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PHARMACOLOGY FRCA > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

how does the dosing or oral and IV GTN differ?

A

oral much higher because high first pass metabolism

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2
Q

how does protein binding affect Vd?

A

depends if plasma or tissue proteins
plasma proteins - low Vd
tissue proteins - high Vd

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3
Q

can the Vd be larger than total body volume?

A

yes

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4
Q

what is the formula for Vd?

A

Concentration = mass of dose/Vd.

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5
Q

what are the 2 main plasma binding proteins?

A

albumin and alpha1-acid-glycoprotein

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6
Q

is desflurane a good induction inhalation agents?

A

no because smells and irritant to airways
(however it is fast)

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7
Q

how much is desflurane metbaolised?

A

0.2%

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8
Q

all inhalation agents except one are metabolised to trifluoroacetic acid. which one?

A

sevoflurane

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9
Q

what is more soluble in blood N20 or N2?

A

Nitrous oxide is more soluble than nitrogen in blood

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10
Q

what is MAC a measure of and what does it correlate to in terms of physical properties?

A

MAC is a measure of potency and correlates with lipid solubility (and therefore oil:gas partition coefficient).

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11
Q

what determines speed of onset of inhalation agents?

A

blood:gas coeffiecient - lower blood solubility the quickest

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12
Q

which is the most potent inhaled agent?

A

halothane

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13
Q

what does pregnancy do to speed on onset of inhalation anaesthetic?

A

increases
There are several physiological changes in pregnancy: hyperventilation and reduced FRC will favour a faster onset, but an increased cardiac output would tend to oppose this. Overall the respiratory effects predominantly increase the speed of onset

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14
Q

how does emphysema affect speed of onset of inhalation anaesthesia?

A

Emphysema increases the FRC volume and dilutes the agent in the alveoli.

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15
Q

how is thiopentone handled in phase 1 metabolism?

A

oxidation

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16
Q

what is the most common form of phase 1 reaction? what are the other types of reaction for phase 1

A

oxidation

reduction and hydrolysis are the others

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17
Q

list some enzymes involved in phase 1 reactions?

A

cyp450
monoamine oxidases
monooxygenases
esterases

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18
Q

high extraction ratio is dependant on what
low extraction ratio is dependant on what?

A

high - blood flow

low - protein binding

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19
Q

do the following have high or low extraction ratio? Propofol, ketamine, etomidate and morphine

A

all high

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20
Q

how does fat change in elderly?

A

increase in fat

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21
Q

how is half life related to time constant?

A

half life = 0.693 x time constant

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21
Q

how does urine pH change excretion of drugs

A

weak acids are excreted faster in alkaline urine as alkalinity promotes the dissociation of acid into ion and conjugate base

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22
Q

what is the equation for the graph showing concentration of a drug with time in first order kinetics?

A

C = C0e-k.t
negative exponential - decreases exponentially with time.

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23
Q

what is the equation relating clearance to elimination rate constant?

A

Clearance = Vol of distribution (Vd) x elimination rate constant (Ke).

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24
Q

what reactions make up phase 2 metabolism?

A

sulphation, glucuronidation, acetylation, methylation.

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25
Q

list some meds that are prodrugs?

A

codeine, diamorphine, enalapril

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26
Q

which of the following have active metabolites… morphine, diazepam, pethidine, atracurium and pancurium?

A

all of them

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27
Q

which metabolite of morphine is clinically active?

A

morphine - 6 -glucuronide

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28
Q

how is vancomycin elimated?

A

excreted by kidneys unchanged

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29
Q

where are cyp450 enzymes found?

A

hey are primarily found in the liver, bound to the lipid bilayer of the S endoplasmic reticulum of hepatocytes.

also found in the kidneys, and adrenals.

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30
Q

what are roles of CYP450

A

make drugs more hydrophilic for excretion - phase 1
synthesis of physiologically active substances

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31
Q

which CYP metabolises fentanyl and midazolam

A

CYP3A4 is involved in the metabolism of fentanyl

32
Q

how does t1/2 relate to T (half life and time constant)

A

t1/2=0.693T

33
Q

how does clearance relate to Vd?

A

clearance = Vd x k
(k = rate constant of elimination)

34
Q

how does Time constant relate to rate constant of elimination?

A

T= 1/k

35
Q

can kidney failure effect bioavailability?

A

yes as renal failure can have an effect on liver and GIT function

36
Q

what is the intercompartment clearance and elimination clearance equations?

A

Inter-compartmental clearance is given by V1.k12 or V2.k21.

elimination clearance is given by V1.k10

37
Q

what is the following equal too… ln2/k

A

half life
ONLY for first order kinetics, 1 C model

38
Q

how many exponential processes in a 1C , 2C and 3 C model?

A

1C = 1
2 C = 2
3C =3

39
Q

for propofol how does the intercompartment clearance compare to elimination clearance?

A

elimination clearance > inter compartment

40
Q

what is the different between a mamillary model and catenary model?

A

mamillary - V2 and V3 each connected to central compartment

caternary V1–> V2–>V3

41
Q

how does the intercompartment clearance of second compartment compare to third ?

how do these compare to elimination clearance?

A

The third compartment has a smaller inter-compartmental clearance than the second compartment

Inter-compartmental clearance between the central and second compartment may be greater than elimination clearance e.g. fentanyl and alfentanil (but usually elimination clearance is larger)

42
Q

which of the opioids has smallest Vd?

A

remifentanil

43
Q

the volume of the 3rd compartment directly reflects lipid solubility true or false

A

false related but not directly reflected by

44
Q

Why is fentanyl shorter acting than morphine

A

Very lipophilic.
Distributes via intercompartments

45
Q

how does concentration of a drug change with time in first order kinetics

A

negative expontential decay - the rate of decay changes with time

There is a constant proportionality between concentration and rate at which concentration falls: dC/dt = -kC.

46
Q

what has a greater intercompartmental clearance - fentanyl or propofol?

A

fentanyl

for fent intercompart> elimiantion clearance
for prop elimination clearance > intercompartment

47
Q

what is the equation for loading dose?

A

loading dose = Css x Vd

Css = plasma conc at steady state i.e. your target

48
Q
A
49
Q

A drug behaves according to a single-compartment model. Experimentally you find that it has a half-life of 70 min and a clearance of 100 ml/min. Which one of the following is its approximate volume of distribution?

A

equations:
T1/2 = 0.693 x T
T= 1/k
Clearance = Vd x k

therefore answer is 10L

50
Q

The clearance of a drug is 1.4 L/min. The initial half-life is 10 min. What loading dose is required to give a plasma concentration of 10 mcg/ml?

A

equations:
T1/2 = 0.693 x T
T= 1/k
Clearance = Vd x k
PLUS
loading dose = Css x Vd

answer = 200mg

51
Q

what info is needed when measuring clearance after an oral dose,

A

bioavailabilty fraction

52
Q

list factors that can alter pharmacokinetics of a drug ?

A

age, BMI, other drugs, hepatic or renal failure.

53
Q

how long before the context sensitive half life of propofol is constant

A

around 70 hours

54
Q

how long does it take a steady state fentanyl infusion to be reached?

A

60 hours

55
Q

when an infusion is stopped what does the duration of its hypnotic effect depends on?

A

how much was in the plasma at steady state
CSHT

56
Q

what reaches steady state quicker - propofol or remifentanil?

A

remi as it has a smaller Vd

57
Q

what is the elimination of clearance for propofol and fentanyl?

A

propofol - 1.9L/min
fentanyl 600ml/min

58
Q

how does absorption of drugs in neonates compare to adults?

A

slower due to longer gastric emptying time

59
Q

when can adult metabolism of drugs in a neonate be similar to adults?

A

some drugs after 2-4 weeks e.g. barbiturates

60
Q

what is GFR in neonates compared to adults?

A

20-40%

61
Q

how does aging change the GI absorption of drugs?

A

Ageing is associated with changes in gastric pH, slowing of gastric emptying, and reduced small bowel surface area

62
Q

how does body water change with age?

A

decreases with age

63
Q

how is bio-availability affected in elderly?

A

may be higher due to reduced hepatic flow and thus reduced extraction fraction

64
Q

what factors in pregnancy effect pharmacokinetics?

A

Hepatic blood flow
Hormone levels
Placental enzymes - some can metabolise drugs
Cardiac output
Protein binding

65
Q

how do opioids affect absorption of other drugs?

A

Opioid analgesics may lead to impaired absorption of enterally administered drugs - changes gastric motility

66
Q

how is the free fraction of drug altered in pregnancy?

A

increased
less PB

67
Q

how does body water compare in neonates?

A

higher percentage

68
Q

how does obesity affect lorazepam metabolism?

A

increased metabolism - decreased sedation effect

69
Q

how is pharmacokinetics affected in septic shock ?

A

decreased plasma proteins - increase in free fraction
reduced hepatic activity as making acute phase proteins
delayed feeding causes gut atrophy - reduced absorption
hepatic blood flow increases when hyperdynamic circulation and then reduces in shock

70
Q

what can the minto model be used for?

A

remi
also propofol

2 separate models by same company - allows use concurrently

71
Q

how does the central compartment vary in schnider?

A

it doesnt
central compartment is fixed

72
Q

which mathematical/ pharm model for propofol uses lean and actual body weight?

A

schnider - lean
marsh - actual

73
Q

what are the mathematical compartment models for TCI for fentanyl and alfentanil and ketamine?

A

fentanyl - shafer
alfentanil - maitre
ketamine - domino

74
Q

which 2 CYP 450 enzymes show most pharamacokinetic variation?

A

CYP2D6 & 2C9

75
Q

which CYP450 enzyme metabolises carvidilol and what can inhibit this?

A

CYP 2C9 -

amiodarone inhibits this

76
Q

what drugs are metabolised by CYP 2C9?

A

losartan
glipizide
warfarin
carvidilol
NSAIDS and selective COX 2 inhibitors
fluoxetine, phenytoin

77
Q

polycyclic hydrocarbons in cigarrete smoke induce CYP - which enzyme and which drugs does this effect?

A

1A2
2E1
caffeine, theophylline and propanolol

78
Q

What is the feature of a sprotte needle that reduces post Dural headache

A

Sprotte needle = spinal needle
Has a bevel to reduce trauma

PHARMACOLOGY FRCA (13 decks)

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