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Pharmacology Flashcards

1
Q

Define pharmacodynamics?

A

What a drug does to the body (biological effects and mechanisms of action)

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2
Q

Define pharmacokinetics?

A

What the body does to a drug (absorption, distribution, metabolism and excretion of drugs and their metabolites)

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3
Q

What is the medical definition of a drug?

A

Any synthetic or natural substance used in the treatment, prevention or diagnosis of disease

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4
Q

What are receptors?

A

Macromolecules that mediate the biological actions of hormones and neurotransmitters

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5
Q

What are agonists?

A

Drug that binds to receptor to produce a response

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6
Q

What are antagonists?

A

Drug that blocks the action of agonists

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7
Q

What is the affinity of a drug?

A

Binding step

Strength of association between ligand and receptor

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8
Q

What is the efficacy of a drug?

A

Activation step

The ability of an agonist to evoke a cellular response

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9
Q

Do agonists possess affinity or efficacy?

A

Both

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10
Q

Do antagonists possess affinity or efficacy?

A

Affinity only

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11
Q

What is the speed of reaction of a drug with low affinity?

A

Slow

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12
Q

What is the speed of reaction of a drug with high affinity?

A

Fast

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13
Q

What is the level of response of a drug with low efficacy?

A

Low

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14
Q

What is the level of response of a drug with high efficacy?

A

High

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15
Q

What is the relationship between agonist concentration and receptor occupancy?

A

Hyperbolic relationship showing saturation

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16
Q

What is the EC50?

A

Concentration of agonist which produces a half maximal response

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17
Q

What is the relationship between agonist concentration and response?

A

Sigmoidal, semi-logarithmic plot

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18
Q

Why is the sigmoidal plot better than that of the hyperbolic plot?

A

Encompasses a greater range of values

Gives a more accurate reading of the EC50

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19
Q

What is the potency of a drug?

A

The concentration of a drug required to produce an effect

i.e. the more drug needed, the less potent it is

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20
Q

How would a partial agonist be distinguished on a sigmoidal plot?

A

It will have less than 100% maximal response

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21
Q

How does competitive antagonism occur?

A

Agonist and antagonist bind to the same site (orthosteric)

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22
Q

How does non-competitive antagonism occur?

A

Antagonist binds to a separate allosteric site
Causes a conformational change in receptor change - even if agonist binds, receptor remains inactive in presence of antagonist

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23
Q

What is the effect of adding a non-competitive antagonist on the agonist-response curve?

A

No shift
Maximal response depressed
Slope clearly flattened

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24
Q

What is the effect of adding a competitive antagonist on the agonist-response curve?

A

Parallel shift to the right

No depression of maximal response

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25
What are the four phases involved in drug disposition?
Absorption Distribution Metabolism Excretion
26
What is absorption?
The process by which a drug enters the body, where the GI tract is considered outside
27
What is distribution?
The process by which a drug leaves the circulation an d enters the tissues perfused by blood
28
What is metabolism?
The process by which tissue enzymes catalyse the chemical conversion of a drug to a more polar form that is more readily excreted
29
What is excretion?
The processes that remove the drug from the body
30
How does solubility affect drug absorption?
Drug must dissolve in order to be absorbed
31
How does chemical stability affect drug absorption?
Protein based drugs would be digested before absorption and so cannot be given orally
32
How does the lipid to water partition coefficient affect drug absorption?
Drug must be able to dissolve in both lipid and water (amphipathic) Drugs with higher lipid solubility will have a higher membrane concentration and so cross the membrane quicker
33
How does the degree of ionisation of a drug affect drug absorption?
Only unionised forms will diffuse readily across membrane
34
What is the Henderson-Hasselbalch equation?
Acid pKa - pH = log(HA/A-) Alkali pKa - pH = log(BH+/B) Calculates the proportions of ionised and unionised drugs
35
In what environment do acid drugs become less ionised?
In an acidic environment
36
In what environment do basic drugs become less ionised?
In a basic environment
37
What factors affect GI absorption?
``` GI motility pH of absorption site Blood flow to site Way in which the tablet has been manufactured Physiochemical interactions Presence of transporters in the membrane ```
38
What is the oral availability of a drug?
The fraction go the drug that reached the systemic circulation after oral ingestion
39
What is the systemic availability of a drug?
The fraction of the drug that reaches the systemic circulation after absorption
40
What are the enteral routes of drug administration (GI)?
Oral Sublingual Buccal Rectal
41
What are the parenteral routes of drug administration (non GI)?
``` Intravenous Intramuscular Subcutaneous Inhalation Topical ```
42
What is the therapeutic ratio?
Maximum Tolerated Dose / Minimum Effective Concentration The higher the ratio, the safer the drug
43
What is Kabs?
The absorption rate constant
44
What is Kel?
The elimination rate constant
45
How is the initial dose of an IV drug calculated?
Mass / Volume | C0 = D / Vd
46
By how many half lives will the majority of drugs have left the body?
Five
47
What drives the rate at which drugs leave the body?
Drug concentration
48
For drugs exhibiting first order kinetics, what is the effect of doubling the dose of a drug?
Adds one half life to its duration of therapeutic effect Doubles the steady state plasma concentration Does not alter the time for a drug to reach steady state
49
What is the clearance of a drug?
The volume of plasma cleared of drug in unit time
50
Why is clearance important?
Determines the maintenance dose rate
51
How is rate of elimination calculated?
Clearance x Plasma Concentration
52
What is the steady state of a drug, and how long does it generally take to reach?
Rate of drug administration = rate of drug elimination | Approximately 5 half lives
53
What is the volume of distribution of a drug?
The volume into which a drug appears to be distributed with a concentration equal to that of the plasma
54
What is the loading dose?
An initial higher dose of drug given at the start of treatment before stepping down to a lower maintenance dose
55
Why is a loading dose used?
To decrease the time to steady state for drugs with long half loves
56
What is the half life of a drug?
The time taken for the concentration of drug in the plasma to halve
57
What are first order kinetics?
Where the rate of elimination is directly proportional to drug concentration
58
What are zero order kinetics?
Where the rate of elimination is constant, rather than proportional to the concentration of the drug
59
What are the aims of drug metabolism?
Convert drugs to more polar metabolites which are not readily absorbed in the kidney, and so are excreted Convert drugs to metabolites that are usually less pharmacologically active
60
What is the main organ of drug metabolism?
Liver
61
What occurs during phase 1 of metabolism in the liver?
Oxidation, reduction, hydrolysis Makes drugs more polar Adds chemically active group permitting conjugation in phase II
62
What occurs during phase 2 of metabolism in the liver?
Conjugation | Adds an endogenous compound increasing polarity
63
What are the cytochrome P450 family of Monooxygenases and what is their role in metabolism?
Haem proteins located in the ER of the liver | Mediate oxidation reactions in phase I of metabolism
64
How does the Monooxygenase P450 cycle cause oxidation?
Drug enters as substrate Molecular oxygen enters cycle One atom of oxygen is added to drug to yield the hydroxyl product The other oxygen atom gives water
65
What is glucuronidation?
Common phase II reaction involving the transfer of gulcuronic acid to electron wish atoms of the substrate
66
What three basic processes are involved in renal excretion of drugs?
Glomerular filtration Active tubular secretion Passive reabsorption by diffusion across the tubular epithelium
67
How can a drug avoid glomerular filtration?
By binding to a large plasma protein
68
What are the two independent transporter systems which actively secret drugs into the lumen of the nephron?
Organic anion transporter = Acidic drugs | Organic cation transporter = Basic drugs
69
What is potentially the most effective mechanism for drug elimination by the kidney?
Tubular secretion
70
How can drugs which are highly protein bound be excreted?
Tubular secretion
71
What factors influence tubular reabsorption of a drug?
Lipid solubility Polarity Urinary flow rate Urinary pH

Principles (13 decks)

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