WHAT IS 'Bioavailability'

Bioavailability refers to the portion of a nutrient that reaches the human bloodstream. When discussing a drug, bioavailability can refer to either the percentage of a dose that reaches its target or the rate at which it achieves the bloodstream. Bioavailability can be an important factor in the efficacy and commercial viability of that drug.

BREAKING DOWN 'Bioavailability'

Bioavailability is a term taken from the field of pharmacokinetics, the study of the movement of drugs through the human body. In scientific notation, it is represented by a capital or lowercase F.  The term can describe the delivery of food nutrients to the circulatory system, which can be affected by a range of physiological variables such as body weight and metabolism. The pharmacological definition, however, is designed to assign an absolute bioavailability to each drug, consistent among identical dosages of that drug, and unaffected by those physiological factors. This definition can expressed by the following formula:

This formula compares the bioavailability of a drug taken intravenously (IV), with the same drug taken orally (oral). F refers to the absolute bioavailability of an oral dose. AUC refers to area under curve of the two dosages. This can be thought of as the amount of a dose that reaches the bloodstream. Since an IV dose reaches the bloodstream directly and in its entirety, its bioavailability is always 1. Thus, the bioavailability of an oral dose is expressed as a percentage of the bioavailability of an equivalent IV dose.

Variables that Affect Bioavailability

The above calculation of absolute bioavailability is meant to express the bioavailability of a particular compound free of physiological variables mentioned above. There are several variables, however, that differentiate the bioavailability of one drug from that of another. Most important is first pass metabolism, which refers to the process by which the drug is absorbed between its entry into the body and its entry into the bloodstream. This occurs most rapidly in the liver, and drugs taken orally travel most quickly to the liver.  

Another factor is the chemical stability of the compound. Relatively unstable drugs will break down more rapidly in the gastrointestinal tract, and may be better candidates for non-oral application.

A third variable, which may in some cases lead to bioavailability variability among identical compounds with different manufacturers, is the quality control or production techniques used by those labs. Particle size or the inclusion of diluents (thinning agents) or binding agents can affect drug absorbability from brand to brand.

Finally, the form of the dosage tends to impact bioavailability. Liquids generally are more bioavailable than solids, and gases surpass liquids. Pills tend to be the most marketable form, so manufacturers seek ways to boost the bioavailability of solids whenever possible. Possible solutions range from molecule variations to enhancements to the discovery and developments stages of a drug’s lifecycle. In recent years, solubility consultancies have emerged to aid manufacturers in improving their bioavailability as a competitive advantage in the marketplace.

  1. Biotech Compound

    A biotech compound is a chemical identified by scientists as ...
  2. Drug

    A drug is a substance that cures, treats, prevents or reduces ...
  3. Pharmacovigilance

    Pharmacovigilance refers to the scientific process through which ...
  4. Orphan Drug Credit

    The orphan drug credit helps pharmaceutical companies absorb ...
  5. Food And Drug Administration (FDA)

    The Food and Drug Administration is a government agency that ...
  6. Healthcare Sector

    The healthcare sector consists of companies that provide medical ...
Related Articles
  1. Insights

    How Pharmaceutical Companies Price Their Drugs

    Learn more about how pharmaceutical companies price drugs, why prices are often very high and why it can be difficult to settle on a suitable price.
  2. Investing

    Pharma Balks at German Price Control (BAYRY, RHHBY)

    Drug makers are worried about a proposed new German law that would tighten price controls on prescription drugs.
  3. Investing

    Using DCF In Biotech Valuation

    Valuing firms in this sector can seem like a black art, but there is a systematic way to pin a price on potential.
  4. Insights

    Drug Prices Gone Wild: Hospitals Feel Pain of Increases

    Hospitals and patients are suffering as prices soar for both branded and generic drugs
  5. Insights

    8 Stages Of New Drug Development

    Understanding biotech data isn't easy. What is a clinical trial, what are the various phases, and why do the results of these trials and applications often create double-digit moves in the price ...
  6. Insights

    The Industry Handbook: Pharma Industry

    Learn about the pharmaceutical industry and discover the forces that influence this highly profitable and dynamic sector.
  7. Investing

    Cost of Old Cancer Drugs Rises in EU Amid Outcry

    The prices of several off-patent cancer drugs have soared more than 100% in Europe.
  8. Investing

    Evaluating Pharmaceutical Companies

    Learn how to find a healthy pharmaceutical investment in a market full of weak drugs.
  9. Investing

    Drug Supply Chain May Be Driver of High Drug Prices

    Non-manufacturing stakeholders in the drug pricing system are the ones contributing to high prices.
  10. Insurance

    The Cancer (and Other Drug) Shortage

    Your doctor may not tell you, but even in the U.S., life-saving drugs can be in short supply. Here's what to know and do.
  1. What are the major barriers to entry for new companies in the drugs sector?

    Find out why barriers to entry for U.S. drug companies are so high and how the Food and Drug Administration, or FDA, inhibits ... Read Answer >>
  2. Can your insurance company drug test you?

    Learn why drug companies conduct drug tests and how a lifestyle free of drugs and alcohol can save you big money on health ... Read Answer >>
  3. What is the difference between direct costs and variable costs?

    Learn about variable costs and direct costs, how direct costs and variable costs are classified and the differences between ... Read Answer >>
  4. How does operating leverage affect business risk?

    Learn how operating leverage affects business risk and how companies measure it. Review a relevant example of operating leverage ... Read Answer >>
  5. Who are Pfizer's (PFE) main competitors?

    Learn about Pfizer's place in the pharmaceutical industry, and find out which major drug manufacturers are among its main ... Read Answer >>
Hot Definitions
  1. Yield Curve

    A yield curve is a line that plots the interest rates, at a set point in time, of bonds having equal credit quality, but ...
  2. Portfolio

    A portfolio is a grouping of financial assets such as stocks, bonds and cash equivalents, also their mutual, exchange-traded ...
  3. Gross Profit

    Gross profit is the profit a company makes after deducting the costs of making and selling its products, or the costs of ...
  4. Diversification

    Diversification is the strategy of investing in a variety of securities in order to lower the risk involved with putting ...
  5. Intrinsic Value

    Intrinsic value is the perceived or calculated value of a company, including tangible and intangible factors, and may differ ...
  6. Current Assets

    Current assets is a balance sheet item that represents the value of all assets that can reasonably expected to be converted ...
Trading Center