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phar24 > week 3 > Flashcards

week 3 Flashcards

1
Q

define drug elimination

A

when a drug is irreversibly removed from the body, can happen via metabolism or excretion

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2
Q

define drug metabolism/biotransformation

A

= the process of chemical modification of drugs usually by enzymatic reaction within the body

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3
Q

define catabolic reaction

A

breakdown

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4
Q

define anabolic reaction

A

synthesis

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5
Q

two main organs involved in elimination

A

liver & kidney

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6
Q

define prodrug

A

drug is inactive before metabolism e.g., codeine (latex of poppy flower)

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7
Q

define active drug

A

drug takes effect directly (three types when metabolised)

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8
Q

list the three types of metabolites of an active drug

A

Less active metabolite
More active metabolite
Inactivate metabolite

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9
Q

what is the common property of a compound after it has been metabolised

A

results mostly in the formation of more water-soluble compounds (hydrophilic) so it can be excreted through urine

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10
Q

what are the two phases of metabolism

A

phase 1: forms a derivative (functionalisation)

phase 2: conjugation = forms a further molecule making it more water soluble

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11
Q

do all drugs go through all phases

A

no and some don’t get metabolised at all

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12
Q

define phase 1 & example of reactions

A

= introducing a reactive (polar functional) group

  • catabolic
  1. oxidation
  2. reduction
  3. hydrolisis = more water soluble
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13
Q

what is the main enzyme that is responsible for the reactions in phase 1 of metabolism

A

CYP3A4/5

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14
Q

where are enzymes located

A
  • liver, ER
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15
Q

how do the drugs reach the enzymes

A

they must cross the plasma membrane

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16
Q

what is different about the large family of enzymes called cytochrome P459 enzymes

A
  • amino acid sequence
  • sensitivity to inhibitors & inducers
  • specificity of catalysed reaction
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17
Q

define phase 2

A

= conjugation (attach) drug with endogenous substance = transferase enzymes

  • anabolic
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18
Q

what does phase 2 usually result in

A

the production of inactive products

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19
Q

where does phase 2 commonly occur

A

the liver

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20
Q

define stereoisomers

A

two or more compounds differing only in spatial arrangement of their atoms

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21
Q

define stereoselectivity

A
  • even though the drug is the same their stereoisomer may diff in pharmacological effect & metabolism
  • one might be linked to toxicity
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22
Q

factors that affect metabolism

A
  • genetic factors
  • induction & inhibition cytochrome P450 enzymes
  • concentration-dependent biotransformation
  • disease-induced factors
23
Q

define an inducer

A

makes the enzyme work faster = more substrate becomes the product so less warfin for example (table)  could be bad more clotting (therapeutic failure)

24
Q

define an inhibitor

A

inhibit enzymes = inhibit enzyme = inhibit metabolise = increase substrate = toxicity: internal bleeding e.g., increase grapefruit juice consumption

25
Q

define excretion

A

= removal of a drug or metabolite from the body

26
Q

in what form are most drugs excreted

A

unchanged (20%) or as polar metabolites

27
Q

routes of drug excretion

A
  1. kidneys
  2. hepatobiliary system
  3. pulmonary
  4. sweat, saliva, tears
  5. breast milk
28
Q

what are the three important processes that can affect drug renal excretion

A
  1. Glomerular filtration = drugs cross glomerular filter freely, unless highly bound to plasma protein (then would go to efferent)
  2. Active tubular secretion = basic drugs in their pronated form are transported by organic cation transporters (OCTs) while acidic drugs are transported by organic anion transporters (OATs) (needs energy)
  3. Passive tubular reabsorption = lipid-soluble drugs are not efficiently excreted in the urine because they are passively reabsorbed along with water by diffusion across the tubular barrier
29
Q

example of alcohol metabolised

A

aka ethanol is metabolised into acetaldehyde & if lacking the enzyme to further metabolise build up of acetaldehyde = causes flushing of face

30
Q

what proteins are important to carry drugs in hepatobiliary x3

A

Organic cation transporters (OCTs)
organic anion transporters (OATs)
P-glycoproteins (P-gps)

31
Q

what happens in the hepatobiliary circulation (excretion) x3

A
  • drugs are transported from plasma to bile
  • After reaching the small intestine, drugs can be reabsorbed to be excreted by the kidneys or recirculate (hepatobiliary system) until completely excreted in the urine or faeces
  • Glucuronide conjugated drugs can be metabolised in the intestine & the free drug reabsorbed can be reactivated
32
Q

factors that can affect excretion - drug interactions

A
  • altering protein binding & hence filtration
  • inhibiting tubular secretion
  • altering urine flow
33
Q

define elimination half life

A

time taken for plasma concentration (Cp) to decrease by half

34
Q

how does the half-life assist in prescribing drugs x3

A 
o Duration of action after single dose. The longer the half-life, the longer the plasma concentration in the therapeutic range
oDosing frequency (how often have to take it)
oTime required to reach steady state (need of a loading dose)
35
Q

the usual time for drug elimination

A

6 half lifes

36
Q

half life in comparison to Vd & clearance

A

o T ½ is directly proportional to volume of distribution & inversely proportional to total clearance (CLtot)

37
Q

define clearance

A

o Clearance is the volume of plasma that is “cleared” completely of the drug per unit time (L/H

38
Q

what is the equation for clearance

A

rate of elimination divided by the plasma concentration

39
Q

how does the total clearance assist in prescribing drugs

A
  • determines maintenance does & rate of administration
40
Q

define steady state

A

rate of input to the body is equal to the rate of elimination

41
Q

at what time does steady state usually occur

A

after 3-5 half lives with repeated dosing or sustained release of drug

42
Q

equation for steady state x 2

A
  1. rate of drug administration divided by clearance

2. if the drug is taken orally then Fx dose divided by the total clearance x dosing interval

43
Q

equation for initial concentration

A

q (administered dose) divided by volume of distribution

44
Q

what does CL stand for

A

clearance

45
Q

define elimination rate constant

A

(kel) represents the fraction of drug in the body eliminated per unit time (1/time)

46
Q

equation for kel x2

A

0.693 divided t1/2

total clearance divided by volume distribution

47
Q

what does a kel of 0.4 s^-1 mean

A

that 40% of the drug is eliminated each second

48
Q

what are the two types of elimination kinetics

A
  1. first-order elimination kinetics

2. zero-order kinetics

49
Q

define first order kinetics of elimination

A

constant proportion of drug is eliminated per unit of time = concentration changes amount

= curve on the graph

50
Q

define zero-order kinetics (saturation)

A

= constant amount of drug is eliminated per unit of time

= independent of concentration

= negative linear line

51
Q

for a drug to be metabolised and excreted needs to be absorbed into which compartment

A

central compartment

52
Q

importance of pharmacokinetics x4

A

Drug development
Individualised dose regimens
Rational dose adjustment
Determining loading dose

53
Q

most drugs are secreted into the renal tubule via

A

active transport

phar24 (12 decks)

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