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Pharmacology > Pharmacokinetics 1 and absorption > Flashcards

Pharmacokinetics 1 and absorption Flashcards

1
Q

what are the 4 stages pharmacokinetics?

A
  • Absorption from the site of administration
  • Distribution within the body
  • Metabolism (breakdown and/or conjugation)
  • Excretion
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2
Q

Pharmacodynamics

A

what a drug does to the body

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3
Q

pharmacokinetics

A

what happens to the drug in the body

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4
Q

Pharmacodynamics specificity

A

Specific to drug or drug class

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5
Q

pharmacokinetics specificity

A

Non-specific, general processes

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6
Q

Pharmacodynamics specificity relies on

A

-Interaction with cellular components
-Effects at the site of action
Concentration-effect relationship
-Modification of disease progression
-Unwanted effects
-Drug interaction
-Inter- and intra-individual differences

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7
Q

pharmacokinetics in the body relies on

A
  • Absorption from the site of administration
  • Delivery to site of action
  • Elimination from the body
  • Time to onset of effect
  • Duration of effects
  • Drug interaction
  • Inter- and intra-individual differences
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8
Q

ethanol metabolism

A

draw it out

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9
Q

why is pharmacokinetics important?

A

Critical to new medicines research and development

Understanding pharmacokinetics is important to prescribing safely

Understanding what can go wrong with drug dosing and drug-interactions

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10
Q

what are Fentanyl Transdermal Patches?

A

opious drug which is 100 times more potent than morphine

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11
Q

what enzyme metabolises Fentanyl?

A

cytochrome P450 3A4 isozyme

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12
Q

what affects release and how much is released and onset?

A

12-18 hour onset to reach peak pain relief (slow onset so people think they need more)

temp affects release

40% still in the patch after 72hours

levels fall to 50% after removing the patch 17 hours prior

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13
Q

what are the major routes of administration of drugs into the body?

A 
Sub lingual 
IV
Oral 
Sub cutaneous
Up the bum – suppository – rectal
Inhalation
Nasal 
Intramuscular 
Intravitreal (in the eye) 
Trans dermal – patch on the skin
Pessary 
spinal canal - into csf
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14
Q

why is intramuscular quicker to get into the blood stream that intradermally?

A

there are larger and more blood vessels in the blood

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15
Q

Oral administration - Advantages

A
  • Easy
  • Slow release
  • drugs can be formulated to protect against digestive enzymes and acid
  • cheap and safe
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16
Q

Oral administration - Disadvantages

A
  • unsuitable for patients strictly mil by mouth
  • mostly absorbed slowly
  • unpredictable absorption
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17
Q

Rectal administration - Advantages

A

good absorption, avoids the first pass metabolism - haemorrhoids vein drains directly into the inferior vena cava

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18
Q

Inhalation administration - Advantages

A

large SA, bronchodilators steroids targeted to lungs with low levels of absorption

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19
Q

Inhalation administration - Disadvantages

A

bioavailability depends on the patients inhaler technique and the size of the particles generated

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20
Q

Where are most drugs that are taken orally absorbed?

A

in the small intestine - large SA

some absorption can take place in the stomach

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21
Q

which factors affect absorption?

A 
ionisation of a drug
molecular size
gut content (fasted/fed)
GI motility
particle size and formulation
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22
Q

at what molecular weight does passive absorption become worse/

A

> 500nm

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23
Q

how long does it take 75% of drugs to be absorbed after being taken orally?

A

1-3 hours

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24
Q

how are drugs that are taken orally absorbed?

A

Passive difusion, carria media transporters, pinocytosis/endocytosis

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25
Q

all drugs have to bass at least one cell barrier in order to get into the effector tissue - one method excluded - which is this?

A

Intra venous

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26
Q

which kind of cell linings are often present barriers to drugs moving from one ‘compartment’ to another

A

epithelial and endothelial

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27
Q

which barriers are the most difficult to permeate/

A

BBB and placental

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28
Q

what do aqueous pores do

A

allow transport of materials

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29
Q

where would you mind fenestrated capillaries

A

GI tract, renal glomeruli, endocrine glands, choroid plexus

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30
Q

which organs would you fined pores in the capilaries

A

liver, spleen and bone marrow

drugs freely pass and so detox and excrete

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31
Q

where would you find tight junctions in capillaries?

A

BBB, muscle and heart

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32
Q

what ways can drugs cross membranes?

A

Passive diffusion, though aq pore, and carrier protein (requires ATP), pinocytosis take up into vesicle (requires ATP)

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33
Q

what will diffuse across across a lipid membrane?

A

only unionised (non charged form of the drug)

34
Q

what do drugs ionise according to?

A

their pKa

35
Q

Weak acids will be ionised at

A

higher pH

36
Q

Weak bases will be ionised at

A

lower pH

37
Q

The pKa is the pH at which ionised and non-ionised forms are..

A

equilibrium

38
Q

Alkali drugs

A

high pKA – ionised in acidic condions

39
Q

why does aspirin get trapped in the urine?

A

has a low pKa due to being a weak acid- the urine has a high pKa

40
Q

why is neurotoxin safe to eat in meat?

A

neurotoxin is basic - so has a high pKa the gut has a low pKa so safe to eat

41
Q

alkalising urine can be used to treat overdoses of what drugs

A

weak acids

42
Q

where are strong bases ionised?

A

in the intestines

- poor absorption

43
Q

with a weak acidic drug such as aspirin where will it be most ionised? pH?

A

in alkaline pH - such as in the urine

44
Q

what is the pKa of aspirin?

A

3.5

45
Q

pethidine is a weak base drug with a pKa of 8.6, where will ionisation the base be greatest?

A

low pH, such as in the stomach

46
Q

carriers in cell membranes mediate the transport of what?

A

sugars, amino acids, neurotransmitters and metal ions

47
Q

what do solute carrier transporters (SCLs) do?

A

passively transport substrates down its concentration gradient

48
Q

active transport -

A

transferring against the concentration gradient - requires ATP

49
Q

how many genes are thought to code for transporters

A

300

50
Q

to traverse cellular barriers (Mucose, BB, placenta) drugs must cross

A

lipid membranes

51
Q

drugs cross lipid membranes by

A

passive diffusion transfer or carrier - mediated transfer

52
Q

what is the main factor that determines rate of diffusional transfer across membranes?

A

drugs lipid solubility

53
Q

what is a less important factor in determining rate of diffusional transfer?

A

molecular weight

54
Q

henderson- hasselbalch equation states

A

ionisation of weak acids and weak bases varies with pH

55
Q

with weak acids and weak bases only……. can diffuse across lipid membranes - pH partition

A

uncharged species

  • protonated form of weak acid
  • unprotonated form of weak base
56
Q

what does pH partition mean?

A

that weak acids tend to accumulate in compartments of relatively high pH (weak bases do the reverse)

57
Q

carried mediated transport in the renal tube,BB and GI epithelium is important for some drugs that are

A

chemically related to endogenous species

58
Q

Bioavailability (F)

A

extend and rate at which the active moiety of the drug or metabolite enters the circulation, thereby accessing the site of action.

59
Q

what bioavailability does IV immediately give?

A

100%

60
Q

how would you work out bioavailability?

A

blood plasma conc. curve

Area under the curve oral route / area under the curve IV

= absolute bioavailability

61
Q

insulin bioavailability

A

0% - broken down by enzymes

62
Q

what is the first pass effect?

A

where when a drug is taken - absorbed into the GI tract - passes through the portal vein into the liver - the liver breaks down and greatly reduces the bioavailability of the drug

63
Q

which would have a longer half life? IV or oral?

A

Oral

oral would take longer to onset, have a more blunter peak plasma concentration and longer duration of action

64
Q

what affect does slower absorption of drug have on peak conc.

A

lower peak

65
Q

Intra venous administration allows

A

rapid onset and full absorption of drug

66
Q

what is an IV loading dose called?

A

bolus

67
Q

what 2 methods of IV are combined to maintain blood concentration?

A

iv bolus (loading dose) and then Iv infusion

68
Q

IV infusion avoids

A

first pass

69
Q

sublingual absorption

A

under the tongue - mucous membrane with lots of capillaries, straight into the blood so avoids first pass

70
Q

would rectal or oral have higher bioavailability?

A

rectal

71
Q

Nasal sprays

A

nasal cavity is well vascularised, quick into circulation, small molecules with a local effect

72
Q

intravitreal uses

A

-used for diabetes retanopothy

73
Q

(eye drops)

A

saline based

- antihistamines or antibiotics

74
Q

what is intrathecal

A

straight into the spinal canal - into the CSF - crosses the BBB

75
Q

what are prodrugs?

A

drugs which are administered but the need to be metabolised by the body to become the active form

76
Q

example of prodrug?

A

codine - created into morphine

AZT - doesn’t have direct effect on HIZ, effects reverse transcriptase

77
Q

which enzyme converts coding to morphine

A

CYP2D6

78
Q

the specialist formulation of the contraceptive implant - how does it work?

A

releases hormones slowly, made of copper which also has a natural effect on our hormone levels

79
Q

how are antibody-drug conjugates used?

A

mainly used against cancer, drug which has a selective antibody and a cytotoxic agent - antibody sticks to marker on cancer cell and binding causes the reaction to kill the cells

80
Q

which form of dosing is most common?

A

oral

81
Q

most absorption of oral is in

A

the small intestine

82
Q

bioavailibilty requires

A

absorption and surviving early metabolism (GI wall and first pass)

Pharmacology (18 decks)

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