  A lot of criticism against the standard formulation of pharmacokinetics has
been raised by several authors. It seems that the natural reaction for that
criticism is to comment it from the point of view of the theory of conservation
laws. Simple example of balance equations for the intravenous administration of
drug has been given in 2011 and the corresponding equations for extravasal
administration are in the text. In principle, the equations of that kind allow
one to describe in the self consistent manner different processes of
administration, distribution, metabolism and elimination of drugs. Moreover, it
is possible to model different pharmacokinetic parameters of the
non-compartmental pharmacokinetics and therefore to comment criticism of
Rosigno. However, for practical purposes one needs approximate methods, in
particular, those based on separation of the time scales. In this text, such
method is described and its effectiveness is discussed. Basic equations are in
the next chapter. Final remarks are at the end of the text.
