27 - Introduction to Pharmacokinetics Flashcards

1
Q
Steps of pharmacokinetics
1)
2)
3)
4)
a) 
b)
A

1) Administration
2) Absorption
3) Distribution
4) Elimination
a) Metabolism
b) Excretion

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2
Q
Factors influencing choice of administration route 
1)
2)
3)
4)
A

1) Patient preference
2) Cost
3) Bioavailability
4) Local system effect

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3
Q

Local vs systemic administration

A

Local - Drug exerts effect at or near site of introduction. Access to tissues limited by absorption

Systemic - Drug enters bloodstream. Accesses many tissues based on distribution.

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4
Q

When is a drug administered locally?

A

1) If it is a poorly-absorbed drug

2) To limit off-target effects in other tissues

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5
Q

Systemic routes that require drug to be absorbed

A

Oral, skin, lungs, nose, rectum, injectable

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6
Q

Systemic route of administration that doesn’t require absorption of drug

A

Intravenous

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7
Q

Manner in which most drugs are eliminated from the bldy

A

At a rate proportional to the concentration in plasma

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8
Q

Name for when drugs have distributed in body as if body were a single compartment

A

Drug equilibrium

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9
Q

Aspects of drug distribution
1)
2)
3)

A

1) Rarely uniform
2) Driven by circulation
3) Generally rapid (when reaches distribution equilibrium)

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10
Q

Factors affecting drug distribution
1)
2)
3)

A

1) Molecular size
2) Ability to bind plasma proteins
3) Lipid solubility

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11
Q

Effect of drug binding plasma proteins

A

Plasma proteins are much harder for kidneys to excrete, harder to transport across vascular endothelium

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12
Q

Effect of high lipid solubility of a drug

A

Leads to sequestration in lipid

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13
Q

Only type of drug able to cross blood brain barrier

A

Lipid soluble

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14
Q

Drug reservoirs in the body effects
1)
2)
3)

A

1) Can prolong action of drug (if released from store as concentration falls)
2) Can quickly terminate action (if stored drug has high capacity)
3) Can lead to slow distribution (if store has high capacity)

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15
Q

Places where drugs can find a reservoir
1)
2)
3)

A

1) Plasma proteins (only get into tissues if displaced from protein)
2) Cells (accumulation due to active transport or specific binding)
3) Lipids (blood supply is poor and capacity large, so may lead to slow distribution)

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16
Q

Volume of distribution

A

Volume of water that the total amount of drug administered would occupy if it had the same concentration as that in the plasma.

17
Q

Equation for volume of distribution (Vd)

A

Vd = Amount of drug in body/Drug concentration in plasma

18
Q

Effect on Vd if drug binds plasma protein

A

Lowers Vd, as more drug is retained in plasma

19
Q

Effect on Vd if drug binds tissues, is taken up by cells

A

Increases Vd, as less drug is in plasma

20
Q

What does Vd tell us clinically?

A

How much drug to give to get a particular amount of drug in plasma

21
Q

Excretion

A

Drug elimination by kidney

22
Q

Metabolism

A

Drug elimination by liver

23
Q

Places from which excretion can occur
1)
2)
3)

A

1) Bowman’s capsule/glomerular capillary - Glomerular filtration
2) Tubule - Tubular secretion
3) Tubule - Tubular reabsorption

24
Q

Is tubular secretion an active or passive process?

A

Active

25
Q

Is tubular reabsorption an active or passive process?

A

Passive

26
Q

Glomerular filtration rate

A

~120mL/minute.
Takes drugs out of blood through leaky glomerulus.
Can’t take plasma-protein-bound drugs

27
Q

Tubular secretion

A

Takes drugs out of blood.
Active process.
Can take plasma-protein-bound drugs out of the blood.
Can be competitively inhibited

28
Q

Tubular reabsoption

A

Takes drugs back into blood
Passive movement across cell membranes of of tubule and peritubular capillary
pH-dependent

29
Q

How is lipid solubility affected by pH?

A

Acidic drugs are uncharged at low pH (A-H), charged at higher pH (A- + H+).

Basic drugs are charged at low pH (BH+), uncharged at higher pH (B + H+)

30
Q

Example of how tubular reabsorption can be manipulated therapeutically

A

Aspirin overdose.
Administer NaHCO3, make urine basic.
Increases amount of ionised aspirin, which reduces reabsorption, increases excretion

31
Q

Renal clearance

A

Amount of drug removed by kidneys/time

32
Q

Maximum renal clearance rate

A

800mL/minute

33
Q

Clearance

A

Total amount of drug cleared from body/time.

Clearance(kidney)+clearance(liver)+clearance(other)

34
Q

Drug metabolism

A

Biotransformation in most tissues, but mainly in liver.

Enzyme-catalysed reactions to increase water-solubility of drug to facilitate excretion

35
Q

Phase I metabolism

A

Create a new functional group on drug (EG: -OH, -NH2, -COOH)

36
Q

Enzyme superfamily responsible for many phase I drug metabolism actions

A

Cytochrome p450

37
Q

Phase II metabolism

A

Conjugation of a water-soluble molecule to drug (EG: glucuronyl transferase conjugating UDP-glucuronic acid to drug)

38
Q

Effect of phase II metabolism

A

Methyl, acetyl, sulphate, glutathione often attached
Products almost always inactive
More water-soluble products

39
Q

Equation to calculate drug clearance

A

(Drug concentration in - drug concentration out)/drug concentration initial * blood flow