Pharmacokinetics

Question 1

What must happen before drug absorption?

Answer 1

Administration

Question 2

What is drug absorption?

Answer 2

The passage of a drug from the site of administration into the bloodstream.
The faster the drug crosses the membrane, the better the drug absorption.
Determining how much of the drug gets into the bloodstream.

Question 3

What must the drug cross to get absorbed in the body?

Answer 3

cellular barriers, specifically lipid membranes.

Question 4

What is simple(passive) diffusion in drug absorption?

Answer 4

Drug moves from an area of high concentration to an area of lower concentration through a semi-permeable membrane.

Question 5

What are the main factors determining the rate of passive diffusion?

Answer 5

lipid solubility
concentration gradient

Question 6

What are the properties of carriers in facilitated diffusion?

Answer 6

Carriers are selective
saturable
do not require energy

Question 7

What facilitated diffusion in drug absorption?

Answer 7

Drug moves by binding to carriers and moves from high concentration to a low concentration.

Question 8

What is Pharmacokinetics?

Answer 8

The study of effect of living systems or the body on drugs.

Question 9

What are the four main processes involved in pharmacokinetics?

Answer 9

Absorption
Distribution
Metabolism
Excretion

Question 10

What is active transport in drug adsorption?

Answer 10

Drugs move by binding to specific carriers and can move against a concentration gradient

Question 11

What are the properties of carries in active transport?

Answer 11

Carries are selective
saturable
need energy

Question 12

What is endocytosis in drug absorption?

Answer 12

Engulfment of the drug by the cell membrane
Transported into the cell by pinching off a drug-filled vesicle.
needs energy

Question 13

What factors influence drug absorption?

Answer 13

1.Effect of pH on the drug
2. Blood flow to the absorption site
3. Total surface area available for absorption
4. Rate of gastric emptying

Question 14

How does pH affect drug absorption?

Answer 14

Acidic drugs are better absorbed in an acidic environment (e.g., stomach).
Alkaline drugs are better absorbed in an alkaline environment (e.g., intestines).
The state of ionization (charge) determined by pH affects absorption, with uncharged/non-ionized drugs diffusing across lipid membranes more readily.

Question 15

How does blood flow to the absorption site affect drug absorption?

Answer 15

Higher blood flow to a specific site increases absorption. For example, the intestines have higher blood flow compared to the stomach, making absorption more efficient in the intestines.

Question 16

How does the total surface area available for absorption affect absorption?

Answer 16

Higher surface area of absorption site leads to more absorption. For example, the intestine has a surface area 1000 times greater than the stomach, making absorption more efficient in the intestine.

Question 17

What is gastric emptying and how does it affect the drug absorption?

Answer 17

The rate of gastric emptying is how quickly stomach contents move to the small intestines.
It is affected by various factors such as drugs (e.g., metoclopramide speeds up gastric emptying) and viral infections.

Question 18

What is bioavailability?

Answer 18

The fraction of the ingested dose of a drug that gains access to the systemic circulation.

Question 19

What is drug distribution?

Answer 19

Reversible transfer of a drug between the blood and extravascular fluids and tissues of the body. (e.g. fat, muscle, brain)

Question 20

where are lipid insoluble drugs mainly confined?

Answer 20

plasma and interstitial fluid

Question 20

What factors affect drug distribution?

Answer 20

Regional blood flow
Capillary permeability
Drug properties (lipophilicity, volume of distribution, binding to plasma protein)

Question 21

where do lipid soluble drugs distribute?

Answer 21

they reach all compartments and may accumulate fat

Question 22

what is volume distribution?

Answer 22

the proportionality factor between the amount of drug in the body and the amount of drug in the plasma

Question 23

what are the major compartments for drug distribution?

Answer 23

Plasma (5% of body weight)
Interstitial fluid (16%)
Intracellular fluid (35%)
Transcellular fluid (2%)
Fat (20%)

Question 23

what types of drugs are mainly confined to the plasma compartment?

Answer 23

lipid-insoluble, large molecular weight, and highly protein-bound drugs (e.g. heparin)

Question 24

what types of drugs pass into the interstitial fluid?

Answer 24

drugs with low molecular weight and hydrophilic properties (e.g. gentamicin)

Question 25

what types of drugs move into the intracellular fluid?

Answer 25

drugs with low molecular weight and lipophilic properties (e.g. ethanol)

Question 26

What is drug metabolism?

Answer 26

chemical alterations in the drug structure by specific enzymatic processes in the body(biotransformation)

Question 27

what are the objectives of drug metabolism?

Answer 27

Transform lipophilic drugs into more polar, readily excretable products.
Produce drug metabolites that are more ionized and easily excreted.

Question 28

where can drug metabolism occur?

Answer 28

liver (main site)
kidneys
muscle tissue
intestinal wall
lungs
skin
blood

Question 28

what reactions are involved in phase 1 metabolism?

Answer 28

oxidation, reduction and hydrolysis reactions

Question 29

what is first pass metabolism?

Answer 29

the process where an orally administered drug enters the liver and undergoes extensive biotransformation, reducing its bioavailability

Question 29

what reactions are involved in phase 2 metabolism?

Answer 29

conjugation reactions, glucuronidation, acetylation and sulfation.

Question 30

what is enterohepatic circulation?

Answer 30

some conjugated drug products are excreted via bile, reactivated in the intestine by bacteria and the reabsorbed.

Question 31

what is drug excretion?

Answer 31

the process whereby drugs or metabolites are irreversibly transferred from the internal to external environment through renal or non-renal routes.

Question 31

what are the types of drug excretion?

Answer 31

renal excretion
biliary excretion
pulmonary excretion
salivary excretion
mammary excretion
skin/dermal excretion
gastrointestinal excretion

Question 31

what is the half-life (t1/2) of a drug?

Answer 31

The time taken for the concentration of a drug to decrease to half (50%) of its starting dose in the body.

Question 32

why is the half-life of a drug important?

Answer 32

it helps determine how frequently a drug should be administered, as different drugs have different half-lives.

Question 33

what is first-order kinetics?

Answer 33

A chemical reaction where the rate of elimination is directly proportional to the concentration of the drug?

Question 34

what is the onset of action?

Answer 34

the time interval from when the drug is administered to when its therapeutic effects begin

Question 34

what is zero-order kinetics?

Answer 34

drugs undergo constant elimination regardless of the plasma concentration

Question 35

what is the duration of action?

Answer 35

the length of time that a drug produces its therapeutic effect

Question 36

what is the peak effect?

Answer 36

the maximum concentration of a drug that is reached in the body

Question 37

what is the therapeutic index?

Answer 37

the ratio of the dose that exerts a toxic effect in 50% of the population (TD50) to the dose of a drug that exerts a therapeutic/ effective response (ED50) to 50% in the population (TI=TD50/ED50)

Question 38

What does the therapeutic index represent?

Answer 38

It represents the safety margin of a drug for clinical use. A higher therapeutic index is better, indicating a wide margin between effective and toxic doses. Drugs with a narrow therapeutic index have a higher risk for toxicity.