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Drugs Flashcards

1
Q

What is pharmacokinetics?

A

Factors affecting drug movement in body

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2
Q

What factors affect pharmacokinetics?

A

Metabolism
Absorption
Distribution
Elimination

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3
Q

How can drugs be administered to the body?

A 
Orally
Intravenous
Subcutaneous
Intramuscular
Nasal
Transdermal (patches)
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4
Q

Regarding the drug distribution diagram, what is Cmax, Tmax and AUC?

A 
Cmax = peak concentration of drug in body
Tmax = time to reach Cmax
AUC = the area under the curve (on the diagram)
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5
Q

What is the therapeutic range of a drug?

A

The range of concentrations at which the drug is active in the body

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6
Q

What are the effects if a drug goes above or below its therapeutic range?

A 
Above = toxicity
Below = no effect on body
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7
Q

What is the bio availability of a drug?

A

The part of the drug which is carrying out its function

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8
Q

What is the bio availability of IV administration?

A

100%

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9
Q

What factors affect bio availability of orally administered drugs?

A

Formulation of drug
Ability to pass through barriers
Effects of drug on GI tract (digestion)
First pass metabolism

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10
Q

What is first pass metabolism?

A

The metabolism of the drug before it reaches site of absorption

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11
Q

What factors impact diffusion of drugs across the membrane of cells?

A

Ionisation - drugs may dissociate to form weak acids/alkalis in body (the degree of dissociation is dependent on pH) - the greater the ionisation, the more difficult it is for the drug to cross the membrane and vice versa
Lipid solubility - the more lipid soluble a drug is, the easier it can pass through the lipid membrane
Structure - drugs which mimic the structure and shape of naturally occuring substances will pass through membrane easier

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12
Q

What type of diffusion is more common for drugs - passive or active?

A

Passive

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13
Q

What factors affect drug absorption in the GI tract?

A

Gut motility - speed of gastric activity can affect how drugs are absorbed in the GI tract
Food/drink - certain foods may impair/enhance absorption
Illness - malabsorption (coeliac’s disease) may increase/decrease absorption of certain drugs and migraines reduces rate of stomach emptying and analgesic (painkiller) drugs

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14
Q

Medical relevance of first pass metabolism

A

We want to avoid this as we want as much of the drug to be absorbed at target site as possible
Some drugs can be administered in a method which avoids first pass metabolism but some drugs can only be administered in certain ways

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15
Q

Where does first pass metabolism occur?

A 
Gut lumen (acid, enzymes)
Gut wall (metabolic enzymes)
Liver (hepatic extraction ratio)
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16
Q

What are the benefits of intravenous medication?

A

Avoids first pass metabolism

100% bio availability

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17
Q

What are the benefits of sublingual medicine?

A

Avoids first pass metabolism

Enters circulation directly

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18
Q

What is the benefit of rectally administered medicine?

A

Avoids first pass metabolism

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19
Q

What are the benefits of topical medication?

A

Effects can be local or systemic
Avoids first pass metabolism
Can control dosage of drug given

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20
Q

What are the benefits of inhalation medication?

A 
Rapid effect 
Can have little systemic effects 
Little adverse effect
Drug is delivered to site of infection 
Small dose is used
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21
Q

What is the benefit of transdermal medication?

A

Provides controlled release

Avoids first pass metabolism

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22
Q

What factors impact drug distribution?

A

Plasma protein binding
Tissue perfusion (how the drug enters tissues)
Other drugs in body
Diseases
Membrane characteristics (blood-brain barrier or the blood-testes/ovaries barrier - the drug will have to be lipid soluble or active transport has to occur)
Elimination of drug

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23
Q

What is Vd (apparent volume of distribution)?

A

This is the volume of plasma which would be needed to account for the total concentration of the drug in the body (taken that the concentration of the blood in the plasma is the same as everywhere else in the body)

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24
Q

What is Cl (clearence)?

A

The concentration of the drug removed from the body after a certain length of time (measure in ml/min)

25
What is t1/2 (half-life)?
The time taken for the concentration of the drug in the body to half
26
What is excretion?
Removal of the drug from the body | Determines how long the drug can act for
27
What determines excretion of a drug?
``` Drug metabolism (liver) Drug exceretion (kidney) ```
28
Where does drug excretion mainly occur?
Kidney
29
What are the three mechanisms of renal excretion of drugs?
Glomerular filtration Passive tubular filtration Active tubular filtration
30
Describe glomerular filtration of the kidneys
Any unbound drug will be filtered at the glomerulus as long as its size/charge does not affect it Factors which affect glomerular filtration impact clearance rate of drugs
31
Describe passive tubular filtration
As the filtrate passes along renal tubules, it becomes more concentrated - as is the drug it is filtering Some of the drug may be reabsorbed into the body - only unionised parts of the drug This filtration is impacted by renal failure
32
Describe active tubular filtration
Drugs are actively secreted to proximal tubules | This is main method of excreting cationic and anionic drugs
33
Where abouts in the body does drug metabolism occur?
Liver Gut (lining) Lungs Kidney
34
What is drug metabolism?
Increase water solubility to aid in excretion of drug Most cases drug will either lose pharmacological activity, activate some metabolites or activate many metabolites (product of metabolism)
35
What happens when toxic metabolites are produced?
Direct toxicity Carcinogenesis Teratogenesis
36
What is the purpose of Phase 1 Metabolism?
Increase polarity of molecule and provide active sites | Prepare molecule for phase 2 metabolism
37
What enzymes are key for phase 1 metabolism?
Cytochrome P-450
38
What are some important isoforms of cytochrome P-450?
CYP3A4 CYP2D6 CYP1A2
39
What is the function of CYP3A4?
Found in the liver | Metabolises methadone, simvastatin and diazepam
40
What is the function of CYP2D6?
``` Metabolises antidepressants Metabolises antipsychotics Converts morphine to codiene Not expressed in 5-10% of population Induction by smoking ```
41
What is the function of CYP1A2?
Induced by smoking | Metabolism of theophyline
42
What is the function of Phase 2 metabolism?
Involves conjugation | Increase water solubility to aid in excretion
43
What are the effects of conjugation?
Usually inactivates compounds (some may remain active) | Involves attachment of glucuronic acid, gluthianone, sulphate or acetate to metabolite of phase 1
44
What factors effect drug metabolism?
``` Other drugs/substances Race - different races may have different forms of P-450 genes Age Hepatic blood flow Liver disease Genetics ```
45
How can other drugs/substances effect drug metabolism?
Enzyme induction - drug metabolising enzyme is induced by other substances which leads to decreased drug effect (alcohol/smoking/phenytoin/carbamazapine do this) Enzyme inhibiton - certain drugs inhibit drub metabolising enzymes (some irreversible reactions). Examples include clarithromycin, erythromycin and cimetidine
46
How can genetics effect drug metabolism?
Many forms of genes for drug metabolising enzymes therefore difference in gene expression between induviduals can lead to absence or presence of drug metabolising enzymes Certain mutations can lead to absence of drug metabolising enzymes - toxicity Certain mutations may lead to enhanced expression of drug metabolising enzymes - no effect of drug
47
How can age have an effect on drug metabolism?
Absence of drug metabolising enzymes in foetuses/premature babies Poor kidney function in young May lead to build up/toxicity of drug in young By age 2 - faster metabolism of drug than in adults (some drugs) Peak metabolism of drug during adolesence
48
Explain importance of pharmacogenetics
Different forms of genes for drug metabolising enzymes can lead to different gene expression between people Lack of drug metabolising enzymes will lead to toxicity Enhanced expression will mean drug has no effect on body
49
What are the advantages and disadvantages of solutions (orally administered medication?
Advantages: Useful for elderly/children/those with problems swallowing Absorbed quickly (mostly by small intestine) Disadvantages: Absorption depends on gastric emptying
50
What are the advantages and disadvantages of suspensions (orally administered medication)?
Advantages: Good for insoluble drugs as better tolerance Disadvantages: Only small volume can be used
51
What are the advantages and disadvantages of tablets & capsules (orally administered)?
Advantages: Mass produced Convenient Stable Disadvantages: First pass metabolism Absorption depends on rate of tablet break down
52
What are the advantages of enteric coated tabelts (orally administered)?
Delays breakdown of tablet till small intestine Coating protects tablet from stomach acid (omeprazole) Coating protects stomach from drug (aspirin)
53
What are the advantages of prolonged release tablets (orally administered)?
``` Advantages: Maintains drug in therapeutic range Better compliance rate Ideal for chronic conditions Reduces need for frequent dosing ```
54
What are the advantages of buccal/sublingual medicines?
Bypass first pass metabolism | Small and dissolvable tablets
55
What are advantages of rectally administered medication?
Ideal for young, elderly or those with difficulty swallowing
56
Where is intramuscular injections injected and what is a disadvantage of this?
Injected into muscle mass | Can be painful
57
What is an advantage of subcuteanous injection?
Easy to use
58
What are some advantages of transdermal medication?
Bypass first hepatic inactivtion | Controlled release/dosage of drug
59
What are some advantages and disadvantages of inhaled medication?
``` Advantages: Rapid effect Effect is direct to site Little systemic effect Small dosage used Reduced adverse effects ``` Disadvantages: Patient education is required

Principles of Disease (2 decks)

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