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IMS Week 7 > Lecture 34 & 35 - Introduction to Pharmacology and pharmacokinetics concepts > Flashcards

Lecture 34 & 35 - Introduction to Pharmacology and pharmacokinetics concepts Flashcards

1
Q

what is Pharmacology

A

effects of chemicals on biological entities
interaction of drugs biologically
effect of drugs
therapeutic an toxic effects

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2
Q

pharmacodynamics

A

specific to drug or drug class

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3
Q

pharmacokinetics

A

non-specific general processes

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4
Q

advantages and disadvantages of oral route of administration

A

convenient, safe, economical

cannot be used for drugs inactivated by 1st pass metabolism or that irritate the gut

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5
Q

advantages and disadvantages of intramuscular

A

suitable for suspensions and oily vehicel
rapid absorption from solutions
slow and sustained absorption from suspensions

dis - may be painful, cause bleeding at site of infection

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6
Q

subcutaneous - advantages and disadvantages

A

suitable for suspensions and pellets
cannot be used to deliver large volumes of fliof
cannot be used for drugs that irritate cutaneous tissue

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7
Q

intravenous - advantages and disadvantages

A

bypass absorption yielding immediate effect

  • 100% immediate bioavailibity
  • poses more risk for toxicity
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8
Q

buccal - advantages and disadvantages

A

rapidly absorbed
avoids 1st pass metabolism

dis - effect only for low doses
drugs must be water and lipid soluble

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9
Q

transdermal

A

avoids 1st pass metabolism, effective only for low doses of drug that are highly lipid soluble

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10
Q

inhalation

A

produces a localised effect
drug particles must be correct size
dependent on patient technique

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11
Q

intrathecal

A

local and rapid effects
requires expert administration
may introduce infection/toxicity

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12
Q

epidural

A

provides a targeted effect

risk of failure, risk of infection

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13
Q

topical

A

non-invasive and easy to administer

poor lipid soluble not absorbed via skin or mucous membranes
very slow absorption

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14
Q

types of oral preparations

A

tablet - compressed powder - can be coated to protect against stomach acid
capsule - solid dosage enclosed by gelatin shell
solution - dissolved in solvent
suspension - suspended in a vehicle - large amounts of drug

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15
Q

what processes are involved in pharmacokinetics

A

ADME - Absorption

distribution, metabolism and excretion

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16
Q

What is absorption

A

transfer of drug from site of administration into general or systemic circulation

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17
Q

What are the factors that affect oral absorption

A

needs to disintegrate and dissolve in the GIT content to form a solution before becoming absorbed

need to be lipid soluble to be absorbed by the gut

rate of gastric emptying determines the rate at which a drug is delivered to the small intestine.

physiochemical factors - drug-food interactions - insoluble complexes

presence of food may delay absorption
-reduce adverse effects of certain medicine eg. NSAID’s

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18
Q

what is the effect of pH on drug absorption

A

increase in pH leads to an increase in ionisation
acid - increasingly ionised
bases - increasingly unionised

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19
Q

What nature of the cell membrane allows drugs to cross the cell membrane?

A

the cell membrane has a lipophilic nature

only permits passage of uncharged fraction of any drug

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20
Q

What is distribution

A

drug is transferred reversibly from general circulation into tissues as concentrations in blood increase

from tissues into blood as concentrations in blood decrease

occurs by passive diffusion of un-ionised form across cell membrane

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21
Q

what happens to distribution after an IV injection

A

high plasma concentration and drug rapidly equilibrates with well perfused tissue giving relatively high concentrations in these tissues

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22
Q

Different types of drug movement

A

bulk flow transfer - blood transfer
diffusion transfer - molecule by molecule - short distances
lipid solubility - passive diffusion
carrier mediated transfer

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23
Q

What are the factors affecting drug distribution

A

Plasma protein binding - competition
specific drug receptor sites in tissues
regional blood flow - reduced and enhanced blood flow

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24
Q

how does lipid solubility and disease affect distribution?

A

lipid solubility - blood/brain barrier, membrane of GI tract eg, vancomycin, highly water soluble drugs eg. gentamycin

disease - liver disease can low plasma protein levels

renal disease - cause high blood urea levels

25
Q

What happens in drug-protein binding

A

binding of drugs with albumin and glycoproteins

when a patient takes a drug that becomes highly protein bound when they are already taking a drug that is highly protein bound, the drug is displaced and increase in unbound concentrations of drug and activity

26
Q

Albumin bound proteins

A

furosemide, ibuprofen, phenytoin, thiazides, warfarin

27
Q

Glycoprotein bound

A

chlorpromazide, propranolol, tricyclic anti-depressants, lidocaine

28
Q

what molecules can cross a cell membrane

A

those not bound to protein

they are crossed by:
passive diffusion - high conc to low conc across ion channels
transporters - 
membrane pores
vesicle mediated transport
29
Q

What is facilitated diffusion

A

combine with membrane bound carrier protein
movement still dependent on conc gradient
faster than passive diffusion

30
Q

What is active transport

A

requires energy

molecule transported against conc gradient

31
Q

How can molecules be transported by pinocytosis

A

molecules engulfed by cell membrane and vesicle is formed

vesicle moved into cell

molecule is released within cell

32
Q

distribution to specific organs - brain?

A

blood brain barrier protects it from toxic chemicals

only lipid soluble can enter

33
Q

What is the functional basis of the blood brain barrier

A

reduced capillary permeability
tight junctions between endothelial cells
decrease in size and pores in cell membranes
presence of surrounding astrocytes
efflux transporters - return drugs back to circulation

34
Q

How does distribution work in a foetus?

A

cross placenta

placental blood flow is low compared to other organs - equilibriate slowly with maternal concentrations

highly polar and large
molecules dont cross

foetal liver - lower conc of metabolising enzymes

maternal elimination - processes foetal concentrations of drugs

effect of drugs given to mother close to delivery produce prolongued effect on a new born

35
Q

what are the 4 aspects of drug metabolism?

A

Activation of inactive drug
Production of active drug with increased activity from active drug
Inactivation of active drugs
Change in the nature of the activity

36
Q

Factors affecting drug metabolism

A 
first pass effect
hepatic blood flow
liver disease
genetic factors -acetylation status
other drugs
age (impaired hepatic enzyme activity) - elderly and children below 6 months
37
Q

First pass metabolism

A

stomach, SI, LI and lungs
- oral and inhalation
occurs prior to and during absorption
intestinal lumen - digestive enzymes secreted by the mucosal cells and pancreas. some break down proteins so are not absorbed
intestinal wall - rich in enzymes - further metabolism
liver - major site
lung - high affinity for many drugs and are the site for many local hormones

38
Q

Describe the 2 phases of metabolism?

A

Phase 1 - oxidation, reduction and hydrolysis
form more reactive products, sometimes toxic (lipophilic - fat soluble)
Phase 2 - conjugation
usually form inactive and readily excretable products (becomes hydrophilic water soluble to be excreted)

39
Q

Cytochrome PF50

A

Large family of enzymes and individual one is called isoenzyme
different types of cyt P450

40
Q

Paracetamol poisoning

A

predominantly metabolised by Phase 2 metabolism

when overdosed - phase 2 becomes too saturated

body tries to metabolise through oxidation (phase 1 mechanism) - produces toxic metabolite - n-acetyl-p benzoquinone imine
damages kidneys and liver

41
Q

Antidote for paracetamol poisoning and how?

A

n-acetylcysteine enhances phase 2 metabolism

42
Q

DRUGS THAT UNDERGO SUBSTANTIAL FIRST PASS METABOLISM

A 
Aspirin
Glyceryl trinitrate
Levodopa
Lidocaine
Morphine
Propanolol
Salbutamol
Verapamil
43
Q

ENZYME INDUCING DRUGS

A

Enhance the production of liver enzymes which break down drugs

Faster rate of drug breakdown

Larger dose of affected drug needed to get the same clinical effect

44
Q

examples of enzyme inducing drugs

A 
Phenytoin
Phenobarbitone
Carbamazepine
Rifampicin
Griseofulvin
Chronic alcohol intake
Smoking
45
Q

ENZYME INHIBITING DRUGS

A

Inhibit the enzymes which break down drugs

Decreased rate of drug breakdown

Smaller dose of affected drug needed to produce the same clinical effect

46
Q

BIOAVAILABILITY

A

Bioavailability is the proportion of a dose which actually gets into the systemic circulation

47
Q

factors affecting bioavailablity

A

Pharmaceutical Preparation
Particle size, composition of formulation

  1. Physicochemical Interactions
    Other drugs or food may interact with or inactive the drug
  2. Patient Factors
    Malabsorption syndromes, gastrointestinal motility
  3. Pharmacokinetic interactions and first-pass metabolism
48
Q

Clerance of a drug

A

This is the measure of the removal of drug from the body or the volume of plasma completely emptied of drug per unit time

This includes metabolic as well as renal and biliary clearance

Clearance does not indicate the amount being removed but the volume of plasma (or blood) from which the drug is completely removed or cleared in a given time period.

49
Q

half life of a drug

A

take taken for concentration to reduce by half

50
Q

What is half life increased by?

A

Diminished renal plasma flow e.g. heart failure

Addition of a second drug that displaces the first from albumin thereby increasing the volume of distribution of the drug

Decreased extraction ratio as seen in renal disease

Decreased metabolism as seen in liver disease

51
Q

drug elimination

A

fluids - urine, bile, sweat, tears, milk
solids - hair, faeces
gases - important for volatile compounds

52
Q

Elimination via the kidney

A
  1. free drug enters GF
  2. Active secretion in PCT
  3. Passive reabsorption of lipid soluble, unionised drug - DCT
  4. Ionised lipid insoluble drug into urine
53
Q

What does elimination via the kidney depend on

A

blood flow to kidney
GFR
Active secretion of drugs into tubule at the start
passive reabsorption back into the tubule

54
Q

SIGNIFICANCE OF ALTERED RENAL FUNCTION

A

Care with renally excreted drugs

Care with drugs with a narrow therapeutic index
Example: digoxin

Care with drugs which produce active metabolites

Care with drugs that may further reduce renal function

55
Q

what is used to evaluate renal function

A

creatinine - produced by muscle

estimation of creatinine clearnace estimates clearance of drugs filtered at glomerulus

56
Q

COCKCROFT GAULT EQUATION

A

Estimated Creatinine Clearance in mL/min
= (140-Age) x Weight x Constant
Serum Creatinine

57
Q

egfr

A

eGFR uses serum creatinine, age, sex and race (for African-Caribbean patients)

This is normalised to a body surface area of 1.73m2 and derived from a specific formula.

Absolute GFR = eGFR x individual’s body surface area /1.73

58
Q

drug monitoring

A

clinical effectMeasuring BP, pain reduction etc
biological effect - prothrombin time for warfarin, glucose for insulin etc
plasma concentrations when relevant

59
Q

Therapeutic index

A

ratio of:
Dose that causes toxicity
Dose that produces desired effect

efficacy vs toxicity

IMS Week 7 (4 decks)

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