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Absolute Bioavailability

• Bioavailability is one of the essential tools in pharmacokinetics.
• Regulatory authorities have provided guidance for bioavailability information for orally administered drug products in new drug applications.

Typical bioavailability studies (non-AMS) are costly and challenging. Without AMS, bioavailability studies are generally conducted using a two-way crossover design, thus requiring dosing times sufficiently separated to ensure clearance between the two dosing modes. Additionally, preparation of an IV formulation for a cross over study design presents a significant obstacle.

These issues can be overcome using a microdose design which incorporates 14C labeled drug product at sub-pharmacologic concentrations (<100 µg), with a pharmacologic oral dose of cold drug product simultaneously. Microdosing allows for parallel oral and IV assays performed on single PK specimens as well as easing the IV formulation challenges. Accelerator mass spectrometry allows for the routine, precise, and accurate quantitation of the sub-pharmacologic concentrations of a drug product.

AMS methods can be used to generate the IV area under the curve (AUC), whle standard LCMS/MS metheods can still be used to generate the oral AUC. Bioavailability is calculated by normalizing the IV AUC to the oral dose size and calculating the ratio obtained from the oral AUC and the normalized IV AUC.

14C label studies allow for an elegant assessment of absolute bioavailability in human subjects, eliminate variability introduced in crossover designs, and reduce the number of specimens that must be collected and time study subjects spend at the clinic. 14C label studies also avoid the challenges of developing IV formulations at pharmacologic concentrations. All of this translates into shorter release timelines and fewer incurred costs.

Accium BioSciences has has successfully delivered on a wide range of AMS based absolute bioavailability balance studies. Each study is customized to address particular challenges specific to each program.

Clinical Design

    • Six to eight subjects.
    • Single dose of unlabeled drug product administered orally at the pharmacologic dose.
    • Single <100 µg dose of ~100 nCi 14C labeled drug product administered by infusion around the oral dose Cmax.
    • Collect 2-4 mL plasma for LCMS/MS analysis of orally administered drug product.
    • Collect 1-2 mL plasma for AMS analysis of IV administered drug product.

Pre-study Phase

    • Transfer/develop extraction and HPLC procedures to Accium BioSciences.
    • Transfer unlabeled and 14C labeled drug reference standards to Accium BioSciences.
    • Demonstrate acceptable chromatographic conditions by UVHPLC (using spiked unlabeled references).
    • Demonstrate acceptable recovery through extraction and HPLC by AMS (using spiked 14C labeled references).
    • Calibrator and quality control standards qualified in a manner described in regulatory bioanalytical guidelines.

Study Phase

    • Extract all plasma samples, fractionate by HPLC, and quantify by AMS.
    • Incorporate calibrator and/or quality control standards within each batch of analysis.
    • Accept or reject the analysis batch based on established criteria for the quality control samples.
    • Normalize the concentrations of unknown plasma samples using a qualified standard curve equation.
    • Report radioactivity concentration in units best suited to the sponsor’s needs (e.g., DPM/mL, ng-Eq/mL).


    • Reduces or eliminates IV dose formulation challenges.
    • Concomitant administration of oral and intravenous dose reduces within-subject variability.
    • Reduces clinical costs due fewer visits/time spent at the clinic.
    • Samples are treated as nonradioactive and may be processed in any laboratory.