Biopharmaceutics Classification System

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For other uses of the abbreviation BCS, see BCS (disambiguation).

The Biopharmaceutics Classification System is a system to differentiate the drugs on the basis of their solubility and permeability.[1]

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 intravenous injection. All those factors are highly important because 85% of the most sold drugs in the United States and Europe are orally administered.

BCS classes[edit]

According to the Biopharmaceutical Classification System (BCS) drug substances are classified to four classes upon their solubility and permeability:[1]

  • Class I - high permeability, high solubility
    • Example: metoprolol
    • Those compounds are well absorbed and their absorption rate is usually higher than excretion.
  • Class II - high permeability, low solubility
  • 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.

The drugs are classified in BCS on the basis of following parameters:
1. Solubility
2. Permeability
3. Dissolution

The class boundaries for these parameters are:

  1. Solubility class boundaries – It is 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 7.5. 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.
  2. Permeability class boundaries – It is 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 90% or more of the administered dose based on a mass-balance determination or in comparison to an intravenous dose.

  1. Dissolution class boundaries – An immediate release product is considered rapidly dissolving when no less than 85% of the labeled amount of the drug substance dissolves within 15 minutes using USP Dissolution Apparatus 1 at 100 RPM or Apparatus 2 at 50 RPM in a volume of 900 ml or less in the following media: 0.1 N HCl or simulated gastric fluid or pH 4.5 buffer and pH 6.8 buffer or simulated intestinal fluid.

See also[edit]


  1. ^ a b Mehta M (2016). Biopharmaceutics Classification System (BCS): Development, Implementation, and Growth. Wiley. ISBN 978-1-118-47661-1. 

Further reading[edit]

  • Folkers G, van de Waterbeemd H, Lennernäs H, Artursson P, Mannhold R, Kubinyi H (2003). Drug Bioavailability: Estimation of Solubility, Permeability, Absorption and Bioavailability (Methods and Principles in Medicinal Chemistry). Weinheim: Wiley-VCH. ISBN 3-527-30438-X. 
  • Amidon GL, Lennernäs H, Shah VP, Crison JR (March 1995). "A theoretical basis for a biopharmaceutic drug classification: the correlation of in vitro drug product dissolution and in vivo bioavailability". Pharm. Res. 12 (3): 413–20. PMID 7617530. 

External links[edit]