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ICPP 2023 > Pharmokinetics 2 > Flashcards

Pharmokinetics 2 Flashcards

1
Q

How is SA maximised in SI?

A

Plicae circularis
Villi
Microvilli

(30-35m2)

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2
Q

What is bioavailibility?

A

Fraction of defined dose which reaches specific body compartment
(circulation cost common ref compartment)

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3
Q

What is IV reference value bioavailabilty CVS?

A

100% - all reaches CVS

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4
Q

How are other routes of bioavailability compared?

A

Reference intravenous bioavailability (eg oral/IV)

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5
Q

Factors affecting drug absorption

A

Physiochemical
GI Physiology
First pass metabolism - GI and Liver

determine proportion of drug entering systemic circulation

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6
Q

How do measure bioavailability?

A

Plot plasma conc against time post dose
Calculate area under curve

for oral - area under oral curve/area under IV curve

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7
Q

Oral availability equation

A

F = amount reaching systemic/drug given IV

AUC

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8
Q

Where does F (bioavailability) lie?

A

Between 0 and 1

1 = all to systemic
0 = none to systemic
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9
Q

Drug distribution

A

How drugs travel through the body

  • therapeutic/non therapeutic (side effects) interactions
  • Interactions with other molecules
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10
Q

First stage - 3 parts distribution

A

Bulk flow: large distance via arteries –> capillaries

Diffusion: capillaries –> interstitial fluid –> cell membrane targets

Barriers to diffusion: Interactions/permeability/non target binding

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11
Q

Diffusion across capillaries affected by

A

Level of permeability

Expression of endogenous transporter/OAT, OCT

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12
Q

3 types capillaries

A

Continuous (closed, tight gap junctions, tight intercellular cleft)

Fenestrated (less tight cleft. fenestrations)

Sinusoid (leaky sinuses. big fenestrations)

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13
Q

Continuous found

A 
BBB
CNS
Muscle
Skin
Fat
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14
Q

Fenestrated found

A

Intestinal
Endocrine/exocrine glands
Kidney glomeruli

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15
Q

Sinusoidal found

A

Bone marrow
Lymph
Liver
Spleen

(allow cells out)

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16
Q

Large effect on pharmacokinetics is…

A

Heterogenous structures/tissues of body

Different body types

17
Q

Major factors affecting drug distribution

A

Lipophilicity/Hydrophilicity

Degree of drug binding to plasma/tissue proteins

18
Q

Lipophilicity/Hydrophilicity

A

If lipophilic - easily move across membrane

if hydrophilic - barriers are related to absorption barriers (capillary permeabilty, drug pKa, pH, OAT/OCT density)

19
Q

Degree of drug binding to plasma/tissue proteins

A

Drugs bind to proteins in circulation

eg. Albumin (globulin)
Lipoproteins (acid glycoproteins)

20
Q

Example albumin

A

If drug bound to albumin acts as ‘dynamic reservoir’ of drug
ONLY FREE DRUG can bind to targets
If drug binds to protein = decreased free drug available

21
Q

Binding to albumin

A

Binding not strong (equilibrium)

Multiple drugs can bind - competition for binding sites (affects pharmacokinetics)

22
Q

3 body fluid compartments

A 
Plasma water (3L)
Extracellular water (plasma (3) + interstitial (11) 14L)
Total body water (extracellular + intracellular 42L)
23
Q

Barriers at compartments

A

Capillary membrane barriers (between plasma and interstitial)

Target tissue membrane barriers (between interstitial and intracellular)

24
Q

What does increasing penetration of drug do?

A

Drug moves more readily from plasma –> interstitial –> intracellular

= decreased plasma drug concentration 
Increased Vd (volume distribution)
25
Q

Where are most drug targets located?

A

Membrane of intracellular cells

Only need to penetrate to interstitial to have effect

26
Q

Why is volume distribution (Vd) apparent?

A

Group all main fluid compartments as ONE compartment
= summary of drug through plasma, interstitial and intracellular

Pretend concept

27
Q

What is Vd usually referenced to?

A

Plasma concentration

dependent on push/pull factors

28
Q

What do values of Vd mean?

A

small Vd: less penetration of interstitial/intracellular compartment

large Vd: greater penetration of interstitial/intracellular compartment

29
Q

Vd units

A

litres (70kg standard assumed)

Litres/kg (affected by weight)

30
Q

Vd equation

A

Drug dose/plasma drug (at time =0)

31
Q

What can Vd be affected by?

A 
Blood flow
Hypoalbuminemia 
Body weight changes (increased lipid, more to pass through)
Other drugs
Renal failure - drug excreted slower
Pregnancy
Paeds
Geriatrics
Cancer

ICPP 2023 (31 decks)

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