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Block 1 > Pharmacology, Prescribing And Therapeutics > Flashcards

Pharmacology, Prescribing And Therapeutics Flashcards

1
Q

What is clinical pharmacology?

A

Science of drugs + their use in humans

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2
Q

What is a drug?

A

A molecule which has a physiological effect when ingested or otherwise introduced into the body; size + chemical nature of modern drugs can vary greatly (e.g. small compounds ~500Da -> Abs ~150,000Da)

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3
Q

Define bioavailability.

A

The proportion of administered drug which reaches the systemic circulation unchanged + is thus available for distribution to the site of action

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4
Q

What is the bioavailability of intravenous (IV) injection? Why?

A

100% because all the drug reaches the systemic circulation unchanged

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5
Q

What are the pros and cons of intravenous (IV) injection?

A

Pros: rapid + powerful action

Cons: inconvenient for long-term therapy

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6
Q

Why is the bioavailability of the oral route? Why?

A

< 100% due to:

  • Exposure to pH, enzymes + microbial activity in gut
  • Exposure to 1st pass metabolism
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7
Q

What are the pros and cons of the oral route?

A

Pros: popular, often safest, most convenient + economical

Cons: absorption depends on rates of GI transit + requires patient compliance

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8
Q

What different mucosal routes can drugs be administered by?

A 
Sublingual/buccal
Nasal
Eye
Vaginal
Rectal
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9
Q

Why are mucosal routes of drug administration good?

A

Achieves rapid transit to systemic circulation

Avoids 1st pass metabolism

Drug stability as pH in mouth is neutral compared to acidic stomach

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10
Q

What can the inhalation route of drug administration be used for?

A

Aerosols for airway disease

Lipid soluble anaesthetics

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11
Q

Why is the inhalation route of drug administration good?

A

Rapid absorption

Avoids 1st pass metabolism

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12
Q

What is the problem with the transdermal route of drug administration? How can this problem be avoided?

A

Outer skin layer influences rate of absorption

Low input rates can be useful instead for e.g. HRT (oestrogen/progesterone)

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13
Q

How does subcutaneous injection work?

A

Consistent absorption from small volumes e.g. insulin in which there is passive diffusion into bloodstream via absorption across capillary walls

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14
Q

Why are intramuscular injections a good route of drug administration?

A

Large blood in muscles of upper arm

Reliable + suitable for irritant drugs

Good for depot preps (long lasting)

Rapid absorption of larger volumes in contrast to subcutaneous injection

Absorption is perfusion limited i.e. increased with exercise

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15
Q

Define pharmacokinetics (PK).

A

The study of drug movement within the body i.e. what the body does to a drug

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16
Q

Define pharmacodynamics (PD).

A

The study of drug effects + mechanisms of action i.e. what the drug does to the body

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17
Q

What are the 4 phases of pharmacokinetics (PK)?

A
  1. A: absorption
  2. D: distribution
  3. M: metabolism
  4. E: excretion
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18
Q

Explain the first phase of pharmacokinetics (PK)?

A

Absorption: crossing of the GI tract + avoidance of metabolism by the liver/GI tract - most drug absorption happens via PASSIVE + in SI (lipid solubility affects absorption rate)

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19
Q

What is the equation for rate of diffusion?

A

Permeability x SA x concentration difference

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20
Q

What factors affect GI drug absorption rates?

A

SA/blood flow

GI motility; affected by drugs or pathophysiological/psychological states

Malabsorptive states e.g. coeliac disease

Food type; meal composition (fat intake delays gastric emptying) + specific drug-food interactions (e.g. dairy + tetracycline)

21
Q

Define first pass metabolism.

A

The extent of metabolism occurring before the drug enters the systemic circulation

22
Q

What organs and tissues are involved in first pass metabolism?

A

Gut lumen e.g. gastric acid

Gut wall enzymes

Liver (MOST IMPORTANT)

23
Q

Why is insulin not taken orally?

A

Inactivated by gastric acid + proteolytic enzymes of the gut lumen

24
Q

What occurs in first pass metabolism?

A

Drugs enter digestive system, hepatic portal system + liver where they can be rapidly metabolized by enzymes - can greatly reduce levels reaching systemic circulation + thus, bioavailability

25
Q

Explain the second phase of pharmacokinetics (PK).

A

Distribution: process by which drug is transferred from systemic circulation into tissues

26
Q

What factors determine the rate and extent of drug distribution?

A

Ability of drug to pass through tissue membranes

Lipid solubility of drug i.e. increases distribution

Binding of drug to plasma proteins

Active transport of some drugs across cell membranes

Presence of other drugs in the body

Perfuse rate limitations i.e. regional blood flow

27
Q

Explain how drug binding to plasma proteins can affect its distribution in the body.

A

Drugs can reversibly + non-specifically bind to plasma proteins e.g. albumin w/o significant effects on protein function

But, only non-protein-bound drug traverses membrane to gain access to cells

So changes in protein binding can lead to changes in drug distribution (high protein binding can increase drug T1/2)

28
Q

What is the criteria for plasma protein binding significantly altering drug distribution?

A

Protein-bound drug constitutes 90% of total drug in plasma

Extent of distribution of drug to tissues must be small

29
Q

Give an example of why plasma protein binding of drugs is important.

A

Warfarin is taken long-term + is normally 99
% protein-bound

Aspirin is also a high protein binder that displaces warfarin from proteins

So increased plasma levels of unbound warfarin which increase its biological effects + can pose risk (withdrawal of aspirin will have opposite effect also posing risk)

30
Q

What is the major site of drug metabolism? Where else does this occur?

A

LIVER

GI tract, kidneys, skin

31
Q

What are the 2 phases of drug metabolism? Describe them.

A

Phase 1 e.g. oxidation, reduction, hydrolysis: products produced chemically more reactive + often more toxic than parent drug

Phase 2 e.g. conjugation: conjugates are chemically polar + readily cleared by kidneys or excreted in bile

32
Q

What is the difference usually between the drug metabolites and the drug itself?

A

Drug metabolites exhibit less biological activity + more easily removed from plasma than the original form of the drug

33
Q

What are the 3 fates of drugs that go through drug metabolism?

A
  1. Conversion to inactive compounds (most common) - if this occurs in liver, it promotes excretion via kidneys
  2. Become active pro-drugs with altered absorption kinetics - prevents adverse effects + improves distribution
  3. Active metabolites e.g. codeine (inactive) -> morphine (active)
34
Q

What factors affect drug metabolism?

A

Liver disease

Age

Genetic polymorphisms in drug metabolising enzymes (pharmacogenetics)

Competition between different drugs for the same metabolising enzyme

35
Q

What is the major route of drug excretion? What others exist?

A

KIDNEYS

GI: bile into intestine (may be reabsorbed via enterohepatic circulation) OR faecal

Lungs, sweat, tears, saliva + breast milk too

36
Q

Whats special about drugs like digoxin in terms of excretion?

A

Excreted unaltered

37
Q

Define half-life (T1/2).

A

The time it takes for the plasma [drug] to halve irrespective of the starting dose

38
Q

Why is it important to understand drug half-life (T/12)?

A

Guide to time it takes for a drug to be eliminated from body

Guide to rate of accumulation of drug in body during multiple dosing; time to steady state (may be altered in kidney impairment)

Guide to calculating loading dose during treatment

39
Q

What conjugation reactions can be involved in phase 2 drug metabolism?

A

Sulphonation
Gluocoronidation
Methylation
Acetylation

40
Q

What are the 4 ways in which drugs can exert their effect on the body?

A
  1. Direct effects on cellular receptor function
  2. Action on ion channels
  3. Action of membrane transport processes
  4. Enzyme inhibition
41
Q

What are receptors?

A

Specific proteins with distinct binding sites + signal transduction properties situated in cell membranes (fast responses i.e. secs) or within cell cytoplasm (slower responses i.e. hrs/dys)

42
Q

What different types of ligands exist for receptors?

A

Agonists
Antagonists
Partial agonists

43
Q

How can drugs exert their effect by acting on ion channels?

A

Ion channels influence movement of ions (e.g. Na+, K+, Ca2+ & Cl-) in + out of cell across membrane which influences polarisation of excitable cell membranes + IC signalling cascades so drugs acting on ion channels affect neural transmission + SM contractility

44
Q

What are some examples of drugs that target ion channels?

A
  1. Na channel blockers in local anaesthesia e.g. lidocaine

2. Ca channel blockers to slow HR e.g. verapamil

45
Q

How can drugs exert their action by targeting transporter function?

A

Transporters mediate movement of specific endogenous signalling molecules + nutrients in + out of cells e.g. neurotransmitters + glucose

46
Q

What is an example of a drug that targets transporter function?

A

The SSRI fluoxetine (Prozac) blocks the neuronal SERT leading to retention of 5-HT in neural synaptic cleft

47
Q

What are some examples of drugs that target enzymes?

A
  1. ACE inhibitors block ACE

2. NSAIDs block COX-2

48
Q

What are the 2 effects drugs can have on enzymes?

A
  1. Reaction

2. Inhibition

Block 1 (54 decks)

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