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Introductory Clinical Sciences > Introduction To Pharmacology Lecture Block 14.11.23 > Flashcards

Introduction To Pharmacology Lecture Block 14.11.23 Flashcards

1
Q

Define pharmacology

A

‘The study of how medicines work and how they affect our bodies’ (British Pharmacological Society)

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2
Q

Define pharmacodynamics

A

The biochemical, physiological and molecular effects of a drug on the body

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3
Q

Define pharmacokinetics

A

The fate of a chemical substance administered to a living organism

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4
Q

What is the pharmacokinetic processes?

A

A - Absorption
D - Distribution
M - Metabolism
E - Excretion

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5
Q

Describe absorption (pharmacokinetics)

A

Transfer of a drug molecule from site of administration to systemic circulation

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6
Q

In which 2 methods of administration does 100% of the dose reach systemic circulation?

A

IV (intravenous) and IA (intra-arterial)

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7
Q

What are the 10 ways where drugs must cross at least one membrane to reach systemic circulation?

A

IM (intramuscular)
SC (subcutaneous)
PO (oral)
SL (sublingual)
INH (inhaled)
PR (rectal)
PV (vaginal)
TOP (topical)
TD (transdermal)
IT (intrathecal)

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8
Q

What are the 3 mechanisms for drugs to permeate membranes?

A

Passive diffusion through hydrophobic membrane —> lipid soluble molecules

Passive diffusion aqueous pores —> very small water soluble drugs (eg lithium), most drug molecules are too big

Carrier mediated transport —> Proteins which transport sugars, amino acids, neurotransmitters and trace metals (and some drugs)

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9
Q

What are the 2 factors affecting drug absorption?

A
  1. Lipid solubility
  2. Drug ionisation
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10
Q

What is pKa?

A

The value at which the ionised and unionised form of the drug are equal (50:50)

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11
Q

Where are weak acids best absorbed?

A

In stomach

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12
Q

Where are weak bases best absorbed?

A

Small intestine

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13
Q

What is drug ionisation?

A

Drugs going from ionised to unionised)

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14
Q

What are 5 factors affecting oral drug absorption in stomach

A

Gastric enzymes - drug molecule may be digested (peptides, proteins) —> Eg. insulin and biologicals

Low pH - molecule may be degraded (benzylpenicillin)

Food (full stomach will generally slow absorption)

Gastric motility (altered by drugs and disease state)

Previous surgery (eg gastrectomy)

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15
Q

What are 3 factors affecting oral drug absorption in small intestine?

A

Drug structure —> Lipid soluble/unionised molecules diffuse down concentration gradient, large or hydrophilic molecules are poorly absorbed

Medicine formulation —> Capsule/tablet coating can control time between administration and drug release, modified release controls (slows) the rate of absorption (less frequent dosing)

P-glycoprotein —> Substrates are removed from intestinal endothelial cells back into lumen

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16
Q

What is first pass metabolism?

A

metabolism of drugs preventing them reaching systemic circulation

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17
Q

Define bioavailability

A

Proportion of administered dose which reaches the systemic circulation

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18
Q

What are the ways which first pass metabolism may occur?

A

Degradation by enzymes in intestinal wall

Absorption from intestine into hepatic portal vein and metabolism via liver enzymes

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19
Q

Is the degree of first pass metabolism the same in each person?

A

No, it differs in each person

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20
Q

How can you avoid first pass metabolism

A

Avoid giving via routes that avoid splanchnic circulation (e.g. rectal)

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21
Q

What 2 factors is bioavailability dependant on?

A

Dependent on extent of drug absorption and extent of first pass metabolism

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22
Q

Is bioavailability affected by rate of absorption?

A

NO

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23
Q

How is bioavailability expressed?

A

% or fraction

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24
Q

What 2 ways does bioavailability vary?

A

Route of administration

Between individuals

25
Q

What are 3 pros of rectal administration?

A

Local administration

Avoids first pass metabolism

Nausea and vomiting

26
Q

What are 2 cons of rectal administration

A

Absorption can be variable

Patient preference

27
Q

2 pros of inhaled administration

A

Well perfused large surface area

Local administration

28
Q

1 con of inhaled administration

A

Inhaler technique can limit effectiveness

29
Q

2 pros of sub-cutaneous administration

A

Faster onset than PO

Formulation can be changed to control rate of absorption

30
Q

1 con of sub-cutaneous administration

A

Not as rapid as IV

31
Q

2 pros of trans-dermal administration

A

Provides continuous drug release
Avoids first pass metabolism

32
Q

2 cons of trans-dermal administration

A

Only suitable for lipid soluble drugs
Slow onset of action

33
Q

What are the 4 compartments of the body where drugs can be distributed in?

A

Fat
Plasma
Interstitial fluid
Intracellular fluid

34
Q

What 3 things will influence ability to move between compartments?

A

Molecule size, lipid solubility, protein binding

35
Q

Small molecule size effect on distribution?

A

Increased distribution

36
Q

Large molecule size effect on distribution?

A

Decreased distribution

37
Q

Hydrophilic molecule effect on distribution?

A

Decreased distribution

38
Q

Lipophilic molecule effect on distribution?

A

Increased distribution

39
Q

Increased protein bound molecules effect on distribution?

A

Decreased distribution

40
Q

Decreased protein bound molecules effect on distribution?

A

Increased distribution

41
Q

Define volume of distribution (Vd)

A

Theoretical volume a drug will be distributed in the body (apparent volume of distribution) and volume of plasma required to contain the total administered dose

42
Q

Will well distributed or poorly distributed drugs have a high Vd?

A

well distributed drugs will have high Vd

43
Q

What are the 3 ways for drugs to reach the CNS?

A

High lipid solubility. e.g. Ѱ drugs usually very lipid soluble (therefore large Vd)

Intrathecal administration (e.g. baclofen in MS and spinal cord injury, chemotherapy)

Inflammation (causes barrier to become leaky)

44
Q

Define drug elimination

A

the process by which the drug becomes no longer available to exert its effect on the body

45
Q

What are the 2 phases of drug metabolism

A

Phase 1: Oxidation/reduction/hydrolysis to introduce reactive group to chemical structure

Phase 2: Conjugation of functional group to produce hydrophilic, inert molecule

46
Q

What cytochrome is responsible for majority of phase 1 metabolism?

A

Cytochrome P450 (CYP450)

47
Q

Where is Cytochrome P450 (CYP450) mostly located?

A

Liver (extrahepatic: small intestine, lung)

48
Q

What 3 ways can CYP function vary?

A

Genetic variation

Reduced function in severe liver disease

Interactions enzyme inhibiting/inducing drugs or food can reduce/increase enzyme activity

49
Q

What drug molecules will readily cross hepatocytes membrane? What does it produce?

A

Lipophillic unbound drug molecules. Produces a reactive metabolite by creating or unmasking a reactive functional group.

50
Q

What are the 5 most significant CYP enzymes for drug metabolism?

A

3A4, 2C9, 2C19, 1A2, 2D6

51
Q

How many CYP450 enzymes are there?

A

57

52
Q

What is phase II metabolism

A

Conjugation of an endogenous functional group (glycine, sulfate, glucuronic acid) to produce a non-reactive polar (therefore hydrophilic) molecule, Hydrophyllic metabolite can then be renally excreted.

53
Q

What 3 ways can drugs and metabolites be excreted?

A

Liquids (small, polar molecules): urine, bile, sweat, tears, breast milk

Solids (large molecules): faeces (through biliary excretion)

Gases (volatiles): expired air

54
Q

What are the 3 processes which account for renal excretion of drugs?

A
  1. Glomerular filtration
  2. Active tubular secretion
  3. Passive reabsorption
55
Q

How are drugs excreted in glomerular filtration?

A

20% of plasma filtered
Free/unbound drug molecules filtered
Very large molecules excluded

56
Q

How are drugs excreted in active tubular filtration?

A

80% of renal blood flow passes on to peritubular capillaries

Drug molecules transported by carrier systems —> Organic anion transporter (OAT) and organic cation transporter (OCT)

Can clear protein bound drug

Most effective renal clearance mechanism

57
Q

How are drugs excreted in passive reabsorption?

A

Diffusion down the concentration gradient from tubule into peritubular capillaries

Hydrophobic drugs will diffuse easily

Highly polar drugs will be excreted

58
Q

What can reduced kidney function lead to (in terms of drug clearance)?

A

Kidneys excrete drugs and drug metabolites (active and inactive)

Reduced kidney function can lead to accumulation and toxicity of renally cleared drugs

Introductory Clinical Sciences (44 decks)

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