Transcript Tina said you all learned ALOT last week

You have learned
a LOT so far
A few extra facts to throw in
No single reproducible abnormality in any NT,
enzyme, receptor or gene has been found to
cause Psychopathology (but they can contribute
to the risk)
Virtually all Psychotropic drugs have been found
thru serendipity or by guessing
Finally, we need to know how…
Drugs effect the body
(Pharmacodynamics)
That the body effects the drugs
absorption, distribution, biotransformation,
and excretion (Pharmacokinetics)
Absorption
Occurs in the stomach and small intestines for
oral medications
Bioavailability- How much of the drug is
available in the bloodstream
– Taken with or without food
– Blood/Brain Barrier
– Introvenious drugs (100% bioavailable)
Why is this necessary to know?
Distribution
After the drug is absorbed and reaches the blood stream
(absorption)….
Then it must be distributed to various organs or body
sites
– High blood flow 1st (liver, kidney, heart, brain)
– Muscles and fat tissues 2nd
Each medication has a particular distribution pattern.
– For example, TCAs are distributed in the fat and muscle cells.
What are the implications for the prescribing physician?
– Why might a patient not become depressed for days or weeks
after discontinuing medications?
Biotransformation (Metabolism)
Toxicity Issues
Metabolizes primarily in the Liver via
enzymes, so that Kidneys can secrete
more easily
Different people have different enzymes in
the liver, thus one may metabolize Zoloft
well, but not Prozac.
What are the implications for prescribing
physicians?
Biotransformation
What do you think are the cultural
implications in Biotransformation?
Biotransformation
5-10% of Caucasians are poor metabolizers via
the enzyme CYP450 2D6, so they must
metabolize drugs that require this enzyme in an
alternate manner, which might not be as efficient
20% of Japanese and Chinese individuals have
reduced activity in enzyme CYP450 2C19
How does this make you feel about the clinical
studies that have been done with little attention
to race/ethnicity?
Excretion
Drugs are eliminated from the
body thru the Kidneys, Intestines,
Respiratory, Sweat, Saliva, and
Breast Milk
Adequate excretion is dependent
on Kidney functioning
What should physicians take into
consideration prior to prescribing a
medication?
Half-Life is an important factor in
Excretion
Half-life: The period of time required for the
concentration or amount of drug in the body to be
reduced by one-half
4-5 X half-life=Steady State
– As repeated doses of a drug are administered its plasma
concentration builds up and reaches what is known as a steady
state. This is when the amount of drug in the plasma has built up
to a concentration level that is therapeutically effective and as
long as regular doses are administered to balance the amount of
drug being cleared the drug will continue to be active. The time
taken to reach the steady state is about five times the half life of
a drug.
Steady State does not = onset of drug action
Half-life example
Some drugs like ibuprofen have very short half
lives, others take much longer to eliminate from
the plasma resulting in a long half life. So drugs
like ibuprofen that are cleared from the blood
more rapidly than others need to be given in
regular doses to build up and maintain a high
enough concentration in the blood to be
therapeutically effective.
Now that we understand
Pharmacokinetics, we
want to know more about
Pharmacodynamics-how
and which the drugs
effect the body. This will
be the focus of the rest of
the class