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HSC2008 Pathophysiology & Pharmacology > Basic Pharmacology > Flashcards

Basic Pharmacology Flashcards

1
Q

What is the meaning of “Pharmacology”?

A

Study of how a drug affects the biological system & how the body responds to the drug

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2
Q

What is the meaning of “Pharmacodynamics”?

A

Study of what the drug does to the body

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3
Q

What is the meaning of “Pharmacokinetics”?

A

Study of what the body does to the drug

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4
Q

What is the meaning of “Pharmacogenomics”?

A

Study of the role of genomes in drug response

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5
Q

What are the principles of pharmacodynamics?

A

Downstream signaling - process where a signal is transmitted by a receptor / effector molecule to activate intracellular signalling events; lead to changes in
- gene expression
-protein activity
- cellular behaviour

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6
Q

What are the concepts of receptors?

A
  1. Responsible for the selectivity of drug actions
  2. Determine the quantitative relations concentration of drugs & it’s effects (high receptor affinity = lower concentration of drug dose required to Brin about action)
  3. Mediate the action of Pharma-antagonists
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7
Q

What are the different drug types leading to different effects?

A
  • Agonist - regulate the function of receptors & activates it
  • Antagonist (competitive) - share the same receptor site as endogenous molecule; block agonist from binding to receptors
  • Allosteric activator - increase affinity of receptors leading to enhanced activity
  • Antagonist (non-competitive) - bind to different receptor site from agonist leading to inhibition of activity
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8
Q

What are the different ways to classify drugs?

A
  • Indication - what is the drug used for
  • Chemical structures - agonist. antagonist, etc)
  • Mechanism of actions (what is it’s effect)
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9
Q

What is the clinical use of Clopidogrel?

A

Action - platelet inhibitor; used to reduce the risk of MI infection / stroke

  • irreversibly inhibits P2Y12 which is a subtype of ADP receptor
  • P2Y12 is required for platelet activation & cross-linking of fibrin
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10
Q

What is the side effects of using Clopidogrel?

A
  • excessive bleeding
  • secondary to inhibitory effect on platelet function
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11
Q

What are the 4 principles of pharmacokinetic principles?

A

Absorption, Distribution, Metabolim, Excretion

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12
Q

What is the definition of Bioavailability?

A

The amount to unchanged drug that reached the systemic circulation after administration; the extent of drug absorption

  • BA differs with the route of administration
  • IV BA 100%
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13
Q

What are the main modes of absorption?

A
  • Passive diffusion
  • Facilitated passive diffusion
  • Active diffusion
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14
Q

What is the first pass effect?

A

Drugs that is metabolised at a specific location in the body (mostly liver), resulting in a reduced concentration of the active drug upon reaching it’s site of action / systemic circulation

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15
Q

What are the factors affecting drug absorption?

A

Drug factors
- Degree of ionization
- Lipid solubility
- Molecule size
- pKa (higher pKa = lower pH)
- Stability in gastric acid

Patient factors
- Area of absorptive surface
- Gut pH
- Gut motility
- Presence of food or other drugs

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16
Q

What is Volume of distribution (Vd)?

A

The amount of drug in the body in relation to the concentration in the plasma / blood

  • High Vd = drug going into tissues & organs; little stay in blood
  • Low Vd = drug staying in blood; does not go to organs / tissues
17
Q

How does protein affect drug distribution?

A

Drugs can bind to proteins

  • Higher % of drug binding to proteins = smaller Vd
18
Q

What are the factors affecting drug distribution?

A

Drug factors
- Degree of ionization
- Lipid solubility
- Molecule size
- Protein binding
- Partition coefficient

Patient factors
- Fat & water content
- Protein level
- Disease status
- Concomitant drugs

19
Q

What is the meaning of Biotransformation?

A

It refers to the metabolisation of drugs into a more hydrophilic form for it to be cleared by the kidneys

  • Most metabolism occurs in the liver
20
Q

What are the 2 main enzymatic phases?

A

Phase 1 - reaction of functionalization
- creating a functional group / modification of existing group (i.e. oxidation, reduction, hydrolysis)
- typically involves CYP450 enzymes (heme-containing)
- CYP3A4 is the most prevalent
- CYP enzymes helps to breakdown non-drug compounds (alcohol by CYP2E1)

Phase 2 - reaction of conjugation
- coupling a drug with endogenous molecule to make it more hydrophilic
- Eg. of molecules - glucuronidation, Sulphation, acetylation

21
Q

What are the factors affecting drug metabolism?

A

Drug delivery factors
- blood flow to liver
- protein binding

Intrinsics factors
- metabolising capacity depending on genetics
- concomitant interacting drugs
- genetic polymorphism - presence of 2 or > variants of a specific DNA

22
Q

How does drug-drug interaction occur during Phase 1 of biotransformation?

A

Via inhibition / induction of CYP enzymes

Eg. Warfarin + CYP = increase effect of warfarin = increased anticoagulant effect

23
Q

How are drugs excreted?

A

Metabolites & parent drugs are eliminated from the kidneys and excreted in the urine

  • Accumulation of drugs may occur in patients with kidney dysfunction
  • Might need to alter the type of drug / reduce the dosing
24
Q

What is the definition of half-life?

A

The time taken for the concentration of drugs to reduce to half; how fast the drugs can be cleared from the body

  • Shorter T1/2 = faster drug clearance = more frequent dosing
  • Dosing of drugs depends of T1/2
25
Q

What is the clinical use of pharmacokinetics?

A

To aid in the dosing regimen to determine therapeutic index for safe & effective drug dosing

  • How to give (mode of administration)
  • How much to give (dosing)
  • How frequent to give
26
Q

What is therapeutic drug monitoring?

A

Measurement of drug level in blood through drawing patient’s blood; used for drugs with narrow therapeutic index

  • Eg. Warfarin
27
Q

What does a drug’s therapeutic index reflect?

A

The minimum effective concentration & minimum toxic concentration

28
Q

What does EC50 / ED50 refers to?

A

The concentration of drug that produces 50% of it’s clinical effect

  • Lower EC50 = increased drug potency (lesser concentration needed to produce it’s effect)
29
Q

What is the ADME of Clopidogrel?

A
  • Absorption - rapid & complete; BA >90%; not affected by food intake
  • Distribution - Vd is large
  • Metabolism - CYP2C19 required to turn it into active metabolite
  • Excretion - 50% metabolite unchanged in urine
  • T1/2 = 6-8hrs (short)

Variants of gene encoding CYP2C19
- CYP2C191 - normal enzyme activity
- CYP2C192 - no / reduced enzyme activity
- CYP2C19*17 - increased enzyme activity

  • Poor metabolizer (PM) - unable to activate the drug -> higher concentration of Clopidogrel
30
Q

What are the mechanisms for variations in drug responsiveness?

A

Difference in drug concentration that reaches receptor site
- attributed to ADME
- multidrug resistance genes

Variations in concentration of endogenous receptor ligland

Alterations in number / function of receptors
- genetic factors leading to differences in number & function
- drug tolerance (repeated exposure decrease response)

Changes in components of response distal to receptor
- post receptor processes influence of drug response
- age & general health of patient
- severity of disease state
- presence of interacting drug that profane antagonistic effects

31
Q

What are some examples of Genetic Polymorphisms (GP)?

A

Phase 1 (CYP3A4/5)
- Belongs to CYP450
- Metabolises a wide variety of drugs including Tacrolimus (drug used to in organ transplant to prevent rejection)
- Some patient express CYP3A5 genes which increase the metabolism of drugs
- CYP3A5 expressers who went through kidney transplant requires a higher dose of Tacroimus

Phase 2 (TPMT - Thiopurine S Methyltransferase)
- Enzyme responsible for methylation of Thiopurine groups of drugs
- Thiopurine drugs are metabolised by TPMT into TGN
- 3 clinical phenotypes - high, intermediate, low
- Low level of TPMT activity leads to higher risk of toxicity including myelosuppression

Drug induced hypersensitivity reactions
- Routine check for presence of HLA-B1502 before starting patient on Carbamazepine
- Presence of HLA-B5701 (increase risk of Steven-Johnson’s Syndrome) before staring Abacavir

HSC2008 Pathophysiology & Pharmacology (4 decks)

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