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Pharmacokinetics > Pharmacokinetics - Absorption > Flashcards

Pharmacokinetics - Absorption Flashcards

1
Q

State different means of absorption from GI tract:

A

a. Passive Diffusion; b. Facilitated diffusion;

c. Active Transport; d. Endocytosis & Exocytosis

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2
Q

Definition of Absorption?

A

Transfer of drug from site of administration to blood stream.

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3
Q

What is the driving force for Passive Diffusion?

A

The concentration gradient across a membrane separating 2 body compartments.

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4
Q

Passive Diffusion means that the drug moves from _____ to ______.

A

A region of higher concentration to a region of lower concentration.

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5
Q

Give properties of Passive Diffusion:

A
  1. Does not involve a carrier.
  2. Is not saturable.
  3. Shows low structural specificity.
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6
Q

Which absorption mechanism allows access to a vast majority of drugs, to the body?

A

Passive Diffusion

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7
Q

Water soluble drugs penetrate the cell membrane through:

A

Aqueous Channel or Pores

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8
Q

Lipid-soluble drugs readily move across most biologic membranes due to:

A

Their solubility in the membrane lipid bilayers

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9
Q

Absorption through which, agents can enter the cell through specialized transmembrane carrier proteins that facilitate the passage of large molecules.

A

Facilitated Diffusion

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10
Q

Give Properties of Facilitated diffusion

A
  1. Carrier protein is involved which goes through conformational changes.
  2. It moves the drug from an area of higher to lower concentration.
  3. Can be saturated (via drugs that compete for the protein)
  4. Does not require energy.
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11
Q

Energy-dependent active transport in Active Transport, is driven by:

A

Hydrolysis of adenosine triphosphate

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12
Q

What is Active Transport?

A

A few drugs that closely resemble the structure of naturally occurring metabolites are actively transported across cell membranes using these specific carrier proteins.
Moved from an area of lower to higher concentration via Hydrolysis of ATP to ADP.

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13
Q

Is Active Transport Saturable?

A

Yes. Active transport systems are selective and may be competitively inhibited by other cotransported substances.

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14
Q

What is Endocytosis?

A

Transportation of an exceptionally large drug molecule through cell membrane.

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15
Q

How is drug molecule transported in endocytosis?

A

By engulfing of the large molecule via cell membrane and pinching of the drug filled vesicle.

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16
Q

What is the reverse process of endocytosis?

A

Exocytosis.

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17
Q

what is exocytosis used for?

A

For excretion of large molecules.

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18
Q

Give example of Endocytosis.

A

Vit B12 is transported across the gut wall via endocytosis

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19
Q

Give example of exocytosis.

A 
Certain neurotransmitters (for example, norepinephrine) are stored in intracellular membrane-bound vesicles
in the nerve terminal and are released by exocytosis
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20
Q

What are the factors influencing drug absorption?

A
  1. pH
  2. Blood flow to the absorption site
  3. Surface area
  4. Contact time with the absorption surface.
  5. Expression of p-glycoprotein.
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21
Q

A drug passes through the membrane more readily if it is:

A

Uncharged

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22
Q

_____ is the measure of strength of a compound with a proton.

A

pKa

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23
Q

Th lower the pKa, the more ____ the drug is, The higher the pKa, the more ______ the drug is.

A

Acidic ; Basic

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24
Q

For a weak acidic drug, which form can pass through the membrane. HA or A-

A

HA

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25
Q

For a weak basic drug which from can pass through the membrane. HB or B

A

B

26
Q

Highly lipid-soluble drugs rapidly cross membranes and often enter tissues at a rate determined by:

A

Blood flow

27
Q

Absorption is favored more from

a. Stomach
b. Intestine

A

b. Intestine

due to more blood flow and larger surface area

28
Q

The surface area of intestine is _____ times more than the stomach.

A

1000 times

29
Q

Severely reduces blood flow to cutaneous tissues, thereby minimizing the absorption from SC administration

A

Shock

30
Q

In diarrhea, the absorption of drug is not well because:

A

The drug moves too quickly through GI tract, giving less time of contact.

31
Q

The presence of ____ in the stomach both dilutes the drug and slows gastric emptying.

A

Food

32
Q

A drug taken with a meal is generally absorbed:

a. more rapidly
b. more slowly

A

b. more slowly

33
Q

Anything that delays the transport of the drug from the stomach to the intestine delays the:

A

Rate of absorption of the drug

34
Q

_________ is a multidrug transmembrane transporter protein responsible for transporting various molecules, including drugs, across cell membranes

A

P- glycoprotein

35
Q

Function of p-glycoprotein in Liver?

A

Transporting drug into bile for elimination.

36
Q

Function of p-glycoprotein in Kidney?

A

Pumping drug into urine for excretion.

37
Q

Function of p-glycoprotein in Placenta?

A

transporting drugs back into maternal blood,

thereby reducing fetal exposure to drugs

38
Q

Function of p-glycoprotein in Intestine?

A

Transporting drugs into the intestinal lumen and

reducing drug absorption into the blood

39
Q

Function of p-glycoprotein in brain?

A

Pumping drugs back into blood, limiting

drug access to the brain.

40
Q

In areas of high expression, P-glycoprotein _____drug
absorption.
a. Increases
b. Decreases

A

b. Decreases

41
Q

In addition to transporting many drugs out of cells, p-glycoprotein is also associated with _______

A

multidrug resistance

42
Q

Bioavailability is:

A

The fraction of administered drug that reaches the systemic circulation

43
Q

If 100 mg of a drug are administered

orally, and 70 mg of this drug are absorbed unchanged, the bioavailability is:

A

0.7 or 70%

44
Q

Determining bioavailability is important for

calculating drug dosages for _____ routes of administration.

A

non-intravenous

45
Q

Factors affecting bioavailability of a drug?

A
  1. Route of administration
  2. First pass hepatic metabolism
  3. Chemical Properties of the drug (chemical instability)
  4. Physical properties of the drug (solubility)
  5. Nature of drug formulation
46
Q

Bioavailability is determined by:

A

Comparing plasma levels of a drug after a particular route of administration vs plasma drug levels after IV administration.

47
Q

The ratio of the area calculated for oral administration compared with the area calculated for IV injection if doses are equivalent

A

Bioavailability

48
Q

Equation for bioavailability =

A

AUC Oral
————– x 100
AUC Injected

49
Q

After oral administration, The drug absorbed from GI tract, enters in portal circulation instead of Systemic circulation. This is called:

A

The first pass effect

50
Q

Give an example of a drug with low oral bioavailability due to first pass.

A

NITROGLYCERINE
(more than 90% is cleared during a single passage through Liver.
So it is instead administered Sublingually)

51
Q

Very hydrophilic drugs are poorly absorbed because:

A

Inability to cross the lipid-rich cell

membranes

52
Q

Extremely hydrophobic drugs are poorly absorbed because:

A

they are totally insoluble in aqueous body fluids, therefore cannot gain access to the cell surface

53
Q

For a drug to be readily absorbed, it must be:

A

Largely hydrophobic, yet have some solubility in aqueous solutions.
i.e weak acid or weak base

54
Q

_____ is unstable in the pH of the gastric contents.

A

Penicillin G

55
Q

______are destroyed in the GI tract by degradative enzymes

A

Insulin

56
Q

Two related drug preparations are__________ if they show comparable bioavailability and similar times to achieve peak blood concentrations.

A

Bioequivalent

57
Q

Two similar drug products are ________ if they are pharmaceutically equivalent with similar clinical and safety profiles

A

therapeutically equivalent

58
Q 
Clinical effectiveness often depends on
a. The maximum serum drug concentrations
b. The time required (after administration) to reach
peak concentration
c. Both
A

Both

59
Q

Two drugs that are bioequivalent may not be ________

A

therapeutically equivalent

60
Q

Excipients such as binders and dispersing

agents can influence the ease of ________

A

Dissolution

Pharmacokinetics (5 decks)

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