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{{Short description|System to differentiate drugs on the basis of their solubility and permeability}}
{{other uses of|BCS}}
{{refimprove|date=July 2019}}
The '''Biopharmaceutics Classification System''' ('''BCS''') is a system to differentiate drugs on the basis of their solubility and permeability.<ref name = "Mehta_2016">{{cite book | last1 = Mehta | first1 = Mehul | name-list-style = vanc | title = Biopharmaceutics Classification System (BCS): Development, Implementation, and Growth | date = 2016 | publisher = Wiley | isbn = 978-1-118-47661-1 }}</ref>

This system restricts the prediction using the parameters [[solubility]] and [[intestinal permeability]]. The solubility classification is based on a [[United States Pharmacopoeia]] (USP) aperture. The intestinal permeability classification is based on a comparison to the [[Route of administration|intravenous injection]]. All those factors are highly important because 85% of the most sold drugs in the [[United States]] and [[Europe]] are [[route of administration|orally administered]].{{Citation needed|reason=While the number is often claimed, a citation is rarely given|date=October 2016}}

== Classes ==
[[File:Biopharmaceutics Classification System (BCS).jpg|thumb|400px|BCS classes]]
According to the Biopharmaceutics Classification System (BCS) drug substances are classified to four classes upon their solubility and permeability:<ref name = "Mehta_2016"/>
* '''Class I – high [[intestinal permeability|permeability]], high [[solubility]] '''
** Example: [[metoprolol]], [[paracetamol]]<ref>{{cite web |url=https://www.ema.europa.eu/documents/scientific-guideline/draft-paracetamol-oral-use-immediate-release-formulations-product-specific-bioequivalence-guidance_en.pdf |title= Draft agreement |date=22 June 2017 |website=www.ema.europa.eu |format=PDF|access-date=2019-07-03}}</ref>
** Those compounds are well absorbed and their absorption rate is usually higher than excretion.
* '''Class II – high permeability, low solubility'''
** Example: [[glibenclamide]], [[bicalutamide]], [[ezetimibe]], [[aceclofenac]]
** The [[bioavailability]] of those products is limited by their solvation rate. A correlation between the ''[[in vivo]]'' bioavailability and the ''[[in vitro]]'' solvation can be found.
* '''Class III – low permeability, high solubility '''
** Example: [[cimetidine]]
** The absorption is limited by the permeation rate but the drug is solvated very fast. If the formulation does not change the permeability or gastro-intestinal duration time, then class I criteria can be applied.
* '''Class IV – low permeability, low solubility '''
** Example: [[bifonazole]]
** Those compounds have a poor bioavailability. Usually they are not well absorbed over the intestinal mucosa and a high variability is expected.

==Definitions==
The drugs are classified in BCS on the basis of solubility and permeability.

Solubility class boundaries are based on the highest dose strength of an immediate release product. A drug is considered highly soluble when the highest dose strength is soluble in 250 ml or less of aqueous media over the pH range of 1 to 6.8. The volume estimate of 250 ml is derived from typical [[bioequivalence]] study protocols that prescribe administration of a drug product to fasting human volunteers with a glass of water.

Permeability class boundaries are based indirectly on the extent of absorption of a drug substance in humans and directly on the measurement of rates of mass transfer across human intestinal membrane. Alternatively non-human systems capable of predicting drug absorption in humans can be used (such as in-vitro culture methods). A drug substance is considered highly permeable when the extent of absorption in humans is determined to be 85% or more of the administered dose based on a mass-balance determination or in comparison to an [[intravenous]] dose.

==See also==
* [[ADME]]
** [[Partition coefficient]]
** [[Bioavailability]]
** [[Drug metabolism]]
** [[First pass effect]]
* [[Polar surface area]]
* [[IVIVC]]

== References ==
{{Reflist}}

== Further reading ==
{{refbegin}}
* {{cite book | first1 = Gerd | last1 = Folkers | last2 = van de Waterbeemd | first2 = Han | last3 = Lennernäs | first3 = Hans | first4 = Per | last4 = Artursson | first5 = Raimund | last5 = Mannhold | first6 = Hugo | last6 = Kubinyi | name-list-style = vanc | title = Drug Bioavailability: Estimation of Solubility, Permeability, Absorption and Bioavailability (Methods and Principles in Medicinal Chemistry) | publisher = Wiley-VCH | location = Weinheim | year = 2003 | isbn = 3-527-30438-X | url = https://archive.org/details/drugbioavailabil0000unse | url-access = registration }}
* {{cite journal | vauthors = Amidon GL, Lennernäs H, Shah VP, Crison JR | title = A theoretical basis for a biopharmaceutic drug classification: the correlation of in vitro drug product dissolution and in vivo bioavailability | journal = Pharm. Res. | volume = 12 | issue = 3 | pages = 413–20 |date=March 1995 | pmid = 7617530 }}
{{refend}}

==External links==
* [https://web.archive.org/web/20120912010209/http://www.fda.gov/AboutFDA/CentersOffices/OfficeofMedicalProductsandTobacco/CDER/ucm128219.htm BCS guidance] of the [[U.S. Food and Drug Administration]]

[[Category:Pharmacological classification systems]]
[[Category:Pharmacy in the United States]]

Biopharmaceutics Classification System - Revision history

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