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Medicine Unit 3 > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

what type of drug is flucloxacillin

A

beta-lactam antibiotic

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2
Q

chemistry of flucloxacillin

A

has a fluoride and a chloride
has a core penicillin part
is a beta-lactam antibiotic so has a beta-lactam part in the structure

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3
Q

pharmacology of flucloxacillin

A

targets bacterial transpeptidase enzymes
=penicillin-binding protein (PBP)
activity: irreversible inhibitor
=suicide substrate

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4
Q

physiology of flucloxacillin

A

-D-ala-D-ala is integral part of cell wall peptidoglycan, PG: structure/synthesis
transpeptiases normally crosslink :the D ala to other amino acids in PG
beta lactase inhibition of the cell wall synthesis
dividing bacteria lose rigid cell wall integrity
osmosis and cells then pop
they’re bactericidal

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5
Q

clinical side of flucloxacillin

A

antibiotic
narrow spectrum, gram positive
infections caused by sensitive organisms e.g. staphylococcus and streptococcus

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6
Q

what is pharmacokinetics

A

what the body does to the drug
absorption, distribution, metabolism, excretion/elimination

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7
Q

what is pharmacodynamics

A

what the drug does to the body

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8
Q

absorption

A

from outside to inside
-routes of administration
-bioavailability
-drug properties
-biological properties

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9
Q

distribution

A

form one place to another in the body
-volume of distribution
-blood flow
-drug properties
-biological properties

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10
Q

metabolism

A

from one thing to another
-biotransformation
-transforming enzymes
-drug properties
-biological properties

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11
Q

excretion/elimination

A

from inside to outside
-clearance
-removal mechanisms
-drug properties
-biological properties

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12
Q

routes of administration

A

parenteral
enteral

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13
Q

parenteral definition

A

avoiding the gastro-intestinal tract

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14
Q

methods of parenteral administration

A

intravenous
intramuscular
sub-cutaneous
epidural
trans-dermal
sublingual
inhalation

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15
Q

intravenous

A

directly into the blood

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16
Q

intramuscular

A

directly into a muscle
highly vascular tissue

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17
Q

sub-cutaneous

A

under the skin
poorly vascular space q

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18
Q

epidural

A

into the epidural space

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19
Q

systemic

A

drug will be administered everywhere

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20
Q

topical

A

treatment is localised
e.g. local anaesthetic

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21
Q

trans-dermal

A

across the skin

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22
Q

sublingual

A

under the tongue

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23
Q

inhalation

A

through breathing via the lungs

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24
Q

enteral

A

via the gastro-intestinal tract

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25
Q

examples of enteral

A

oral
rectum

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26
Q

oral

A

into the mouth
then stomach
then intestines

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27
Q

rectum

A

e.g. suppositories

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28
Q

oral bioavailability

A

is the same as fractional availability
fraction of a drug that gets into the systemic circulation
100%= all the drug in the tablet gets into the plasma
higher the bioavailability the more useful the drug will be as an oral, systemic medicine

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29
Q

what factors affect oral bioavailability

A

drug stability within the gut
drug absorption across the gut wall into the blood
drug metabolism in the liver (first pass effect)

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30
Q

drug stability in the gut

A

chemical stability: acidic in the stomach, pH varies in small intestine
biological stability: enzyme action in the gut, intestinal bacteria
drug properties: chemical (the drug), pharmaceutical (the formulation), biological (the patient)

31
Q

drug absorption across the gut wall

A

gut is adapted
pathway: gut lumen, gut epithelium, extracellular matrix, capillary endothelium, blood vessel lumen

32
Q

what does absorption in the gut depend on

A

drug properties: solubility size, pKa
pharmaceutical
gut properties: anatomy, physiology, pathology

33
Q

which drugs cross membranes most easily

A

unionised

34
Q

weak acid and absorption

A

H+ + A- reverse HA
un-ionised form HA predominates
better absorption

35
Q

when does equilibrium shift

A

at low pH

36
Q

weak base and absorption

A

H+ + B reverse HB+
ionised form HB+ predominates
poor absorption

37
Q

drug metabolism in the liver

A

drugs with substantial hepatic metabolism may have poor oral bioavailability

38
Q

which is the principle organ of drug metabolism

A

the liver

39
Q

first pass effect

A

drugs absorbed in most of the gut pass entirely to the liver
hepatic portal vein runs from the gut to the liver

40
Q

how to calculate volume in ml

A

amount in mg/ concentration in mg.ml-1

41
Q

volume of distribution equation

A

total amount of drug in the body/ concentration in the plasma
defines the relationship between two real important values

42
Q

why concentration in the plasma

A

something measurable
directly related to clinical effects

43
Q

why is it an “apparent” volume of distribution

A

drug may not leave the blood, erythropoietin= very high Cp
drug freely enters/leaves the cells, cimetidine= low Cp
drug doesn’t enter the cells (evenly in the extracellular fluid)gentamicin= high Cp
drug accumulates in fat (lipophilic), midazolam=very low Cp

44
Q

effect of high blood flow

A

high blood flow to the brain
propofol= IV general anaesthetic
intravenous= rapid delivery to brain

45
Q

effect of low blood flow

A

low blood flow to the bones/cartilage/joints
antibiotics
difficult to achieve adequate concentrations of drug= infections difficult to treat

46
Q

what does the volume of distribution tell us

A

the distribution of the drug in the body compared to the plasma
how much drug is required in the body to achieve a specific concentration in the plasma

47
Q

what does metabolism do to drugs

A

alters the chemical structure
biochemical (enzymes)

48
Q

where are drugs metabolised

A

liver
gut wall
kidney
lung
plasma

any tissue with metabolic activity

49
Q

what are the two phases of drug metabolism q

A

synthetic
conjugation

50
Q

synthetic

A

oxidation: hydroxylation, dealkylation,deamination
reduction
hydrolysis
makes the drug more polar and soluble

51
Q

conjugation

A

glucuronidation
methylation
sulphation
acetylation
glutathione
makes drug larger
makes the drug more polar

52
Q

what do drugs change into in the synthetic phase

A

can convert to active, inactive, toxic metabolites

53
Q

what do drugs change into in the conjugation phase

A

converts drug to inactive form
except morphine

54
Q

phase one of phenacetin metabolism

A

it is a prodrug
and is inactive
changes to paracetamol
which is active

55
Q

phase one paracetamol metabolism

A

NAPQI
toxic and in phase two of this drug metabolism forms glutathione-conjugated paracetamol which is inactive

56
Q

phase two of paracetamol metabolism

A

forms glucuronide-conjugated paracetamol
inactive

57
Q

elimination

A

disappearance of the drug from the plasma
excretion: parent drug is physically gone
metabolism: parent drug changed into something else

58
Q

excretion

A

physical removal of the drug from the body
kidney-urine
lungs-breath
skin-sweat

59
Q

what is renal elimination promoted by

A

increased polarity
increased aqueous solubility
increased size
metabolites by phase one and two are normally faster eliminated

60
Q

rate of elimination

A

drug mg is eliminated from the plasma over time in mins
units: mg.min-1

61
Q

clearance

A

plasma ml is cleared of drug over time min
units: ml.min-1

62
Q

rate of constant elimination ke

A

proportion of drug (unitless) eliminated in one unit of time min
units: min-1

63
Q

half-life (t1/2)

A

time in min taken for the plasma concentration to fall by half
units: min

64
Q

what is the rate of elimination proportional to

A

the concentration

65
Q

what is the proportionality constant

A

clearance

66
Q

how to achieve a desired plasma concentration

A

dose= Vd x Cp
mg= ml x mg.ml-1

67
Q

how to maintain a desired plasma concentration

A

dose rate = Cl x Cp
mg.min-1 = ml.min-1 x mg.ml-1
cl= flow rate of leak

68
Q

how to calculate the half life

A

t1/2 =ln2 / ke
ke= rate constant of elimination

69
Q

if you increase the clearance what happens to the half-life

A

shortens

70
Q

for an oral drug what is ideal dosing q

A

once per da

71
Q

short half life q

A

second/minutes
onset/offset rapid
uses a lot of drug

72
Q

long half life

A

hours/days
onset/offset slow
uses less drug

73
Q

1st order elimination

A

constant clearance
rate of elimination is proportional to the concentration in the plasma
linear kinetics
practical, predictable and analytically simple

Medicine Unit 3 (28 decks)

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