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0:00
Welcome to this short
lecture on bioavailability,
absorption, and distribution.
I'm Karel Allegaert,
Clinical Pharmacologist
working at KU Leuven
in Belgium as well as
Erasmus University of
Rotterdam in the Netherlands.
0:17
Why are we discussing
this topic?
Well, it is because absorption
as well as distribution
are two of the four parameters
crucial to determine
pharmacokinetics.
Absorption, distribution,
metabolism,
and excretion will drive the
concentration/time profile.
We will focus on these
first two parameters in
this short lecture and
other information on
metabolism and excretion will
be provided in another lecture.
0:46
Let's go first to
some definitions.
If we consider bioavailability
commonly used with a big F,
it relates to the fraction
of an administered drug that
gains access to the
systemic circulation,
so by definition, it is
between zero and 100.
Absolute values refer to
the area under the curve
obtained after a given dose is
provided by intravenous route.
Relative bioavailability
refers to when you compare
two different formulations or
two different routes
of administration,
for instance, oral tablet
versus oral syrup,
or oral tablet versus
subcutaneous administration.
1:28
Absorption in itself is by
definition, the
passage of a drug
from its site of administration
to its site of action
and to do so, it will have
to cross cell membranes.
Except for IV administration,
the drug will have to be
transported from the initial
site of the administration,
for instance,
subcutaneous, oral,
sublingual, and will
have to make it
into the systemic/blood
circulation.
However, we should realize that
the systemic circulation
itself is not always the site
of action for a given
drug for instance
for analgesic or
seizures it's in general
the central nervous
system that you target.
For chemotherapy, it
could be in the blood
if it is, for instance, leukemia
but it can also be
located in other tissues.
For instance, for infections,
if you have a
subcutaneous infection,
it's nice to have an
antibiotic in your circulation
but it will have to make it to
the subcutaneous tissues
to be effective.
