The in vivo disintegration, dissolution, absorption, and disposition processes of ampicillin products are separated by means of moment analysis. This method is model‐independent, that is, any specific model is not assumed. The mean residence time (MRT), mean absorption time (MAT), mean dissolution time (MDT), and mean disintegration time (MDIT) are calculated for several dosage forms of ampicillin. The fraction of dose absorbed (F) is also separated into several fractions corresponding to these in vivo processes. Bioavailability and bioequivalence are discussed in terms of the zero and first moments. The flip‐flop behavior of ampicillin is proved by the fact that the MRT following intravenous injection is less than the MAT of any oral dosage form. Absorption of released ampicillin is proved to be a rate‐determining step, since the MRT of released ampicillin in the GI tract is the greatest of all MRT corresponding to the in vivo processes. Moment analysis is compared with classical compartment theory, and a new component concept is introduced.
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