Bioavailability

In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation.[1]

By definition, when a medication is administered intravenously, its bioavailability is 100%.[2][3] However, when a medication is administered via routes other than intravenous, its bioavailability is lower due to intestinal epithelium absorption and first-pass metabolism. Thereby, mathematically, bioavailability equals the ratio of comparing the area under the plasma drug concentration curve versus time (AUC) for the extravascular formulation to the AUC for the intravascular formulation.[4] AUC is used because AUC is proportional to the dose that has entered the systemic circulation.[5]

Bioavailability of a drug is an average value; to take population variability into account, deviation range is shown as ±.[4] To ensure that the drug taker who has poor absorption is dosed appropriately, the bottom value of the deviation range is employed to represent real bioavailability and to calculate the drug dose needed for the drug taker to achieve systemic concentrations similar to the intravenous formulation.[4] To dose without knowing the drug taker's absorption rate, the bottom value of the deviation range is used in order to ensure the intended efficacy, unless the drug is associated with a narrow therapeutic window.[4]

For dietary supplements, herbs and other nutrients in which the route of administration is nearly always oral, bioavailability generally designates simply the quantity or fraction of the ingested dose that is absorbed.[6][7][8]

  1. ^ Hebert, Mary F. (2013). "Impact of Pregnancy on Maternal Pharmacokinetics of Medications". Clinical Pharmacology During Pregnancy. Elsevier. pp. 17–39. doi:10.1016/b978-0-12-386007-1.00003-9. ISBN 978-0-12-386007-1.
  2. ^ Griffin, J. P. (7 December 2009). The Textbook of Pharmaceutical Medicine (6th ed.). Jersey: BMJ Books. ISBN 978-1-4051-8035-1.[page needed]
  3. ^ Flynn, Edward (2007). "Pharmacokinetic Parameters". xPharm: The Comprehensive Pharmacology Reference. Elsevier. pp. 1–3. doi:10.1016/b978-008055232-3.60034-0. ISBN 978-0-08-055232-3.
  4. ^ a b c d Davis, Jennifer L. (2018). "Pharmacologic Principles". Equine Internal Medicine. Elsevier. pp. 79–137. doi:10.1016/b978-0-323-44329-6.00002-4. ISBN 978-0-323-44329-6.
  5. ^ Johanson, G. (2010). "Modeling of Disposition". Comprehensive Toxicology. Elsevier. pp. 153–177. doi:10.1016/b978-0-08-046884-6.00108-1. ISBN 978-0-08-046884-6.
  6. ^ Heaney, Robert P. (2001). "Factors Influencing the Measurement of Bioavailability, Taking Calcium as a Model". The Journal of Nutrition. 131 (4): 1344S–8S. doi:10.1093/jn/131.4.1344S. PMID 11285351.
  7. ^ SANDSTEAD, HAROLD H.; AU, WILLIAM (2007). "Zinc**Dr. Carl-Gustaf Elinder was the author of this chapter in the 2nd edition of the Handbook on Toxicology of Metals; his text provided guidance.". Handbook on the Toxicology of Metals. Elsevier. pp. 925–947. doi:10.1016/b978-012369413-3/50102-6. ISBN 978-0-12-369413-3. Bioavailability is the major factor affecting dietary requirements (Sandstrom, 1997). Flesh foods facilitate bioavailability, although indigestible Zn-binding ligands decrease bioavailability (Mills, 1985).
  8. ^ Solomons, N.W. (2003). "ZINC | Physiology". Encyclopedia of Food Sciences and Nutrition. Elsevier. pp. 6272–6277. doi:10.1016/b0-12-227055-x/01309-2. ISBN 978-0-12-227055-0. Bioavailability strictly refers to both the uptake and metabolic utilization of a nutrient.