pharmacokinetics

Question 1

define Pharmacokinetics

Answer 1

– “what the body does to a drug”• The study of the absorption, distribution,
biotransformation and elimination of drugs.

Question 2

define Pharmacodynamics

Answer 2

– “what the drug does to the body
• The study of the biochemical and
physiological effect of the drugs as well as
their mechanism of action.
• Drugs do not create new cellular functions.
They alter the existing cellular functions.
• For example: A laxative increases the
peristaltic movement of the intestine

Question 3

Drugs can act by:

Answer 3

– combining with a small molecule (e.g.
antacids neutralize gastric acid),
– producing an alteration of cell membrane
activity (e.g. local anesthetics)
– or combining with receptors (e.g. atropine
reduces the rate of salivation by interacting
with receptors on salivary glands).
– act on DNA

Question 4

what are the Four phases of pharmacokinetics

Answer 4

– Absorption
– Distribution
– Bio-transformation/Metabolism
– Elimination

Question 5

Absorption phase

Answer 5

IV doesnt go through this process as it goes straight to blood stream.
- bioavailability: Sites of absorption in the gastrointestinal tract:
• Mouth
• Stomach
• Intestine
• Colon and rectum
(The most effective area of absorption in the gastrointestinal tract is the small intestine)

Question 6

Distribution phase

Answer 6

The process by which a drug is carried from its
absorption site to its action site.
• Organs such as the heart, liver, kidneys and brain will
receive the drug quickly as they have an extensive blood
supply. Whereas muscle, fat and skin have a less
extensive blood supply and receive the drug more slowly

Question 7

problems with Plasma proteins:

Answer 7

– A drug cannot provide pharmacological effect while it is bound
to a plasma protein as it cannot enter the cell. Only drugs that
are not bound to the plasma proteins can enter the cell.
– When two drugs are administered at the same time they may
compete to bind with the plasma protein. The drug that is not
bound to the plasma protein will provide pharmacological effect.
Some increase with age.

Question 8

what is Blood-brain barrier

Answer 8

– Only lipophilic drugs or drugs that can be taken up by active
transport can cross the blood-brain barrier.
– Meningitis can affect the blood-brain barrier and make it more
permeable so that medications that would normally not be able
to cross the barrier can

Question 9

biotransformation phase

Answer 9

For the drug to be eliminated by the body it needs to be watersoluble
so it can be excreted by the kidneys. This also gives the body
a chance to deactivate a drug before it accumulates and can become
toxic to the person.
• There are two phases of biotransformation:
– Phase 1: oxidation, reduction or hydrolysis of the drug.
– Phase 2: conjugation. Chemicals are added to the drug or
metabolite to make it more water-soluble.
• Most biotransformation occurs in the liver. The drug is
metabolised by liver enzymes known as microsomal enzymes.
The drug is converted to a metabolite.

Question 10

first pass metabolism

Answer 10

The drug is absorbed from the GI tract and passes
via the portal vein into the liver where some drugs
are metabolised. Sometimes the result of first pass
metabolism means that only a proportion of the
drug reaches the circulation.
• First pass metabolism can occur in the gut and the
liver

Question 11

bypass metabolism

Answer 11

Two ways to bypass first pass metabolism involve
giving the drug by sublingual and buccal routes.
• The drugs are absorbed by the oral mucosa in both
methods. In sublingual administration the drug is put
under the tongue where it dissolves in salivary
secretions. Nitroglycerine is administered in this way.
• In buccal administration the drug is placed between
the teeth and the mucous membrane of the cheek.
• Sublingual and buccal methods both avoid destruction
by the GI fluids and first pass effect of the liver

Question 12

Elimination phase

Answer 12

• Drugs can be eliminated via:
– Kidneys (as urine)
– Intestine (as faeces)
– Respiratory tract (as expired air)
– Lactiferous ducts (Breast milk)
– Salivary glands (as saliva)
– Sweat glands (as perspiration/sweat)

• The kidneys eliminate drugs by two different processes:
– Glomerular filtration
– Tubular secretion

Question 13

Glomerular filtration:

Answer 13

the drug is filtered through the
glomerulus into the renal tubule. The drug may be
partially reabsorbed into the bloodstream through the
wall of the tubule -> delaying full elimination from the
body.

Question 14

Tubular secretion:

Answer 14

the drug is secreted through the walls
of the tubule. This process is more rapid than glomerular
filtration and provides rapid elimination from the body

Question 15

what is drug half life

Answer 15

– The time interval needed for half of the amount of drug
to be eliminated to reduce the drug concentration in the
body.
– For example: if the half-life of a drug is 2 hours;
– Amount of drug in the body:
• At time of administration: 100%
• After 2 hours 50%
• After 4 hours 25%
• After 6 hours 12.5%
• After 8 hours 6.25%

Question 16

therapeutic window

Answer 16

The level of drug in the body that produces the best therapeutic effect.

Question 17

peak plasma level.

Answer 17

The amount of drug in the bloodstream increases as it is
being absorbed from the gastrointestinal tract. The level
continues to rise until the level of elimination is equal to
the absorption rate, this point is called the peak plasma
level.
• The peak plasma level is when the highest amount of
drug in the bloodstream is achieved from a single dose of
medication. Then the levels in the bloodstream will
decrease as the drug is eliminated from the body.

Question 18

Lock and Key Theory

Answer 18

• Drugs that fit into the receptor will be able to provide an
effect, whereas a drug that doesn’t fit correctly will have
a minimal effect or no effect at all.

Question 19

agnosit

Answer 19

drugs that fit into the receptor to provide a
pharmacological effect.
– Activates receptor
– Same response as endogenous “ligand” (natural
chemical in the body)

Question 20

antagonist

Answer 20

a drug that has no pharmacological effect butinteracts with the receptor to stop the action of theagonists.– Block endogenous “ligand”– Prevents the binding of the drug with the receptor –competes at the receptor– Most are reversible– Morphine is an agonist and provides a pharmacologicaleffect when it binds with the receptor. Naloxone is anantagonist and binds with the receptor to inhibit the actionor effect of Morphine

Question 21

Agonist-antagonist

Answer 21

: drugs that provide both some pharmacological effect as well as inhibiting.

Question 22

Drug toxicity:

Answer 22

this is when the level of the drug in the body exceeds the therapeutic range and becomes toxic
to the patient.

Question 23

Drug tolerance:

Answer 23

when a previously effective drug dosage no longer provides a therapeutic effect.