WEEK 6: ABSORPTION , DISTRIBUTION AND ELIMINATION OF A DRUG

Question 1

What is pharmacokinetics?

Answer 1

What the body does to the drug?

Question 2

State the 4 components of pharmacokinetics.

Answer 2

ABSORPTION, DISTRIBUTION, METABOLISM, EXCRETION

Question 3

What is absorption?

Answer 3

ABSORPTION
The transfer of the drug from the site of administration to the bloodstream.

Question 4

OUTLINE ROUTES BY WHICH DRUGS TRAVERSE CELL
MEMBRANES.

Answer 4

 Simple diffusion
 Facilitative diffusion
 Active transport
 Endocytosis

Question 5

OUTLINE FACTORS INFLUENCING DRUG ABSORPTION

Answer 5

 PH: Most drugs are either weak acids or weak bases.
 Blood flow to the absorption site:
 Total surface area available for absorption
 Contact time at the absorption surface

Question 6

What is bioavailability of a drug?

Answer 6

Bioavailability is the fraction of administered drug that
reaches the systemic circulation.

Question 7

For intravenous (IV) dosages, what is the bioavailability
assumed to be?
a) 0%
b) 25%
c) 50%
d) 75%
e) 100

Answer 7

E

Question 8

Experimental evaluation of the pharmacokinetics of a
drug under development leads to the finding that it
“Undergoes significant first pass hepatic metabolism.”

Which of the following administration routes was most likely used to reach this conclusion?

a) Intramuscular
b) Intravenous
c) Oral
d) Rectal
e) Sublingual

Answer 8

C

Question 9

We are conducting pharmacokinetic studies on a new drug that we hope will be approved for clinical use. We
insert a venous catheter to sample blood at various times
after drug administration and take a sample for the immediate predrug blood level of the drug
(Which should be zero). After assaying the blood samples for the drug, we make a graph that plots serum drug concentrations over time, continuing until tests reveal blood levels as undetectable.

Which of the following is calculated as the ratio of the area under the curve (AUC) obtained by oral administration vs. the AUC for intravenous administration of the same drug?

a) Absorption
b) Bioavailability
c) Clearance
d) Elimination rate constant
e) Volume of distribution

Question 10

What is distribution?

Answer 10

DISTRIBUTION
Entry of drug into the interstitial and tissues

Question 11

OUTLINE FACTORS AFFECTING DISTRIBUTION.

Answer 11

 Lipid solubility & molecular size
 Blood flow & perfusion rate of the tissue
 Capillary permeability
 Protein binding capacity of the drug

Question 12

What is volume of distribution?

Answer 12

VOLUME OF DISTRIBUTION
 Hypothetical volume of fluid into which a drug is dispersed.

Question 13

What is the volume of distribution in:
1.Blood
2.ECF
3.TBW

Answer 13

Blood (4L)
ECF (12-14L)
TBW (40-42L)

Question 14

What is metabolism?

Answer 14

The chemical alteration of a drug.

 The process of metabolism transforms lipophilic
drugs into more polar readily excretable products.

Question 15

What is the primary site for drug metabolism?

Answer 15

The liver is the primary site of drug metabolism.

Question 16

Biotransformation reactions are classically divided
into.
State the 2 types.

Answer 16

Biotransformation reactions are classically divided
into Phase I and Phase 2 reactions.

Question 17

State the 3 phase 1 reactions.

Answer 17

PHASE 1 REACTION REACTIONS

• Oxidation
• Reduction
• Hydrolysis

Question 18

State the phase 2 reactions.

Answer 18

• Glucuronidation
• Sulfation
• Acetylation
• Glutathione conjugation
• Methylation

Question 19

Which of the following is a phase 1 drug metabolism
reaction?
a) Acetylation
b) Glucuronidation
c) Oxidation
d) Sulfation

Answer 19

C

Question 20

Conjugation is …

a) A) process of drug reduction by special enzymes
b) B) process of drug oxidation by special enzymes
c) C) coupling of a drug with an endogenous substrate

Answer 20

C

Question 21

Which of the following is a phase 1 drug metabolism
reaction?
a) Acetylation
b) Glucuronidation
c) Oxidation
d) Sulfation

Answer 21

C

Question 22

Which of the following is a Phase II reaction?
a) Glucuronidation
b) Reduction
c) Oxidation
d) Hydrolysis

Answer 22

A

Question 23

What is the main excretory organ?

Answer 23

Kidney is the main excretory organ.

Question 24

What is half life?
State the formula for half life.

Answer 24

Half-life is the time required for the serum concentration to be reduced by 50%.

Half-life = 0.7 X Volume of distribution / Clearance

Question 25

What is loading dose?

State the formula for calculating loading dose.

Answer 25

The loading dose is the is the initial higher dose of the
drug given at the start of treatment, to rapidly achieve the desired therapeutic concentration.

Loading dose = Volume of distribution X desired therapeutic plasma concentration

Question 26

Drugs showing zero-order kinetics of elimination:
a) Are more common than those showing first-order
kinetics.
b) Decrease in concentration exponentially with time.
c) Have a half-life independent of dose.
d) Show a plot of drug concentration versus time
that is linear.
e) Show a constant fraction of the drug eliminated per unit
of time.

Question 27

A patient was given a 160-mg dose of a drug IV, and 80 mg was eliminated during the first 120 minutes. If the drug
follows first-order elimination kinetics, how much
of the drug will remain 6 hours after administration?
A. 0 mg
B. 10mg
C. 20mg
D. 40mg
E. 60m

Question 28

In a patient weighing 70kg, acetaminophen has a Vd = 70L
and Cl =350mL/min.

The elimination half-life of the drug is approximately…

a) 35 min
b) 70 min
c) 140 min
d) 210 min
e) 280 min