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    Bioavailability after intravenous administration (by definition 100%, red, i.v.) and after oral administration (black, grey, p.o.): If the areas under the curves for the period are equal for both methods of administration, the oral bioavailability also corresponds to 100% (grey area under black curve). Smaller areas correspond to lower bioavailability. drug concentration in plasma, time.

    Bioavailability is a key concept in pharmacology and nutrition, referring to the rate and extent to which a substance is absorbed into the bloodstream and made available at the site of physiological activity. This concept is crucial for both pharmaceuticals and nutraceuticals, as it determines the effectiveness of drugs and dietary supplements.

    Definition and Significance

    Bioavailability is a term used to describe the proportion of a nutrient or medication that, after being administered, enters the circulation and is thus able to exert its intended effect. This measure is essential for understanding the efficacy of any compound taken orally, intravenously, or through other routes of administration.

    • For Pharmaceuticals: In medication, high bioavailability ensures that a drug can effectively target the intended site in the body.
    • For Nutraceuticals: In dietary supplements, it determines how well a nutrient is absorbed and utilized by the body.

    Factors Affecting Bioavailability

    Several factors can influence the bioavailability of a substance:

    • Chemical Form: The molecular structure of a compound can significantly affect its absorption. For example, certain vitamins are better absorbed in specific forms.
    • Route of Administration: Oral, intravenous, sublingual, and topical are different ways drugs can be administered, each with varying bioavailability.
    • Metabolism: First-pass metabolism in the liver can reduce the concentration of a substance before it reaches systemic circulation.
    • Solubility: Water-soluble compounds tend to have higher bioavailability than fat-soluble ones.
    • Interactions: Interactions with other substances, like food or other drugs, can enhance or hinder absorption.

    Measuring Bioavailability

    Bioavailability is often assessed through specific pharmacokinetic studies, which evaluate the concentration of a drug in plasma over time. The two key metrics used are absolute and relative bioavailability.

    Absolute Bioavailability

    This measures the bioavailability of a drug compared to its intravenous administration. The formula for calculating absolute bioavailability (F) is:

    where AUC is the area under the plasma concentration-time curve for oral (AUCoral) and intravenous (AUCIV) administration, and Dose refers to the dose administered via each route.

    Relative Bioavailability

    Relative bioavailability compares the bioavailability of a drug in different formulations, typically against a standard or reference formulation. The formula is:

    where AUCtest and AUCref are the areas under the curve for the test and reference formulations, respectively, and Dose is the dose for each.

    Factors Affecting Bioavailability

    Mechanism of micronutrient bioavailability in the human body [1]

    Bioavailability (F) of oral drugs or bioactive food components is influenced by several key stages: liberation, absorption, distribution, metabolism, and elimination. The equation representing bioavailability is:

    Where each factor represents a different aspect of how a substance is processed in the body:

    F Factor Description Influencing Factors Example
    FC Liberation The fraction of a micronutrient or drug that becomes available from its food matrix or dosage form in the GIT. Physical and chemical form of the substance, processing methods, interactions with other components. Reduced liberation of vitamin B12 from food sources in the elderly due to decreased stomach acid production, impacting the release and subsequent absorption of B12.
    FB Bioaccessibility The portion of the substance that is released from the food product or dosage form and dissolves in the GIT liquids. GIT pH and enzyme activity, solubility and stability of the nutrient or drug. Dissolution of an omega-3 fatty acid capsule in the intestinal fluid.
    FA Absorption The fraction of the substance that passes through the intestinal wall into the systemic circulation. Gastrointestinal mucosa integrity, presence of transporters and enzymes, physicochemical properties of the substance. Absorption of Coenzyme Q10 (CoQ10) is generally low due to its large molecular weight and fat solubility, making it better absorbed when taken with meals rich in fats.
    FM Metabolism The fraction of the substance that remains in a bioactive form after metabolic transformations. Enzymatic activity within the GIT, liver metabolism, systemic circulation, metabolic stability, and enzymatic degradation susceptibility. Resveratrol is rapidly metabolized in the liver into various metabolites, which may have reduced biological activity compared to the parent compound, affecting its overall bioavailability and potential health benefits.

    Each of these stages is crucial in determining the overall bioavailability of a substance, and they are influenced by the chemical breakdown of bioactive elements during processing, manufacture, storage, and transport, as well as interactions within the GIT.

    Improving Bioavailability

    Research and development in pharmaceutical and nutraceutical sciences focus on enhancing bioavailability through various means, including advanced delivery systems, chemical modifications, and combinational approaches.

    • Nano-Based Delivery Systems: Delivery systems utilizing of nanotechnology (e.g. liposomes, micelles) to enhance the delivery and bioavailability of various nutrients and bioactive components.
    • Chemical Modifications: Altering the chemical structure of a compound can increase its solubility and absorption, making the active ingredient more available in the systemic circulation.
    • Combinational Approaches: Using adjuvants or combining nutrients with enhancers can significantly improve bioavailability. This approach often involves synergistic combinations that enhance the overall effect of the active ingredients.


    Understanding and optimizing bioavailability is fundamental for the effectiveness of drugs and nutritional supplements. As research progresses, new methods and formulations continue to emerge, enhancing the efficacy of therapeutic and nutritional interventions.

    See Also


    • 2016, Excipient Nanoemulsions for Improving Oral Bioavailability of Bioactives [1]


    1. 1.0 1.1 Salvia-Trujillo L et al.: Excipient Nanoemulsions for Improving Oral Bioavailability of Bioactives. Nanomaterials (Basel) 2016. (PMID 28344274) [PubMed] [DOI] [Full text] The oral bioavailability of many hydrophobic bioactive compounds found in natural food products (such as vitamins and nutraceuticals in fruits and vegetables) is relatively low due to their low bioaccessibility, chemical instability, or poor absorption. Most previous research has therefore focused on the design of delivery systems to incorporate isolated bioactive compounds into food products. However, a more sustainable and cost-effect approach to enhancing the functionality of bioactive compounds is to leave them within their natural environment, but specifically design excipient foods that enhance their bioavailability. Excipient foods typically do not have functionality themselves but they have the capacity to enhance the functionality of nutrients present in natural foods by altering their bioaccessibility, absorption, and/or chemical transformation. In this review article we present the use of excipient nanoemulsions for increasing the bioavailability of bioactive components from fruits and vegetables. Nanoemulsions present several advantages over other food systems for this application, such as the ability to incorporate hydrophilic, amphiphilic, and lipophilic excipient ingredients, high physical stability, and rapid gastrointestinal digestibility. The design, fabrication, and application of nanoemulsions as excipient foods will therefore be described in this article.