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PHARM 203 > Topic 7 - Drug Absorption and Distribution > Flashcards

Topic 7 - Drug Absorption and Distribution Flashcards

1
Q

ADME

A

Absorption
Distribution
Metabolism
Excretion

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2
Q

Absorption

A

Movement of drug from where it was administered into the bloodstream

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3
Q

Enteral

A

Administration that passes through the intestines
Passes through liver

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4
Q

What routes are Enteral

A

Oral (PO), Rectal (PR)

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5
Q

Parenteral

A

Route that bypasses the intestine
Avoids the liver

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6
Q

Parenteral Routes

A

Intravenous (IV)
Intramuscular (IM) Subcutaneous (SC)
Topical
Sublingual (SL)

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7
Q

What routes bypass the liver

A

Parenteral

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8
Q

Rectal Route (Overdose)

A

If drug is not pushed in deep enough then drug is absorbed by rectal walls –> Drug goes directly into blood vessels while avoiding the liver

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9
Q

How does polar impact lipid solubility

A

The more polar a drug is the less likely it can cross the lipid bilayer

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10
Q

The more N and O molecules in a drug the more?

A

The more polar it is meaning the less lipid soluble it is

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11
Q

Higher logP means?

A

The drug is very hydrophobic

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12
Q

Low Polar Surface Area means?

A

The drug is more lipid soluble

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13
Q

Fick’s Law of Diffusion

A

Drugs flow from high concentration to low concentration

The larger the gradient the higher the rate of flow

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14
Q

Why is Lipid Solubility important in crossing the membrane?

A

A very lipid soluble drug will partition into the bilayer quite easily

Forms a larger gradient within the bilayer which drives the rate of flow

There is way more drugs to move within the bilayer

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15
Q

Ionization effects on Absorption

A

Charged drugs do not diffuse across membranes as they are water soluble

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16
Q

Ionization effects on Absorption (pH and pKa)

A

An acid in an acidic environment will be less ionized and will favour more of the lipid soluble form

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17
Q

Route that a drug takes when taken orally

A

Stomach –> Intestine –> Portal Vein –> Liver –> Systemic Circulation

18
Q

First Pass Metabolism

A

Drugs taken orally have to pass through the Liver before they enter the systemic circulation

19
Q

On average how many times will a drug past the liver

A

About once every four circuits will the drug pass through the portal vein and the liver again

20
Q

What is oral bioavailability

A

The intact drug, a fraction of an oral dose that reaches the systemic circulation

21
Q

Fraction Escaping Gut (Fg)

A

Amount of drug that enters the portal vein and leaves the intestines

drug in portal vein / drug dose

22
Q

Fraction Escaping Liver (fH)

A

Amount of drug that is left over after being metabolized by liver

drug in systemic circulation / drug in portal vein

23
Q

Hepatic Extraction Ratio (EH)

A

1-fH
1 - drug in systemic circulation
Amount of drug that is removed by liver

24
Q

Oral Bioavailability (F)

A

fg x fh
Fraction of drug that escaped the intestines x Fraction of drug that escaped the liver

or

Amount of drug escaping liver / dose of drug taken

25
Q

Thoracic Duct

A

Chylomicron carries lipophilic drugs through the thoracic duct to enter the systemic circulation

26
Q

Apparent Volume of Distribution

AVd

A

A theoretical volume of plasma that contains all of the drug in the plasma

Creates a concentration equal to the plasmas

27
Q

Calculating AVd

A

1) Check concentration of drug in plasma (10mg/L)
2) Check original dose given (100mg)
3) Determine volume of distribution
100mg/X = 10mg/L
X = 10L

28
Q

Why do we use AVd instead of concentration of drug in systemic circulation

A

Amount of dose impacts the systemic circulation concentration, meaning it is not consistent

A change in dose will change concentration and thus, changes AVd, makes it a better value for comparison

29
Q

Systemic Circulation and Distribution Relationship

A

High distribution means there is less concentration of drug in systemic circulation

30
Q

What determines AVd (Tissue Factors)

A

Lipophilic unbound drugs will be partitioned in fat and will not be free for binding

31
Q

What determines AVd (Blood Factors)

A

Plasma Protein Binding, Drugs bound to plasma proteins are unavailable for binding

32
Q

AVd Formula

A

Plasma Volume + Volume of Tissue x (fu/fuT)

fu = fraction of unbound drug in blood
fuT = fraction of unbound drug in tissue

33
Q

What happens where their is less plasma proteins

A

More unbound drug

34
Q

fu/fuT ratio greater than 1 means that?

A

Low Tissue Unbound, lots of drugs bound and partitioned in fat
Very Lipophilic

Fraction of unbound drugs in blood is greater than the fraction of unbound drugs in tissue

35
Q

fu/fuT ratio less than 1 means that?

A

Low plasma drug unbound –> Lots of drug is bound to plasma –> Drug is hydrophilic

36
Q

Lipophilicity and Drugs Bound

A

Low amount of unbound drugs in plasma = Hydrophilic drug (Drugs are all bound to plasma proteins)

Low amount of unbound drugs in tissue = Lipophilic drug (Drugs are all bound to fat)

37
Q

Competition for Plasma Binding Proteins

A

A competing drug can bind to plasma proteins and displace the initial drug

Leads to an increase in drugs in plasma = increase of drug in tissue = Larger response

38
Q

Distribution Compartments

A

A model that helps us to understand drug behaviour and distribution

Not physically real

39
Q

Central Compartment

A

Blood and other highly vascularized tissues (Brain) that distribute any incoming drug instantly

Drugs leave via Liver etc.

Is in equilibrium with tissue compartmentes

40
Q

Shallow Tissue Compartment

A

Tissues and organs that rapidly distribute a given drug

41
Q

Deep Tissue Compartment

A

Tissue and Organs that slowly distribute a given drug (Fat)

PHARM 203 (19 decks)

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