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Pharmacology 2 Flashcards

1
Q

What is Pharmacodynamics?

A

How the drug affects the body

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2
Q

What is pharmacokinetics?

A

How body affects the drug
ADME Absorption, Distribution, Metabolism, Excretion

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3
Q

Drug Receptor types

A

Ligand-gated ion channels - nicotinic ACh receptors

G Protein Coupled receptors (GPCR’s) - beta-adrenoceptors

Kinase-linked receptors - for growth factors

Cytosolic/nuclear receptors - steroid

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4
Q

What questions should you ask when prescribing a drug, with pharmacokinetics in mind?

A

How quickly will drug reach its site of action? How quickly will I see a response?
Drug interactions likely?
Is a dose adjustment needed in certain disease states?
What monitoring is required?

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5
Q

What mechanisms do drugs use to permeate membranes?

A
  1. Passive diffusion through hydrophobic membranes - lipid soluble molecules
  2. Passive diffusion through aqueous pores - only v small soluble drugs, e.g. lithium
  3. Carrier mediated drugs - quite unusual, basically when proteins that usually transport sugars, amino acids etc transport drugs
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6
Q

How does drug ionisation affect drug absorption?

A

Ionised drugs have poor lipid solubility
∴ only unionised drugs can pass

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7
Q

Why are the majority of medications PO?

A

Convenient
Cost-effective

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8
Q

Where are medications that are weak bases best absorbed? Why?

A

In the small intestine
bc small intestine has a pH of ~ 6.5 ∴ more likely to be similar pH to pKa of medication (the pH at which ionised & unionised drug is 50/50)

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9
Q

Where are medications that are weak acids best absorbed? Why?

A

In stomach
bc stomach has a pH of ~ 3 ∴ more likely to be similar pH to pKa of medication (the pH at which ionised & unionised drug is 50/50)

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10
Q

What factors affect the oral drug absorption in the stomach?

A

Gastric enzymes - digest the drug, esp large protein drugs e.g. insulin (∴ never given orally)

Low pH - can degrade

Full stomach = slower absorption

Gastric motility - can be altered by drugs/disease

Prev. surgery

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11
Q

What factors affect the oral drug absorption in the small intestine?

A

Drug structure - large/hydrophillic molecules are poorly absorbed

Medicine formulation - i.e. capsule has a coating to control release
Modified release slows rate of absorption (bc less freq dosing)

P-glycoprotein - will remove substrates from endothelial cells back into lumen lol

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12
Q

What is first pass metabolism?

A

Metabolism of drugs which prevents them from reaching systemic circulation
(The fraction of drug lost at absorption)

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13
Q

How does first pass metabolism occur?

A

Degradation by enzymes in intestinal wall
&
Absorption from intestine into hepatic portal vein and metabolism via liver enzymes

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14
Q

What is bioavailability?

A

Proportion of administered dose which reaches the systemic circulation

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15
Q

What is bioavailability (F) dependent on?

A

Dependent on extent of drug absorption and extent of first pass metabolism
NOT dependent on rate of absorption

Varies w/ route of administration and between individuals
e.g. tablet has lower bioavailability (F) than IV

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16
Q

What is bioavailability expressed as?

A

% or fraction

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17
Q

Pros of PR route

A

Local administration
Avoids first pass metabolism
Helps if patients has severe N/V ∴ can’t take meds orally

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18
Q

Cons of PR route

A

Absorption is variable
Patient preference

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19
Q

Example of PR medication

A

Diazepam suppositories for epileptic seizures

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20
Q

Pros of INH route

A

Well perfused large SA
Local administration

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21
Q

Cons of INH route

A

Inhaler technique might be ineffective

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22
Q

Example of INH route meds

A

Gaseous anaesthetic
Salbutamol inhaler

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23
Q

Pros of SC route

A

Faster onset than PO
Formulation can be changed to control absorption rate

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24
Q

Cons of SC route

A

Not as rapid as IV

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25
Examples of SC route meds
Long acting insulin for T1DM and T2DM
26
Pros of TD route
Provides continuous drug release Avoids first pass metabolism
27
Cons of TD route
Only suitable for lipid soluble drugs Slow onset of action
28
Examples of TD route medication
Fentanyl patches for severe chronic pain
29
What factors influence distribution?
1. Molecule size (small, ↑ distribution) 2. Lipid solubility (if lipophillic, ↑ distribution) 3. Protein binding (if NOT protein bound, ↑ distribution)
30
What is the volume of distribution (Vd)?
Also sometimes known as apparent volume of distribution Theoretical vol a drug will be distributed in the body Vol of plasma required to contain the total administered dose If well distributed, high Vd If poorly distributed, low Vd
31
What is the blood brain barrier?
Membrane that separates foreign substances in blood from CNS
32
Describe the physical aspect of the BBB
Continuous layer of endothelial cells with tight junctions Has high number of efflux pumps that remove water soluble molecules
33
How can drugs reach the CNS?
High lipid solubility - can permeate and diffuse across BBB Intrathecal route Inflammation - causes BBB to be leaky ∴ drugs can cross
34
In actuality, what must you think about when prescribing drugs, in relation to distribution?
Careful w dosing drugs with a small Vd - using actual body weight in obese patients e.g. Aciclovir NOT distributed to fat ∴ should be dosed based on ideal body weight, not actual Distribution changes in diff disease states (i.e. sepsis = leaky blood vessels = BBB penetration) Age changes body composition, which changes Vd of water soluble drugs Drugs that can cross BBB have CNS s/e
35
What is drug elimination?
The process by which the drug becomes no longer available to exert its effect on the body
36
Name 2 methods of drug elimination
Metabolism - modification of drug to new chemical entity Excretion of unchanged drug
37
What are the 2 phases of metabolism?
1. Oxidation / Reduction / Hydrolysis to introduce reactive group to chemical structure 2. Conjugation of functional group to produce hydrophillic, inert molecule then excreted
38
What cytochrome is mainly responsible for Phase 1 metabolism? Where are these located?
Cytochrome P450 (CYP450) Mostly in liver (also small intestine, lung)
39
When will CYP enzyme function vary?
Genetic variation ↓ Function in severe liver disease Interactions w/ drugs/foods which can ↑ or ↓ activity
40
How many CYP450 enzymes are there?
57
41
What CYP enzyme has the substrates caffeine, paracetamol, theophylline and warfarin?
CYP 1A2
42
What CYP enzyme has the substrates ibuprofen and warfarin?
CYP 2C9
43
What CYP enzyme has the substrates codeine and warfarin?
CYP 2D6
44
What CYP enzyme has the substrates simvastatin, warfarin, DOACs, carbamazapine and diltiazem?
CYP 3A4
45
What substrates are associated with CYP**1A2**?
Caffeine, paracetamol, theophylline, warfarin
46
What substrates are associated with CYP**2C9**?
Ibuprofen, warfarin
47
What substrates are associated with CYP**2C19**?
Omeprazole, phenytoin
48
What substrates are associated with CYP**2D6**?
Codeine, warfarin
49
What substrates are associated with CYP**3A4**?
simvastatin, warfarin, DOACs, carbamazapine and diltiazem
50
Which are the most signif CYP for drug metabolism?
3A4, 2C9, 2C19, 1A2, 2D6
51
In actuality, what must you think about when prescribing drugs, in relation to metabolism?
If severe liver impairment, is metabolism reduced? ∴ reduced dose? additional monitoring? avoid?? Drug interactions Saturation of metabolic pathways can lead to accumulation or toxicity (paracetamol overdose)
52
If normal dose of paracetamol, how is it metabolised?
Via glucuronidation and sulphation to form a non-toxic metabolite
53
If paracetamol overdose, how is it metabolised? What is the result? How do we treat this?
Normal pathway is saturated ∴ Oxidation by CYP2E1 Forms NAPQI (v toxic) Causes hepatocyte necrosis ∴ liver failure We would give **IV n-acetyl cysteine** (NAC) Replenishes body's stores of glutathione ∴ glutathione conjugation ∴ produces a non-toxic metabolite :)
54
When would we give a reduced paracetamol dose?
In low body weight patients Or if severe hepatic impairment
55
In what forms can drugs/metabolites be excreted?
Liquids - small polar molecules e.g. **urine**, bile, sweat, tears, breast milk Solids - large molecules e.g. faeces (thru biliary excretion) Gases - volatiles e.g. expired air
56
What is the first process that accounts for renal excretion?
1. **Glomerular filtration** Free/unbound drug molecules will pass through V large molecules will be excluded and will go thru efferent arteriole
57
What is the 2nd process of renal excretion?
2. **Active tubular secretion** Drug molecules transported from blood into renal tubule thru carriers (organic anion transporter (OAT) & organic cation transporter (OCT)) Can clear protein bound drugs Most effective renal clearance mechanism
58
What is the 3rd process of renal excretion?
3. **Passive reabsorption** Diffusion down conc gradient from tubule into peritubular capillaries Hydrophobic drugs diffuse easily Highly polar drugs will be excreted
59
Types of Adverse drug reactions
ABCDEFG **A**ugmented **B**izarre **C**hronic/continuing **D**elayed **E**nd of use/withdrawal **F**ailure of treatment **G**enetic
60
What is Augmented ADR caused by?
Exaggerated effect of drugs pharmacology at therapeutic dose Usually not fatal
61
What is the most common ADR?
Augmented (80%)
62
When is Augumented ADR dependent on?
Dose dependent Reversible when drug is withdrawn
63
Give some examples of Augmented ADR
AKI w/ ACE-i Bradycardia w/ beta blockers Hypoglycaemia w/ gliclazide, insulin Resp depression w/ opiates Bleedings w/ anticoag
64
Describe Bizarre ADRs
Not related to pharm Not dose related Can cause serious illness/death Symptoms don't always resolve when stopping drug
65
Give examples of a Bizarre ADR
Anaphylaxis w/ penicillin Tendon rupture w/ quinolone abx Steven Johnson Syndrome w/ IV vancomycin
66
What is a Chronic/Continuous ADR?
An ADR that continues after drug has been stopped
67
Give examples of Chronic/Continuing ADR
Osteonecrosis of the jaw w/ bisphosphonates HF w/ pioglitazone
68
What is a delayed ADR?
ADRs that become apparent some time after stopping drug
69
Give an example of a delayed ADR
Leucopenia w/ chemo
70
What is an End of Use/Withdrawal ADR?
ADR that develops after drug has been stopped
71
Give examples of End of Use/Withdrawal ADR
Insomnia after stopping benzodiazepine Rebound tachycardia after stopping BB
72
What could cause a Failure of treatment ADR?
Drug-drug or drug-food interaction Poor compliance with administration instructions
73
Give examples of a Type F ADR
Failure of bisphosphonates due to taking w/ food Failure of DOAC due to enzyme inducer (e.g. carbamazepine)
74
What is a Genetic ADR?
When drug causes irreversible damage to genome
75
Give an example of a Genetic ADR
Phocomelia in children of women taking thalidomide
76
Other than the ABCDEFG classification, what is another way of classifying ADRs?
DoTS **Do**se-relatedness **T**iming **S**usceptibility
77
Describe the Do in DoTS
**Do**se relatedness Looks at the dose you might get a ADR // _Hypersusceptibility reaction_ When you get an ADR at a subtherapeutic dose e.g. anaphylaxis w/ penicillin _Collateral effect_ ADR at a therapeutic dose e.g. hypokalaemia w/ loop diuretic _Toxic effects_ ADR at subpratherapeutic dose e.g. liver damage w/ paracetamol
78
Describe the T in DoTS
**T**iming When does ADR develop in relation to the drug taken TYPES : Rapid First dose Early Intermediate Late Delayed
79
Describe the S in DoTS
**S**usceptibility Certain patients/groups have specific susceptibility to ADRs Could be due to : Age Gender Disease states Physiological states
80

Phase 2 (24 decks)

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