What is the Difference Between Bioavailability and Bioequivalence

Bioavailability and bioequivalence are two critical concepts in pharmacology and pharmaceutical science. Both play an important role in understanding the effectiveness and safety of drugs.

What is the difference between bioavailability and bioequivalence? Bioavailability refers to the proportion of a drug or substance that enters the bloodstream when introduced into the body, thus having an active effect. Bioequivalence, on the other hand, compares the bioavailability of two formulations of the same drug.

Key Areas Covered

1. What is Bioavailability  
     – Definition, Facts, Features
2. What is Bioequivalence
     – Definition, Facts, Features
3. Similarities Between Bioavailability and Bioequivalence
     – Outline of Common Features
4. Difference Between Bioavailability and Bioequivalence
     – Comparison of Key Differences
5. FAQ – Bioavailability and Bioequivalence
     – Answers to Frequently Asked Questions

Key Terms

Bioavailability, Bioequivalence, Pharmacology, Drugs

Difference Between Bioavailability and Bioequivalence - Comparison Summary

What is Bioavailability

Bioavailability refers to the proportion of a nutrient or substance that enters the bloodstream when introduced into the body and is made available for use or storage. It is a crucial concept in pharmacology, nutrition, and toxicology, influencing the effectiveness of medications, nutrients, and other compounds.

In pharmaceuticals, bioavailability is a key factor in determining the dosage and administration of drugs. Different forms of medication, such as pills, liquids, or injections, can have varying bioavailabilities. Factors like the administration route, the drug’s formulation, and interactions with other substances in the body all contribute to this variability.


Figure 1: Bioavailability after Intravenous Administration (i.v) and after Oral Administration (p.o)

In nutrition, bioavailability plays a major role in understanding how effectively the body can absorb and utilize nutrients from the food we consume. Certain nutrients may have higher bioavailability in specific food sources or when consumed with particular nutrients. For example, the absorption of iron from plant-based sources is enhanced when consumed with vitamin C.

Moreover, bioavailability is critical in toxicology, as it influences how the body processes and eliminates harmful substances. The bioavailability of toxins can depend on factors such as the route of exposure and the chemical form of the toxin.

What is Bioequivalence

Bioequivalence refers to the similarity in the rate and extent to which the active ingredient in a pharmaceutical product is absorbed and becomes available at the site of action when compared to a reference product. In simpler terms, it assesses whether a generic drug is equivalent to its brand-name counterpart in terms of pharmacokinetic properties.


Figure: Bioequivalence of Bupropion

Pharmacokinetics involves the study of how a drug is absorbed, distributed, metabolized, and eliminated by the body. When a generic drug claims to be bioequivalent to a brand-name drug, it means that it produces similar blood concentration profiles of the active ingredient over time. This similarity ensures that the generic drug will have efficacy and safety comparable to the original product.

Similarities Between Bioavailability and Bioequivalence

  1. Both concepts are crucial in pharmaceutical development and regulatory approval processes.
  2. They are essential considerations in optimizing drug efficacy and safety.
  3. Both involve the measurement and comparison of drug concentrations in the bloodstream.
  4. Bioavailability and bioequivalence studies are conducted to ensure consistent and predictable drug performance.

Difference Between Bioavailability and Bioequivalence


  • Bioavailability refers to the rate and extent to which an active ingredient is absorbed and becomes available at the site of action. On the other hand, bioequivalence compares the bioavailability of two formulations (typically a generic and a brand-name drug) to ensure they are therapeutically equivalent.


  • While bioavailability is concerned with the absorption, distribution, metabolism, and excretion of a drug within the body, bioequivalence specifically assesses the similarity in rate and extent of drug absorption between two formulations.


  • Bioavailability studies often involve comparing different formulations or routes of administration for the same drug. On the other hand, bioequivalence studies typically involve comparing a generic drug to its brand-name counterpart under carefully controlled conditions.


The difference between bioavailability and bioequivalence lies in their focus and application. Bioavailability measures substance absorption, distribution, metabolism, and excretion, affecting effectiveness. Bioequivalence compares the therapeutic similarity of two formulations, ensuring similar absorption rates. Both are crucial for drug optimization and dosage determination.

FAQ: Bioavailability and Bioequivalence

1. What is an example of bioavailability?

For example, when morphine is administered orally, only about 25 percent of the drug reaches the systemic circulation because a substantial portion undergoes first-pass metabolism in the liver before entering the bloodstream.

2. Which drug has 100% bioavailability?

Drugs having 100% bioavailability include chlordiazepoxide, diazepam, lithium, metronidazole, phenobarbitol, salicylic acid, trimethoprim, and valproic acid.

3. What causes poor bioavailability?

Low bioavailability is most common with oral dosage forms of poorly water-soluble, slowly absorbed drugs. Insufficient time for absorption in the gastrointestinal (GI) tract is a common cause of low bioavailability.

4. What are the factors that affect bioavailability?

Drug bioavailability after oral administration is affected by many different factors, including physicochemical properties of the drug, physiological aspects, the type of dosage form, food intake and biorhythms.

5. What is an example of bioequivalence?

An example of bioequivalence is when a generic version of a commonly used brand-name medication, like ibuprofen (Advil), shows similar absorption rates and levels in the bloodstream when given at the same dose and under similar conditions during clinical testing.

1. “Drug Bioavailability.” National Library of Medicine.

Image Courtesy:

1. “AUC iv po” By Benff – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Bupropion bioequivalency comparison” By CMBJ – Own work based on FDA data (CC BY 3.0) via Commons Wikimedia

About the Author: Hasini A

Hasini is a graduate of Applied Science with a strong background in forestry, environmental science, chemistry, and management science. She is an amateur photographer with a keen interest in exploring the wonders of nature and science.

Leave a Reply