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HMS120: Pharmacology > Pharmacokinetics- Distribution > Flashcards

Pharmacokinetics- Distribution Flashcards

1
Q

Define Distribution

A
  • process where the absorbed chemical moves away from the site of absorption to other areas of the body
  • process by which a drug is transferred from the blood stream (plasma) to tissues (interstitial fluid and cells)
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2
Q

What do the rate and degree of drug distribution depend on?

Hint: CAMP B

A

C: capillary permeability
A: accumulation in and redistribution to other sites
M: miscellaneous factors (i.e. age, obesity, diet, etc.)
P: protein binding (i.e. to albumin)

B: blood flow

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3
Q

What is Re-distribution?

A
  • when well-perfused organs initially receive most of the drug before being received by lesser perfused organs
  • results in the termination of drug action
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4
Q

What are the well-perfused organs?

Hint: BLacK

A

B: brain
L: liver
K: kidney

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5
Q

What are the lesser-perfused organs?

Hint: MS VF

A

M: muscle
S: skin

V: (most) viscera
F: fat

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6
Q

Where would the drug likely be found if there are very large drug molecules?

A

drug confined to circulation

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7
Q

Where would the drug be if drug molecules are very polar?

A

drug excluded by cell membrane

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8
Q

Where would the drug be if drug is lipophilic?

A

in fat within the cells

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9
Q

Why is drug distribution not uniform throughout the body?

A

because different tissues receive the drug from the plasma at different rates and to different extents

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10
Q

Define Volume of Distribution (Vd)

A
  • apparent volume of distribution
  • theoretical volume that would be necessary to contain the total administered drug at the same concentration as seen in the plasma
  • predicts whether drug will reside in blood or tissue
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11
Q

Where will water soluble drugs reside?

A

the blood

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12
Q

Where will lipid soluble drugs reside?

Hint: CAFe

A

C: cell membrane
A: adipose tissues
F: fat-rich areas

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13
Q

What is the Vd for drugs that are charged?

A

tend to bind to serum proteins -> increase in molecular size -> does not pass through cell membrane easily -> confined to circulation

  • low Vd
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14
Q

What is the Vd of hydrophilic or charged drugs?

A
  • low Vd
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15
Q

What is the Vd if there is an underlying disease of renal failure?

A
  • increased Vd

- due to fluid retention

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16
Q

What is the Vd if there is an underlying disease of liver failure?

A
  • increased Vd

- due to altered body fluid and plasma protein binding

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17
Q

What are factors that affect Vd?

Hint: MALT PWP

A

M: molecular weight of drug
A: acidity
L: lipid solubility
T: tissue perfusion

P: pathological condition
W: water solubility
P: plasma protein binding

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18
Q

Explain how the molecular weight of a drug affects Vd

A
  • low molecular weight of drugs -> high Vd (can pass through pores)
  • high molecular weight -> low Vd
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19
Q

Explain how the acidity of a drug affects Vd

A
  • acidic drugs have low Vd (high affinity for albumin)

- basic drugs have high Vd (high affinity for alpha-1 acid glycoprotein / free drug)

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20
Q

Examples of acidic drugs

Hint: Basic drugs don’t Bind To Plasma Very Fast

A 
Basic: bilirubin
Bind: bile acids
To: tetracycline
Plasma: penicillin
Very: Vitamin C
Fast: fatty acids
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21
Q

What do acidic drugs have high affinity for (blood binding)?

A

plasma albumin

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22
Q

What do basic drugs have high affinity for (blood binding)?

A

alpha-1 acid glycoproteins

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23
Q

Explain how lipid solubility of a drug affects Vd

A

lipid soluble drugs have high Vd

- can move through the plasma membrane freely

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24
Q

Explain how tissue perfusion of a drug affects Vd

A
  • low tissue perfusion means low Vd

- high tissue perfusion means high Vd

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25
Q

Explain how pathological conditions may affect Vd

A

e.g. in edematous conditions, water soluble drugs have high Vd

26
Q

Explain how water solubility of a drug affects Vd

A
  • water soluble drugs have low Vd

- due to the inability to cross the plasma membrane on its own

27
Q

Explain how plasma protein binding (PPB) of a drug affects Vd

A
  • high PPB of a drug means low Vd (increases the molecular size -> cannot pass through pores)
  • low PPB of a drug means high Vd
28
Q

What is the affect of lipid solubility of a drug on redistribution?

A
  • the greater the lipid solubility of the drug, the faster its redistribution
29
Q

Define Bioavailability

A

fraction of the administered drug that reaches the systemic circulation

30
Q

Define Absolute Bioavailability

A

compares the bioavailability of the active drug in systemic circulation following non-IV administration vs the same drug with IV administration

31
Q

When will the bioavailability of a drug be 100%?

A

when the drug is administered intravenously

32
Q

What is the purpose of absolute bioavailability?

A

to determine the best route of administration

33
Q

Define Relative Bioavailability

A

compares the bioavailability of formulation A of a certain drug compared with another formulation B (of the same drug)

34
Q

What is the difference between Absolute Bioavailability and Relative Bioavailability?

A
  • absolute bioavailability: compares bio-availabilities of (the same) active drug administered via non-IV vs IV
  • relative bioavailability: compares bio-availabilities of formulations of the same drug
35
Q

Define Bioequivalence

A

when two related drugs show comparable

  • bioavailability
  • similar times to achieve peak blood concentrations
36
Q

Define Therapeutic Bioequivalence

A

when two similar drugs show comparable

  • efficacy
  • safety
37
Q

What are factors that influence bioavailability?

Hint: FSCN (like fasten)

A

F: first-pass hepatic effect
S: solubility
C: chemical instability
N: nature of the drug formulation

38
Q

How does the first-pass effect influence bioavailability?

A
  • drug absorbed from the GI tract is first delivered to the liver before entering the systemic circulation
  • liver is where metabolism occurs -> if the drug is rapidly metabolised, the amount of unchanged drug that enters the system circulation is decreased
  • > greater the first-pass effect = less drug to reach systemic circulation
39
Q

Under what circumstances does hepatic first-pass effect take place?

A

when drug is administered orally

40
Q

When does the drug bypass first-pass effect?

A

when administered via:

  • IV
  • IM rectal
  • sublingual
41
Q

How does the solubility of the drug influence bioavailability?

A
  • hydrophobic drugs (increase bioavailability)

- hydrophilic drugs (decrease bioavailability)

42
Q

How does chemical instability influence bioavailability?

A

instability decreases bioavailability

i. e.
- penicillin G is unstable in pH of gastric contents
- insulin is destroyed in the GI tract by degradative enzymes

43
Q

How does the nature of the drug formulation influence bioavailability?

Hint: PEE

A

nature of drug formulation includes-
P: particle size
E: enteric coatings
E: excipients

  • can influence ease of dissolution -> therefore altering the rate of absorption
44
Q

How are drugs transported in the blood?

A
  • free form

- bound form

45
Q

What is the free form of a drug?

Hint: DAA

A
  • diffusible
  • active
  • available for metabolism and excretion
46
Q

What is the bound form of a drug?

A
  • bound to plasma albumin
  • inactive
  • neither metabolised nor excreted
47
Q

What can protein binding be divided into?

A
  • intracellular binding

- extracellular binding

48
Q

What is the significance of plasma-protein binding?

A
  • affects distribution (cannot pass through capillaries and cell membranes due to large molecular size)
  • inactive
  • non-diffusible
  • not available for metabolism nor excretion
  • reservoir (supplies free drug when required- stays within circulation longer)
49
Q

True or False:

The plasma-protein binding of drugs can be irreversible.

A

True

- binding of drugs to proteins is generally reversible & irreversible

50
Q

What constitutes for an irreversible plasma-protein binding of a drug?

A
  • when there is a covalent binding (rare)
51
Q

What constitutes for a reversible plasma-protein binding of a drug?

A

weak chemical bonds

  • hydrogen bonds
  • hydrophobic bonds
  • ionic bonds
  • Van der waal’s forces
52
Q

What happens when a irreversible plasma-protein binding occurs with a drug?

A
  • carcinogenicity or tissue toxicity
53
Q

What drug can bind to both primary and secondary site of albumin?

A

flucoxacillin

54
Q

What drug has three different binding sites on albumin?

A

indomethacin

55
Q

Example of basic drugs

Hint: LIP

A

L: lidocaine
I: imipramine
P: propranolol

56
Q

How do drugs bind to lipoproteins?

A

via hydrophobic bonds

57
Q

What does alpha-1 globulin bind to?

A

steroidal drugs

58
Q

What does alpha-2 globulin bind to?

A

Vitamins K, A, D, E

59
Q

What does Beta-1 globulin bind to?

A

ferrous ions

60
Q

What does Beta-2 globulin bind to?

A

carotinoids

61
Q

What does gamma-globulin bind to?

A

antigens

62
Q

How are some drugs displaced by other drugs?

A

drugs with high affinity for plasma proteins can displace other drugs/endogenous compounds that have lower affinity

HMS120: Pharmacology (13 decks)

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