Biopharmaceutics Classification System

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

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

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.

Alternatively non-human systems capable of predicting drug absorption in humans can be used (such as in-vitro culture methods).