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Pharmacology > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

Pharmacodynamics

A

What a drug does to the body
Mechanism of action and effects on cellular functions

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2
Q

Pharmacokinetics

A

What the body does to a drug
ADME

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3
Q

What is ADME?

A

Absorption
Distribution
Metabolism
Excretion

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4
Q

What are well perfused organs and how does this impact drug action?

A

Lungs and kidneys
Takes up and releases drug quickly

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5
Q

What are poorly perfused tissues and how does this impact drug action?

A

Fat
Takes up and releases drug slowly

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6
Q

How does the size of a drug effect the diffusion coefficient?

A

The smaller the drug, the higher the diffusion coefficient

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7
Q

Why is vacular endothelium more complicated in terms of diffusion?

A

Its anatomical disposition and permeability varies from one tissue to another
Gaps between endothelial cells are packed with a loose matrix of proteins that act as filters so large molecules are retained

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8
Q

Lipid solubility

A

One of the most important factors in pharmacokinetic characteristics of a drug
Non polar molecules dissolve freely and can penetrate membranes freely

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9
Q

How does pH effect pharmacokinetic properties of a drug?

A

Affects steady state distribution of drugs between aqueous compartments

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10
Q

Basic environments

A

Favour dissociation of acids

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11
Q

Weak acids

A

Become trapped in basic compartments

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12
Q

Urinary acidification

A

Retards the excretion of weak acids

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13
Q

What effects does increasing plasma pH have on drugs?

A

Causes weakly acidic drugs to be extracted from the CNS into the plasma where they get trapped
Causes neurotoxicity

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14
Q

Bioavailability

A

Fraction of ingested dose that gains access to circulation
Low if drugs is metabolised in gut or liver or if there is vomiting

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15
Q

Intravenous administration

A

Most direct and reliable route and is fast acting
Used in emergencies

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16
Q

Subcutaneous or intramuscular injection

A

Next fastest route
Variable absorption depending on the site of injection and local blood flow

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17
Q

What is an intrathecal injection as a method of drug administration?

A

Lumbar puncture used to produce regional anaesthesia

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18
Q

Oral administration

A

Most common and easiest
Most drug absorption occurs in the gut by large SA and passive diffusion

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19
Q

What factors effect the rate of absorption when using oral administration?

A

Gut motility, presence of food, particle size and encasing of tablet and physiochemical factors

20
Q

What carriers are involved in carrier mediated transport?

A

Solute carrier transporters
ATP binding cassette transporters

21
Q

What substances take part in carrier mediated transport?

A

Sugars, amino acids, metal ions, neurotransmitters

22
Q

Where are solute carrier transporters present in the body?

A

Blood brain barrier, GI tract, renal tubule, biliary tract and placenta

23
Q

What are free form drugs?

A

Weak acids or bases that will exist at equilibrium between charged and uncharged form depending on the pH of the compartment

24
Q

What drugs do not readily enter interstitial and intracellular compartments?

A

High molecular weight drugs like insulin or heparin

25
Q

What is the volume of distribution of a drug?

A

the amount of drug that would be required to hold the amount of drug in the body as measured in the plasma

26
Q

Distribution of a drug at equilibrium between two compartments will depend on:

A

Permeability across tissue barriers
Binding within compartment
pH partition and fat:water partition

27
Q

Why is drug distribution to the CNS often limited by the BBB?

A

Endothelial cells lining blood vessels in the CNS form tight junctions impermeable to water molecules

28
Q

What can cross the blood brain barrier?

A

Lipid soluble drugs like ethanol and caffeine cross easily

29
Q

When can the tight junctions of the blood brain barrier become leaky?

A

During inflammation, like during meningitis

30
Q

How does binding to plasma proteins effect distribution?

A

High protein binding can lead to unexpected large increases in concentration of a drug as the binding sites become saturated

31
Q

What can act as a drug reservoir? When can this pose an issue?

A

Body fat
Acutely administered general anaesthetic drugs that are lipophillic

32
Q

What is albumin?

A

A plasma protein
Competition for it can cause unwanted side effects by displacing other drugs

33
Q

What is phase 1 of drug metabolism?

A

Catabolic reactions which can produce a more reactive compound

34
Q

What is phase 2 of drug metabolism?

A

Anabolic reactions which involve conjugation to produce an inactive product

35
Q

What are the two routes to the liver for drug metabolism?

A

The portal system
Through the plasma

36
Q

Products of which metabolism phase may have increased toxicity and carcinogenicity?

A

Phase 1

37
Q

What are the phase 1 reactions carried out by?

A

Cytochrome P450 family of enzymes

38
Q

First order kinetics

A

Rate of elimination is directly proportional to drug concentration

39
Q

What are the effects of drugs on plasma half life?

A

The same irrespective of drug concentration and can be easily calculated as it is only dependent on the rate of elimination

40
Q

What does steady state level mean?

A

Where rate of infusion is matched by the rate of elimination

41
Q

What is saturation kinetics?

A

Doesn’t show exponential time courses of disappearance but has a linear relationship
Drug is eliminated at a constant rate independent of concentration

42
Q

What type of kinetics is saturation kinetics associated with? What drugs act this way?

A

Zero order kinetics
Ethanol and Phenytoin

43
Q

Why does ethanol show saturation kinetics?

A

Alcohol dehydrogenase reaches a maximum at relatively low levels of ethanol due to low availability of its cofactor

44
Q

Hasselbach equation

A

HA -> H+ + A-
BH -> B + H+

45
Q

pKa =

A

pH + log10[HA] / [A-]
pH + log10[BH+] /[A-]

Pharmacology (5 decks)

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