Study Set Content:
For an intravenous dose of the drug, bioavailability
is assumed to be equal to
unity (100%).
For a drug administered orally, bioavailability may
be less than 100% for two main reasons:
incomplete extent of absorption across the gut
wall
first-pass elimination by the liver
After oral administration, a drug may be
incompletely absorbed, eg, only 70% of a dose of
digoxin reaches the systemic circulation.
This is mainly due to
lack of absorption from the
gut.
Other drugs are either too
hydrophilic, lipophilic
is an intestinal enzyme which is part of the
cytochrome P4150 metabolic system.
CYP3A4
is important
in many drug-drug and drug-food interactions, it is one of
the first enzymes to break down medications when they
enter the body.
CYP3A4
According to studies, (blank) demonstrated to inhibit
the function of CYP3A4 and its effect on metabolism of a
number of drugs.
grapefruit juice
Because it takes the grapefruit juice
approximately (blank) to leave the body so taking medication
at a different time of the day is not an adequate solution to
avoid this problem.
1 day
Because it takes the grapefruit juice
approximately 1 day to leave the body so taking medication
at a different time of the day is not an adequate solution to
avoid this problem. This can lead to (blank) as the
medication concentration is increased.
adverse reaction
Drugs affected by this are
SSRI’s, SNRI’s,
benzodiazepines, sedatives, and other centrally active
drugs.
CYP3A4 helps metabolize these drugs in the small
intestine and if (blank) is consumed it blocks the
action of CYP3A4. Therefore, instead of being metabolized
more of these drugs enters the blood and stays in the body
longer and the result will be too much drugs in the body.
grapefruit juice
Following absorption across the gut wall, the portal
blood delivers the drug to the (blank) prior to entry into
the systemic circulation.
liver
is when the concentration of the
drug is greatly reduced before reaching the systemic
circulation
First-pass elimination
Metabolism can occur:
Gut wall + Portal blood +
Liver
In addition, the liver can excrete the drug into
the
bile
First pass elimination or also known as
pre-systemic
elimination
First pass elimination or also known as pre-systemic
elimination occurs when the drugs are given orally. A
portion of the drug is eliminated before it goes to the
systemic absorption.
How to obtain better systemic absorption of drug that
has high first-pass effects?
o Dose should be
increased
Alternative route aside from
oral
Modify its (blank) (delayed release like
enteric coated aspirin) so that drugs can be
absorbed more in the GIT.
dosage form
