In common usage, the rate of absorption of an active ingredient or its
therapeutic moiety is generally not mentioned in the context of bioav
ailability. In this communication it is shown that exclusion of the ra
te of absorption may have serious consequence on the interpretation of
bioavailability depending on the underlying model for the system unde
r study. In the case of endogenous substances, the term ''bioavailabil
ity'' is ambiguous unless one specifies whether it refers to availabil
ity of the exogenous substance only or the sum total of the exogenous
and endogenous substances.