WEEK 6: ABSORPTION , DISTRIBUTION AND ELIMINATION OF A DRUG Flashcards
What is pharmacokinetics?
What the body does to the drug?
State the 4 components of pharmacokinetics.
ABSORPTION, DISTRIBUTION, METABOLISM, EXCRETION
What is absorption?
ABSORPTION
The transfer of the drug from the site of administration to the bloodstream.
OUTLINE ROUTES BY WHICH DRUGS TRAVERSE CELL
MEMBRANES.
Simple diffusion
Facilitative diffusion
Active transport
Endocytosis
OUTLINE FACTORS INFLUENCING DRUG ABSORPTION
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
What is bioavailability of a drug?
Bioavailability is the fraction of administered drug that
reaches the systemic circulation.
For intravenous (IV) dosages, what is the bioavailability
assumed to be?
a) 0%
b) 25%
c) 50%
d) 75%
e) 100
E
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
C
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
What is distribution?
DISTRIBUTION
Entry of drug into the interstitial and tissues
OUTLINE FACTORS AFFECTING DISTRIBUTION.
Lipid solubility & molecular size
Blood flow & perfusion rate of the tissue
Capillary permeability
Protein binding capacity of the drug
What is volume of distribution?
VOLUME OF DISTRIBUTION
Hypothetical volume of fluid into which a drug is dispersed.
What is the volume of distribution in:
1.Blood
2.ECF
3.TBW
Blood (4L)
ECF (12-14L)
TBW (40-42L)
What is metabolism?
The chemical alteration of a drug.
The process of metabolism transforms lipophilic
drugs into more polar readily excretable products.
What is the primary site for drug metabolism?
The liver is the primary site of drug metabolism.
Biotransformation reactions are classically divided
into.
State the 2 types.
Biotransformation reactions are classically divided
into Phase I and Phase 2 reactions.
State the 3 phase 1 reactions.
PHASE 1 REACTION REACTIONS
- Oxidation
- Reduction
- Hydrolysis
State the phase 2 reactions.
- Glucuronidation
- Sulfation
- Acetylation
- Glutathione conjugation
- Methylation
Which of the following is a phase 1 drug metabolism
reaction?
a) Acetylation
b) Glucuronidation
c) Oxidation
d) Sulfation
C
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
C
Which of the following is a phase 1 drug metabolism
reaction?
a) Acetylation
b) Glucuronidation
c) Oxidation
d) Sulfation
C
Which of the following is a Phase II reaction?
a) Glucuronidation
b) Reduction
c) Oxidation
d) Hydrolysis
A
What is the main excretory organ?
Kidney is the main excretory organ.
What is half life?
State the formula for half life.
Half-life is the time required for the serum concentration to be reduced by 50%.
Half-life = 0.7 X Volume of distribution / Clearance
What is loading dose?
State the formula for calculating loading dose.
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
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.
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
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
