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Phase 2a - Conditions > Pharmacology > Flashcards

Pharmacology Flashcards

1
Q

Define Synergy

A

Interaction of drugs such that the total effect is greater than the sum of the individual effects

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2
Q

Define Antagonist

A
  • An antagonist is a substance that acts against and blocks an action
  • (2 drugs opposed to each other)
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3
Q

Define Summation

A
  • Different drugs used together to have the same effect as a single drug would
  • (1+1=1)
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4
Q

Define Potentiation

A
  • Enhancement of one drug by another so that the combined effect is greater than the sum of each one alone (1+1=1+1.5)

(drug interactions can be positive or negative)

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5
Q

What are the risk factors of drugs?

A
  • Narrow therapeutic index
  • Steep dose/response curve
  • Saturable metabolism
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6
Q

Define Pharmacodynamics

A

The effect the drug has on the human body

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7
Q

Define Pharmacokinetics

A

What the body does with the drug

  • the disposition of a compound within an organism)
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8
Q

What are the mechanisms of Pharmacokinetics?

A

Absorption, Distribution, Metabolism, Excretion

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9
Q

Describe the process of Absorption in Pharmacokinetics

A
  • Motility – if the gut has slowed digestion, the drugs won’t work as well (oral contraceptive pill and antibiotics is the most common interaction)
  • The pills mechanism of action is to absorb hormones whereas antibiotics distrupt the normal gut flora increasing flow - reduces the absorption time for the medication
  • Acidity – pH and pKa interactions
  • Solubility
  • Complex formation
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10
Q

Describe the process of Distribution in Pharmacokinetics

A
  • Drugs can go into the proteins, other tissues or the effect site
  • Protein binding
  • If you give 2 highly protein bound drugs, they will make each other strong and increase their effect so you always make sure you know what drugs the patient has taken before giving them new drugs
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11
Q

Describe the process of Metabolism in Pharmacokinetics

A

CYP450

  • Haemoproteins
  • Metabolise many substrates – endogenous and exogenous
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12
Q

Define Inhibition

A
  • Drug A blocks metabolism of drug B, leaving more free drug B in the plasma so it has an increased effect
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13
Q

Define Inhibition

A
  • Drug C induced CYP450 isoenzyme leading to increased metabolism of drug D so it has a decreased effect
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14
Q

Describe the process of Excretion in Pharmacokinetics

A
  • Renal
  • pH dependant
  • Weak bases – cleared faster if urine acidic
  • Weak acids – cleared faster if urine alkali
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15
Q

Describe the pharmacodynamic mechanisms

A
  • Receptor based
  • Agonists
  • Partial agonists
  • Antagonists (Competitive/Non-competitive)
  • Signal transduction (rarer)
  • Physiological systems
    Different drugs that effect different receptors, but in the same physiological system
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16
Q

What are some common drug interactions

A
  • Warfarin (anti-coagulant that can cause bleeding)

- Acute kidney injury – NSAIDs, ACEi

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17
Q

Define a Drug

A

A medicine or other substance which has a physiological effect when ingested or otherwise introduced into the body

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18
Q

What are drug targets?

A

Proteins:

  • Receptors
  • Enzymes
  • Transporters
  • Ion channels
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19
Q

What is a receptor?

A

A component of a cell that interacts with a specific ligand and initiates a change of biochemical events leading to the ligands observed effects

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20
Q

What are the two types of receptors?

A
  • Exogenous – drugs (extrinsic)

- Endogenous – hormones, neurotransmitters (intrinsic)

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21
Q

What is the purpose of a receptor?

A
  • Receptors are the principal means by which chemicals communicate, including neurotransmitters (acetylcholine, serotonin), autacoids (cytokines, histamine) and hormones (testosterone, hydrocortisone)
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22
Q

What can an imbalance of chemical lead to?

A
  • Allergy due to increased histamine

- Parkinson’s due to reduced dopamine

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23
Q

What can an imbalance of receptors lead to?

A
  • Myasthenia gravis; loss of ACh receptors

- Mastocytosis; increased c-kit receptor

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24
Q

What are the different kinds of receptors?

A
  • Ligand-gated ion channel
    (nicotinic Ach receptor)
  • G-protein coupled receptors
    (Ligands include light energy, peptides, lipids, sugars and proteins)
  • Kinase-linked receptors (receptors for growth factors)
  • Cytosolic/nuclear receptors (steroid receptors)
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25
Q

Define Ligand

A

A molecule that binds to another (usually larger) molecule

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26
Q

Define Agonist

A

A compound that binds to a receptor and activates it

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27
Q

Define Antagonist

A

A compound that reduces the effect of an agonist

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28
Q

Define Affinity

A

Describes how well a ligand binds to the receptor

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29
Q

Define Efficacy

A

Describes how well a ligand activates the receptor

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30
Q

What is the main difference between an Agonist and an Antagonist?

A

Agonists have affinity and efficacy, but antagonists have affinity and ZERO efficacy

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31
Q

What are the two types of cholinergic receptors?

A

Nicotinic and Muscarinic

32
Q

What is a Signal Transduction?

A

A basic process involving the conversion of a signal from outside the cell to a functional change within the cell

33
Q

What is Signal Amplification?

A

Increases the strength of a signal

34
Q

Define Tolerance

A

Reduction in drug effect over time due to continuously, repeatedly, high concentrations

35
Q

What is Allosteric modulation?

A
  • When an allosteric ligand binds to a different site on the molecule and prevents the signal from being transmitted
  • Acts like a non-competitive enzyme inhibitor
  • Allosteric site = site which is not an active site
36
Q

What is the RAAS system?

A
  • The renin–angiotensin–aldosterone system (RAAS), is a hormone system that regulates blood pressure and fluid and electrolyte balance, as well as systemic vascular resistance.
  • RAAS increases blood pressure by increasing the amount of salt and water the body retains.
37
Q

What is an enzyme inhibitor?

A
  • An enzyme inhibitor is a molecule that binds to an enzyme and decreases its activity.
  • It prevents the substrate from entering the enzyme’s active site and prevents it from catalysing its reaction.
38
Q

What is an irreversible inhibitor?

A

It reacts with the enzyme and changes it chemically (e.g. via covalent bond formation)

39
Q

What is a reversible inhibitor?

A
  • Binds non-covalently
  • Different types of inhibition are produced depending on whether these inhibitors bind to the enzyme, the enzyme-substrate complex, or both.
40
Q

Why is renin released from the kidneys?

A
  • Renin is released from granular cells of the renal JGA (juxtaglomerular apparatus) in response to 3 factors:
    1) Reduced sodium delivery to the distal convoluted tubule detected by macula densa cells
    2) Reduced perfusion pressure in the kidney detected by baroreceptors in the afferent arteriole
    3) Sympathetic stimulation of the JGA via β1 adrenoreceptors.
  • The release of renin is inhibited by atrial natriuretic peptide (ANP), which is released by stretched atria in response to increases in blood pressure.
41
Q

Describe the RAAS system

A

1) Renin
2) Angiotensinogen
3) Angiotensin I
4) Angiotensin II
5) Aldosterone

  • Renin is released from granular cells in the JGA in the kidneys
  • Angiotensinogen is a precursor protein produced in the liver and cleaved by renin to form angiotensin I.
  • Angiotensin I is then converted to angiotensin II by angiotensin converting enzyme (ACE).

(This conversion occurs mainly in the lungs where ACE is produced by vascular endothelial cells, although ACE is also generated in smaller quantities within the renal endothelium).

  • Angiotensin II exerts its action by binding to various receptors throughout the body.

(It binds to one of two G-protein coupled receptors, the AT1 and AT2 receptors. Most actions occur via the AT1 receptor).

It causes:

  • Arterioles –> Vasoconstriction
  • Kidney –>Stimulates Na+ reabsorption
  • Sympathetic nervous system - Increased release of noradrenaline (NA)
  • Adrenal cortex - Stimulates release of aldosterone
  • Hypothalamus - Increases thirst sensation and stimulates anti-diuretic hormone (ADH) release
  • Angiotensin II acts on the adrenal cortex to stimulate the release of aldosterone - A mineralcorticoid (steroid hormone released from the zona glomerulosa of the adrenal cortex).
  • Aldosterone acts on the principal cells of the collecting ducts in the nephron. It increases the expression of apical epithelial Na+ channels (ENaC) to reabsorb urinary sodium.
  • As a result, increased levels of aldosterone cause reduced levels of potassium in the blood.
42
Q

Give an example of a drug that involves enzyme inhibition as its mechanism of action

A

ACEi - Ace inhibitor - Angiotensin converting enzyme inhibitor

  • This drug is used for the treatment of blood pressure
  • The RAAS system increases blood pressure by increasing the amount of salt and water the body retains
  • Inhibiting ACE (angiotensin converting enzyme), reduces angiotensin II production, which causes a reduction in blood pressure
43
Q

Define Transport

A

When molecules move across a cell membrane to get what they need such as ions, glucose and amino acids

44
Q

Define Active Transport

A

When ions move from a lower concentration to a higher concentration using energy in the form of ATP

45
Q

Give examples of drug and ion transporters

A

Passive:

  • Symporter (cotransporter protein) - Na+, K+, 2CL-, NaCl
  • Channels - Na/Ca/K/Cl

Active:
- ATP-ases – Na/K, K/H

46
Q

What are the three main types of protein ports in cell membranes?

A

1) Uniporters – use energy from ATP to pull molecules in
2) Symporters – use the movement in of one molecule to pull in another molecule against a concentration gradient - (2 substances moving in the same direction)

3) Antiporters – one substance moves against its gradient, using energy from the second substance (mostly Na+, K+ or H+) moving down its gradient
- (2 substances moving in opposite directions)

47
Q

Give some examples of ion channels

A
  • Epithelial (sodium) – heart failure
  • Voltage-gated (calcium, sodium) – nerve, arrhythmia
  • Metabolic (potassium) – diabetes
  • Receptor activated (chloride) – epilepsy
48
Q

What is drug (xenobiotic) metabolism?

A
  • The metabolic breakdown of drugs occurs through specialised enzymatic systems
  • The rate of metabolism determines the duration and intensity of a drug’s pharmacologic action
49
Q

What is the major enzyme involved in drug metabolism

A
  • CYPs (e.g. cP450) are the major enzymes involved in drug metabolism (75%)
  • Most drugs undergo deactivation by CYPs, either directly or by facilitated excretion from the body.
50
Q

Define Pharmacokinetics

A

The action of drugs in the body (absorption, distribution, metabolism, excretion)

51
Q

Define Absorption in pharmacology

A

Thee process of transfer from the site of administration into the general or systemic circulation

52
Q

What are the routes of administration?

A
  • Oral
  • Intravenous
  • Intra-arterial
  • Intramuscular
  • Subcutaneous
  • Inhalational
  • Tropical
  • Sublingual
  • Rectal
  • Intrathecal
  • Most drugs (except IV/IA) must cross at least one membrane from site of generation to general circulation
53
Q

Describe the passage of drugs across membranes

A
  • Passive diffusion through the lipid layer
  • Diffusion through pores or ion channels
  • Carrier mediated processes
  • Pinocytosis
54
Q

What is Drug Ionisation

A
  • Ionization is a basic property of most drugs that are either weak acids or weak bases
  • Ionizable groups are essential for the mechanism of action of most drugs as ionic forces are part of the ligand receptor interaction
  • Ionized form regarded as most water soluble and un-ionised as lipid soluble
55
Q

Define Oral absorption

A
  • Large surface area and high blood flow of small intestine can give rapid and complete absorption of oral drugs.
  • There are a number of obstacles for the drug to overcome before it reaches the systemic circulation:
56
Q

Define Drug structure

A
  • Drugs need to be lipid soluble to be absorbed from gut

- Some drugs unstable at low pH or in presence of digestive enzymes so have to be given by alternative route

57
Q

Define Drug formulation

A
  • The capsule/tablet must disintegrate and dissolve to be absorbed
  • Some formulated to dissolve slowly or have a coating that is resistant to the acidity of the stomach
58
Q

Define Drug formulation

A
  • The capsule/ tablet must disintegrate and dissolve to be absorbed
  • Some formulated to dissolve slowly or have a coating that is resistant to the acidity of the stomach
59
Q

Define Gastric emptying

A
  • Rate of gastric emptying determines how soon a drug taken orally is delivered to small intestine
  • Can be slowed (food/drugs) or speeded up (gastric surgery)
60
Q

Define First Pass Metabolism

A

Drugs taken orally have to pass 4 major metabolic barriers to reach circulation;

  • Intestinal lumen
  • Intestinal wall
  • Liver
  • Lungs
61
Q

What is the benefit of administering drugs intradermally or subcutaneously?

A
  • Avoids barrier of stratum corneum
  • Mainly limited by blood flow
  • Small volume can be given
  • Use for local effect or to deliberately limit rate of absorption
62
Q

Describe Intramuscular Absorption

A
  • Depends on blood flow and water solubility
  • Increase in either enhances removal of drug from injection site
  • Can make a depot injection by incorporating drug into lipophilic formulation which releases drug over days or weeks
63
Q

Describe Inhalational Absorption

A
  • Large SA and blood flow but limited by risks of toxicity to alveoli and delivery of non-volatile drugs
  • Largely restricted to volatiles such as general anaesthetics and locally acting drugs such as bronchodilators in asthma
  • Asthma drugs non-volatile so given as aerosol or dry powder
64
Q

Describe Protein Binding in Pharmacology

A
  • Many drugs can bind to plasma or tissue proteins
  • This may be reversible or irreversible
  • The most common reversible binding occurs with the plasma protein albumin
  • Binding lowers the free concentration of drug and can act as a depot releasing the bound drug when the plasma concentration drops through redistribution or elimination
  • Some drugs bind irreversibly and cannot re-enter the circulation and is equivalent to elimination
65
Q

Define Drug Distribution

A
  • Lipid soluble drugs easily pass from blood to brain
  • The brain does little metabolizing and drugs are removed by diffusion into plasma, active transport in the choroid plexus or elimination in the CSF
  • Lipid soluble drugs readily cross placenta
  • Large molecules do not cross placenta
  • Foetal liver has low levels of drug metabolizing enzymes, so relies on maternal elimination
66
Q

Define Drug Elimination

A
  • The removal of a drugs activity from the body
  • May involve metabolism – the transformation of the drug molecule into a different molecule
  • Excretion – the molecule is expelled in liquid, solid or gaseous waste
67
Q

Define Drug Metabolism

A
  • Necessary for the elimination of lipid-soluble drugs
  • They are converted to water soluble products that are readily removed in the urine (if they remained lipid soluble they would be reabsorbed)
  • Metabolism produces one or more new compounds which may show differences from the patent drug
  • Drug metabolism may be divided into two phases
68
Q

What are the two phases of Drug Metabolism?

A
  • Phase 1 – these reactions involve the transformation of the drug to a MORE POLAR metabolite
    done by unmasking or adding a functional group -
    oxidations are the commonest reactions catalyzed by CP450
  • Phase 2 – involves the formation of a COVALENT BOND between the drug or its phase 1 metabolite and an endogenous substrate
  • Resulting products are usually less active and readily excreted by the kidneys
69
Q

How are drugs and metabolites excreted?

A
  • Drugs and metabolites are excreted in;
    1) Fluids
  • Important for low molecular weight polar compounds (urine, bile, sweat, tears, breast milk)
  • Urine excretion: Total excretion = glomerular filtration + tubular secretion – reabsorption
    2) Solids – faecal elimination
    3) Gases – expired air important for volatiles
70
Q

Define First order Kinetics in pharmacology

A
  • A drug given IV is rapidly distributed to the tissues
  • By taking repeat plasma samples, the fall in the plasma concentration with time can be measured
  • Often, the decline is exponential - a constant fraction of the drug is eliminated per unit of time
71
Q

Define Zero order Kinetics in pharmacology

A
  • If an enzyme system that removes a drug is saturated the rate of removal of the drug is constant and unaffected by an increase in concentration
  • Linear concentration/time graph
  • Ethanol follows zero order kinetics once alcohol dehydrogenase has been saturated
72
Q

Define Half-Life in pharmacology

A
  • The time taken for a concentration to reduce by one half
  • Elimination rate from the plasma
  • Calculated by time/2
73
Q

Define Distribution

A
  • Rate and extent of movement of a drug into tissues from blood
74
Q

Compare the Distribution of Water soluble drugs and Lipid soluble drugs

A
  • Water soluble drugs rate of distribution depends on rate of passage across membranes
  • Lipid soluble drugs rate of distribution depends on blood flow to tissues that accumulate the drug
75
Q

What is the measure of distribution

A
  • This measure is the apparent volume of distribution

- Vd = the total amount of drug in body (dose)/ plasma concentration

76
Q

Define Clearance

A
  • The volume of blood or plasma cleared of drug per unit time
  • E.g. if 10% of a drug carried to the liver is cleared at a flow rate of 1000ml/min, the clearance is 100ml/min
77
Q

What would happen if the drug clearance was 0?

A
  • If clearance was zero – drug would not be removed and the plasma concentration would remain at equilibrium indefinitely

Phase 2a - Conditions (8 decks)

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