Biopharmaceutics Classification System

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

This system is a guidance for predicting the intestinal drug absorption provided by the U.S. Food and Drug Administration ^*. 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) apperature. 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 criterias can be applied.
Class IV - Low Permeability, Low Solubility
- Example: Hydrochlorothiazide
- Those compounds have a poor bioavailability. Usually they are not good absorbed over the intestinal mucosa and a high variability is expected.

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

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