Bioavailability refers to the amount of drug absorbed relative to the quantity given. This is calculated as the ratio of drug exposure after equivalent doses of oral and intravenous forms of a drug are admininistered (to the same subjects). Exposure is measured on the kinetic graph as the area under the curve (AUC) of serum drug concentration over time. This is illustrated in the diagram on the right. The fraction of oral drug that makes it to the circulatory system is the bioavailability of that drug.
For IV drugs, the bioavailability is 100%
For oral medications, the bioavailability will be less than 100%, due in part to any of these reasons:
- Oral drugs have slower absorption and distribution than IV drugs.
- The amount of drug that is absorbed can depend on the status of the GI tract (stomach pH, presence of food, integrity/health of the intestines, speed of the GI tract, etc.)
- Oral drugs may be broken down by enzymes that are present anywhere along the GI tract.
If bioavailability is low then the oral dose needed has to be increased so that a given dose achieves the appropriate serum concentration. Since the absorption of an oral drug is slower than an IV drug and the drug takes longer to enter the circulation, clearing the drug will also most likely take a longer time.
FAQs
Absolute bioavailability is defined as 100% of the substance reaching the bloodstream, which can only be achieved through an intravenous (IV) means. Relative bioavailability is the amount of the substance that reaches the bloodstream through other means of administration, like oral and sublingual.
What is bioavailability pdf? ›
Bioavailability is a key pharmaco*kinetic parameter which expresses the proportion of a drug administered by any nonvascular route that gains access to the systemic circulation.
Is bioavailability 100 percent? ›
Bioavailability is a term used to describe the percentage (or the fraction F) of an administered dose of a xenobiotic that reaches the systemic circulation. Bioavailability is practically 100% (F=1) following an intravenous administration.
What is the bioavailability of an IV? ›
By definition, when a medication is administered intravenously, its bioavailability is 100%. However, when a medication is administered via routes other than intravenous, its bioavailability is lower due to intestinal epithelium absorption and first-pass metabolism.
What are three 3 factors that alter bioavailability? ›
Bioavailability depends on several factors, of which metabolism by the liver or gut, or the first-pass metabolism is the most prominent. Other factors include chemical stability, drug solubility and formulation.
How to calculate bioavailability? ›
- Equation 1: Vd = total amount of drug in the body ÷ plasma drug concentration. ...
- Equation 2: F = mass of the drug delivered to the plasma ÷ total mass of the drug administered. ...
- Equation 3: F = AUC for X route of administration ÷ AUC for IV administration.
The IDL ligands exhibited favourable bioavailability score of 0.55. In order to be considered a therapeutic candidate, a molecule typically needs to have a bioavailability score of at least 0.10 [39] .
What does 70 bioavailability mean? ›
Bioavailability is a pharmaco*kinetic parameter represented by the symbol "F" and is usually presented as % of the dose. For example, a bioavailability of 70% means 70% of the administered dose reaches the systemic circulation.
What foods are high in bioavailability? ›
Bioavailable Sources of Nutrients
Foods that scored “very high” included organ meats, shellfish, small fish, dark leafy greens, goat, beef, eggs, cow milk, and cheese. A few things to say about the data: Organ meats (especially liver) and bivalves were the highest-scoring foods.
What is bad 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.
Bioavailability of vitamin D differs among individuals due to variable absorption or altered metabolism in the body (2). For example, it is influenced by several different factors after ingestion including gastric pH, gastric enzymes including pepsin and trypsin, and duodenal enzymes (proteases, amylase, and lipase).
How to increase bioavailability? ›
The bioavailability of poorly absorbed drugs can be improved by formulating the drugs into nanosuspensions, solid lipid nanoparticles, polymeric nano- and microparticles, liposomes, niosomes, phytosomes, self-micro emulsifying drug delivery system and microemulsion.
What is bioavailability in simple terms? ›
The ability of a drug or other substance to be absorbed and used by the body. Orally bioavailable means that a drug or other substance that is taken by mouth can be absorbed and used by the body.
What is an example of bioavailability? ›
When a medicine is given orally, only part of the administered dose appears in the plasma. (Example: if 100 mg of a medicine are administered orally and 70 mg of this medicine are absorbed unchanged, the bioavailability is 0.7 or seventy percent).
What are the two methods to measure bioavailability? ›
It depends on pharmaceutical, patient, and route of administration factors. There are two main methods to measure bioavailability - pharmaco*kinetic and pharmacodynamic. Pharmaco*kinetic methods include plasma level time studies and urinary excretion studies which analyze parameters like Cmax, Tmax, and AUC.
What is absolute bioavailability and relative bioavailability? ›
"Absolute" bioavailability compares one non-IV route with IV administration. "Relative" bioavailability compares one non-IV route or formulation with another (instead of using IV route as a reference).
What are the two types of drug absorption? ›
Types
- Instantaneous absorption: absorption is nearly immediate. A common example is bolus intravenous injection.
- Zero-order absorption: rate of absorption is constant. ...
- First-order absorption: rate of absorption is proportional to the amount of drug remaining to be absorbed.
Bioavailability is referred to as the extent and rate to which the active drug ingredient or active moiety from the drug product is absorbed and becomes available at the site of drug action. The relative bioavailability in terms of the rate and extent of drug absorption is considered predictive of clinical outcomes.
