The Biopharmaceutics Classification System is a guidance for predicting the intestinal drug absorption provided by the U.S. Food and Drug Administration [1]. The fundamental basis for the BCS was established by Dr. Gordon Amidon who was presented with a Distinguished Science Award at the August 2006 International Pharmaceutical Federation (FIP) congress in Salvador, Brazil.^{[citation needed]}

This system allows to restrict 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, since 85% of the most sold drugs in the USA and Europe are orally administered.

According to the Biopharmaceutics Classification System (BCS (disambiguation)), drug substances are classified as follows:

• 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
  • Example: Glibenclamide
  • 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: Hydrochlorothiazide
  • 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 250ml or less of aqueous media over the ph range of 1 to 7.5. The volume estimate of 250ml 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 prediction the drug absorption systems capable of predicting the 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 and intravenous dose.
3. Dissolution class boundaries- An immediate release products is considered rapidly dissolving when no less than 85% of the labeled amount of the drug substance dissolve within 30 minutes using USP Dissolution Apparatus 1 at 100 RPM or Apparatus 2 at 50 RPM in a volume of 900ml or less in following media,) 0.1 N HCl or simulated gastric fluid or pH 4.5 buffer and pH 6.8 buffer or simulated intestinal fluid.

[edit] See also

• ADME
  • Partition coefficient
  • Bioavailability
  • Drug metabolism
  • First pass effect
• Polar surface area
• IVIVC

[edit] References

• H. Waterbeemd, H. Lennernäs, P. Artursson (editors), Drug bioavailability: estimation of solubility, permeability, absorption and bioavailability, Wiley-VCH, Weinheim, Germany, 2003. ISBN 3-527-30438-X

• Amidon, G. L.; Lennernas, H.; Shah, V. P.; Crison, J. R. (1995). A Theoretical Basis for a

Biopharmaceutic Drug Classification: The Correlation of In Vitro Drug Product Dissolution and In Vivo Bioavailability. Pharm. Res. 12: 413–420.

[edit] External links

• BCS guidance of the U.S. Food and Drug Administration

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