Study Set Content:
The effect of first-pass hepatic elimination on
bioavailability is expressed as the extraction ratio
ER = CL liver/Q
is the fraction of the drug that is
irreversibly removed by an organ or tissue as the
plasma containing drug perfuses that tissue.
extraction ratio
This
can be obtained by measuring the plasma drug
concentration (blank) the liver and the plasma drug
concentration (blank) the liver.
entering, exiting
where Q is
is hepatic blood flow,
systemic bioavailability of the drug
(F)
extent of absorption
f
extraction ratio
ER
F =
f X (1 – ER)
The rate of absorption describes the rate of drug into
the
central compartment
The rate of absorption is determined by the
site of
administration and the drug formulation.
Both the rate of absorption and the extent of input
can influence the (blank) of a drug.
clinical effectiveness
A drug will only take effect if it is already (blank)
by the body this determined by the properties of the
dosage forms, drugs, and manufacture.
absorbed
There are several reasons for different routes of
administration used in clinical medicine:
for
convenience
to (blank)concentration at the site of action and
minimize it elsewhere (eg, topical)
maximize
to prolong the duration of drug absorption (eg,
transdermal), or to avoid the
first-pass effect.
The hepatic first-pass effect can be avoided to a great
extent by use of (blank) and (blank) and to a lesser extent by use of (blank)
sublingual tablets, transdermal preparations, rectal suppositories
Sublingual absorption provides direct access to
(blank)—not portal—veins.
systemic
offers the same advantage.
transdermal route
Drugs absorbed from suppositories in the lower
rectum enter vessels that drain into the (blank) thus bypassing the liver.
inferior vena
cava,
However, suppositories tend to move upward in the
rectum into a region where veins that lead to the liver
predominate. Thus, only about (blank) of a rectal dose
can be assumed to bypass the liver.
50%
