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F1:CEP20/21 > Pharma absorption and distribution of drugs > Flashcards

Pharma absorption and distribution of drugs Flashcards

1
Q

What is pharmacokinetics?

A

describes how drugs move through the body

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2
Q

Describe the general trend of a plasma drug concentration time graph

A

at the start there is an increase in the plasma concentration as the drug is absorbed
absorption then begins to slow
the concentration of the drug then decreases over a longer period of time due to metabolism and excretion

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3
Q

what is the therapeutic index?

A

is the difference between the effective and toxic concentration of a drug

drugs with larger therapeutic indexes tend to be safer

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4
Q

What does ADME stand for?

A

Absorption
Distribution
Metabolism
Excretion

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5
Q

What is absorption?

A

the movement of a drug from the site of administration to the plasma

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6
Q

what is distribution?

A

how the drug gets to its target tissue

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7
Q

What is Metabolism and Excretion

A

the breakdown and then removal of a drug from its site of action

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8
Q

List the 4 factors that effect drug absorption

A

Route of administration

Blood flow surrounding and at site of administration
Good blood flow maintains a steep diffusion gradient

Dose
the larger the dose the larger the concentration gradient

drug solubility
lipophobic drugs readability dissolve in blood plasma
lipophilic drugs need transport being proteins in the blood

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9
Q

What are the three types of drug administration?

A

Enteral
Percutaneous
Parental

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10
Q

How does blood flow affect distribution?

A

Some organs have very high perfusion therefore will see the drug first e.g. brain liver, heart
some have very low perfusion e.g. adipose tissue

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11
Q

What is the main plasma binding protein for lipophilic drugs?
what does this mean?

A

Albumin

means an equilibrium exists at the site of action between the bound drug and albumin complex and the drug itself

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12
Q

How can diffusion barriers effect distribution?

A

Blood brain barrier and placenta highly controlled areas drugs may not be able to enter

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13
Q

What is tissue binding?

A

the preference of drug for a particular tissues receptors effects its distribution

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14
Q

What is ion trapping?

how does it affect distrobution?

A

Drugs are usually weak acids therefore have a equilibrium between an ionised and unionised form
only the ionised form can cross the CSM
yet drugs collect where ionisation is favoured

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15
Q

Where do weak acids collect and are absorbed best? Why does this happen?

A

In low pH’s equilibrium shifts to the right favouring the unionised HA form. As such weak acidic drugs diffuse and are distributed best in acidic environments
In basic environments (high pH’s) dissociation is favoured therefore drugs collect here e.g. urine

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16
Q

Where do weak bases collect and where are they absorbed best? Why?

A

In high pH’s (basic environments) the equilibrium shifts to favour the unionised form therefore they readily diffuse and are absorbed in these environments.
they accumulate in acidic environments e.g. the stomach as the equilibrium is shifted to favour dissociation

17
Q

What is fat trapping? Why is this significant?

A

lipid soluble drugs collect in fat this absorption is slow as there is a low blood supply to adipose tissue
as such the elimination form these environments is also slow and the drug may be release slowly form these areas long after the plasma concentrations have dropped.
Accounts for biphase elimination
this can be an issue if you are dosing overweight patients

18
Q

Where does first pass metabolism mainly occur?

A

The liver

metabolism also occurs in the kindly lungs and Gi tract

19
Q

What is phase 1 metabolism

NB Phase 1 and Phase 2 metabolism occur at the same time

A

Oxidation of drugs using CYP450 enzymes that introduce hydroxyl groups and make drugs more soluble therefore easier to excrete

20
Q

What is phase 2 metabolism?

A

conjugation of charged groups via cytoplasmic sulfotransferases –> this makes the drug even more hydrophilic and therefore makes it easier to excrete

21
Q

What are the consequences of first pass metabolism?

Why does this vary?

A

usually deactivated drugs
can also activate some prodrugs
people have different concentrations and variations of enzymes present hence the growing need for personalised medicine

22
Q

Give an example of a drug that is activated during first pass metabolism.

A

Tamoxifen is converted to 4 hydroxytamoxifen via CYP2D6 enzyme, used in breast cancer treatment

23
Q

What is the main organ involved in drug excretion

A

kidney

24
Q

How is the liver and other organs involved in Drug excretion?

A

Liver secretes metabolised drugs into bile –> can be an issue if then reabsored in the Gi tract as drug remains in a enterohepatic circulation loop

Lungs can expel gasses from metabolism of drugs and drug vapours in air

Saliva sweat and milk are other forms of secretion

25
Q

What is elimination?

A

Elimination = Metabolism+ excretion

26
Q

In the one component model what is the fate of the drug

A

first order elimination concentration halves every min for example (gets progressively smaller and smaller)

27
Q

What is zero order elimination

A

constant decrease in drug concentration

Why because elimination is not dependant on concentration of the drug but instead on the enzymes present

28
Q

What is biphase elimination

A

two component model there is an unequal elimination of the drug
this may be due to fat trapping

29
Q

What is the fate of an orally swallowed drug from administration to site of action? include steps where it can leave.

A

total oral does
(some may not be dissolved)

dissolved in Gi tract
(some may be broken down by stomach acid some is not absorbed. some may also be secreted int bile)

absorbed

In liver 
(metabolised first pass metabolism)

enters general circulation
(may be bound to plasma proteins this will be an equilibrium)

Enters tisses
(from blood or from dissociation from plasma protein)
may be metabolised or secreted and may be trapped (fat trapping)

at the site of action

30
Q

What is bioavailability?

A

the fraction of the total does administered that reaches the plasma this varies from individual to individual and depends on the route of administration

31
Q

What is AVD

Give the equation to figure out AVD

A

Apparent volume of distribution = volume of fluid required to dilute an absorbed dose to the concentration found in plasma

32
Q

What are the two eternal routes of administration.

give an advantage and disadvantage of each method

A

oral
A=convenient and cheap
D=must be able to withstand acidic conditions of the stomach as well as first pass metabolism

rectal
A=bypasses the liver
D= absorption often unpredictable and erratic

33
Q

What the three major parenteral methods of administration?

A

Intravenous
A= rapid response total dose absorbed
D= need a suitable vein and has to be sterile

Subcutaneous
A= slow but general complete absorption
D= painful and can cause tissue damage

Intramuscular

34
Q

What are the 3 major percutaneous methods of administration?

A

Inhalation
A=local systemic effect and bypasses liver
D= low doses only

Topical transdermal
varies on thickness of skin as to how much is actually absorbed

Sublingual
(placed under tongue and allowed to dissolve)

35
Q

What are the 5 major factors effecting transdermal absorption?

A

lipid solubility

formulation

skin thickness area, age and damage

hydration of the skin

blood flow

36
Q

Why are some orally administered drugs enteric coated?

an example fo pharma formulation

A

allows acid unstable drugs to and irritant drugs from breaking down in the stomach
breakdown in small intestine instead

37
Q

how does particle size affect absorption?

A

the smaller the particle the faster it is absorbed

38
Q

What is the plasma half life of a drug?

A

Time taken for half the does given to be eliminated from the plasma

F1:CEP20/21 (12 decks)

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