDA or other regulators. Alternatively, these studies may be conducted later in development if the data isn’t critical to the IND process, as they are required for NDA filing.

Study Design Options

    • Pharmacokinetics/toxicokinetics (PK/TK)
    • Excretion, mass balance, and expired air collection in rodents
    • Quantitative tissue distribution (traditional method and QWBA) with dosimetry calculations
    • Bioavailability
    • Micro-autoradiography (to determine cellular distribution)
    • Placental transfer and milk secretion
    • Various surgical models, including bile duct cannulation
    • Metabolite profiling and identification
    • Radioactivity sample analysis
    • Oral
    • Intravenous
    • Subcutaneous
    • Intramuscular
    • (Trans)dermal
    • Intraperitoneal
    • Oropharyngeal
    • Intratracheal
    • Intranasal
    • Continuous infusion
    • Intravitreal
    • Ocular
    • Intrathecal
    • Portal vein (via access ports)
    • Intraduodenal
    • Inhalation
    • Vascular access ports
    • Chronic bile duct cannulation
    • Intestinal cannulation
    • Portal vein cannulation
    • 3H
    • 14C
    • 32P
    • 35S
    • 125I
    • Additional ones are available, upon request


Regulatory Package

The following in vivo components are typically involved in an ADME package.


    Mass balance studies provide important information regarding absorption, biodistribution, metabolism, and excretion of compounds. The purpose of these studies is not only to understand the biodistribution and metabolism, but also how both parent and metabolites are eliminated from the body and whether either parent or metabolites accumulate in any tissues or fluids (lymph, milk, saliva, etc.). These in vivo ADME studies are typically single dose studies utilizing a radiolabel with sample collection up to a week, but samples may be collected for a longer period of time if the drug has a longer half-life.

    Urine and fecal samples are collected during the study to analyze for radioactivity and metabolite profiling. Metabolic profiles of the samples are generated by a combination of techniques, such as HPLC radioactivity detection, LC fractionation followed by scintillation counting, and LC-MS coupled to radioactivity detection. Each study is designed to assess the extent of absorption, the important metabolic pathways, the role of the kidney or liver in elimination, and whether any metabolites are formed which have safety or efficacy concerns.

    The data can accurately calculate the exposure to metabolites, identify major ones, measure the half-life of metabolites that could potentially result in accumulation when administered repeatedly, and provide information about metabolites that would enable comparison between toxicology species and humans.


    By taking blood samples concomitantly (non-rodents) or as separate groups (rodents) in the mass-balance phase, these samples can be used to establish pharmacokinetics of drug-related material and establish metabolite profiles to identify the major circulating metabolites. Understanding the pharmacokinetics of all drug-related material creates an important bridge between ADME and toxicology studies.


    Biliary excretion studies are performed to understand the excretion of the drug and its metabolites via bile. These in vivo ADME studies indicate whether the drug is unabsorbed and excreted via the feces or whether the drug is absorbed and excreted via the bile into the feces. These studies will help further refine the extent of absorption, and can offer insight into metabolism by the subject versus their GI microbiome. We can offer customized studies using bile duct cannulated rats and large animals.


    Elucidation of drug distribution in preclinical species can help identify potential target tissues for toxicity or confirm suitable exposure of the therapeutic target. Our scientists can support you in procuring this information with the effective design, conduct, and delivery of traditional wet tissue distribution or Quantitative Whole-Body Autoradiography (QWBA) studies as part of our preclinical drug metabolism service.

    QWBA is typically regarded as the technique of choice for determining the distribution of drug-related material in laboratory animals as the response of the phosphor screen to radioactivity has been shown to be quantitative over at least five orders of magnitude and the high-resolution digital image obtained can be enlarged to provide greater depth and detail of distribution across and within the tissues or organ of interest.


    In the case of non-radiolabeled ADME studies, bioanalytical method validation of the different matrix samples is performed and samples are analyzed utilizing analytical techniques, such as LC-MS, ICP-MS, and GC-MS. When performing ADME studies with radiolabeled compounds, radioanalysis can be combined with bioanalysis to quantify the parent compound and derive data on extent of metabolism.

    Our dedicated radioanalysis laboratories can support the analysis of radioactive samples from animal and human radiolabeled studies either by directly measuring gamma-emitting compounds or beta-emitting compounds, or by solubilization or oxidation for measuring beta-emitting compounds. Total radioactivity can be further profiled via HPLC with radiochemical detection.

    The DEBRA® data management system provides electronic data collection and evaluation, and is integrated with high-throughput robotic sample handling and radioanalysis instrumentation. Our team analyzes samples from studies conducted at any one of our facilities as well as samples delivered from outside sources as a stand-alone service, with rapid real-time testing.


    Early information on metabolite profiling and structural elucidation of metabolites from in vitro and in vivo metabolism studies can help improve compound design plus the efficacy and safety properties of a lead drug candidate, chemical, or veterinary product. An active metabolite may bind to therapeutic target receptors, interact with other targets, and cause unintended effects; therefore, it’s important to identify differences as early as possible in metabolism between nonclinical species and humans to avoid development and clinical delays.

    The task of detecting and characterizing metabolites in complex biological samples is challenging due to coexisting test item-related material and endogenous material, and requires not only sophisticated LC-MS technology, but also software to interpret the MS data. Our scientists design bespoke experiments to overcome unique and complex analytical challenges to help profile, isolate, analyze, and identify metabolites, in support of discovery and safety studies.

    Charles River provides insightful and valuable ADME services. With a team of more than 400 dedicated ADME scientists and experience across the complete range of in vitro and in vivo metabolism studies in support of hit-to-lead, candidate discovery, and selection for preclinical testing and clinical development programs, we are here to meet all your program needs.

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Frequently Asked Questions (FAQs) about In Vivo ADME Studies

  • How do in vivo ADME studies enable better clinical outcomes?

    Absorption, distribution, metabolism, and excretion (ADME) properties in the past attributed to more drug failures than efficacy or safety in clinic trials. With the use of new and improved techniques, more informed predictions for the pharmacokinetic properties of compounds in humans are being made, shifting drug failure more to the safety and efficacy characteristics of drug candidates. Radiolabeled and non-radiolabeled in vivo ADME studies can not only characterize compounds but select and understand the clinical implications, support pharmacology and toxicology, and optimize a drug candidate.

  • Why are radiolabeled in vivo ADME studies necessary?

    Radiolabeled in vivo ADME studies still provide a definitive and unique component of our understanding of the in vivo actions and behaviors of drugs, providing critical information prior to the exposure of large numbers of human subjects to investigative drugs. The understanding of the in vivo pharmacological activity and disposition of new drug candidates, including interpretation of preclinical toxicology findings, characterization of circulating metabolites, and determination of principal pathways of clearance are some of the benefits of running radiolabeled in vivo ADME studies. This understanding is valuable in anticipating the human disposition of the drugs and the planning of a clinical development program.