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To develop a dose dependent version of BCS and identify a critical dose after which the amount absorbed is independent from the dose.

We utilized a mathematical model of drug absorption in order to produce simulations of the fraction of dose absorbed (F) and the amount absorbed as function of the dose for the various classes of BCS and the marginal cases in between classes.

Simulations based on the mathematical model of F versus dose produced patterns of a constant F throughout a wide range of doses for drugs of Classes I, II and III, justifying biowaiver claim. For Classes I and III the pattern of a constant F stops at a critical dose Dose_cr after which the amount of drug absorbed, is independent from the dose. For doses higher than Dose_cr, Class I drugs become Class II and Class III drugs become Class IV. Dose_cr was used to define an in vivo effective solubility as S_eff = Dose_cr/250 ml. Literature data were used to support our simulation results.

A new biopharmaceutic classification of drugs is proposed, based on F, separating drugs into three regions, taking into account the dose, and Dose_cr, while the regions for claiming biowaiver are clearly defined.