2: Drug movement in the body Flashcards
What are the four processes making up the fates of drugs in the body?
Absorption
Distribution
Metabolism
Excretion
What is absorption?
Process by which drugs enter the body from their site of administration
What is distribution?
Movement of drug from site of administration, through the bloodstream, and into the tissues
What is metabolism of a drug?
Conversion of active drug to a less active form by enzymes
Where does drug metabolism usually occur?
Liver
What is excretion of a drug?
Removal of drug from the body
Where does drug excretion usually occur?
Kidneys
In which two organs are ingested drugs absorbed?
Stomach
Small intestine
By which circulation do ingested drugs reach the liver?
Portal circulation
Where do drugs go once they have been metabolised in the liver?
Kidneys for excretion
usually
Drugs with (high / low) lipid solubility will be absorbed more quickly.
high
Drugs with (high / low) lipid solubility will be absorbed slowly.
low
Can ions move easily across the phospholipid bilayer?
No
An acid (donates / accepts) protons.
A base (donates / accepts) protons.
Acids are proton donators
Bases are proton acceptors
Only the (ionic / unionised) forms of drugs move easily across the phospholipid bilayer.
unionised
How is pH calculated?
pH = -log10[H+]
What is pKa?
Acid dissociation constant
i.e pH at which drug is 50/50 ionised/unionised
Acidic drugs become (more / less) ionised in an acidic environment.
How does this affect their lipid solubility?
less
Greater absorption due to increased lipid solubility (unionised)
Basic drugs become (more / less) ionised in a basic environment.
What effect does this have on their lipid solubility.
less
Greater absorption due to increased lipid solubility (unionised)
Where does the overwhelming majority of absorption occur?
Small intestine
What is motility?
Rate of stomach emptying and food movement through the intestines
Apart from drugs, what affects gastrointestinal motility?
Presence of food in the GI tract (see satiation signals)
In the presence of food, gastrointestinal blood flow (increases / decreases).
What cardiovascular condition can this cause?
increases
Angina
What is oral availability?
The amount of drug which reaches the systemic circulation after oral ingestion
or
amount in system circulation / amount ingested
What is systemic availability?
The fraction of drug which reaches the systemic circulation after absorption
or
amount in system circulation / amount absorbed
What is the systemic availability (%) of IV drugs?
100%
What is oral administration?
Ingestion by mouth
What is sublingual administration?
Drug held under the tongue
What is buccal administration?
Drug held against the inside cheek
What is rectal administration?
Drug inserted via the rectum
What is intravenous administration?
Drug administered via veins
What is intramuscular administration?
Drug injected directly into muscle
What is subcutaneous administration?
Drug administered under the skin
What is inhalational administration?
Drug is breathed in (e.g nebulised salbutamol)
What is transdermal administration?
Drug is applied to skin (e.g patches)
What is topical administration?
Drug is applied to specific skin surfaces / mucous membranes
Only (ionised / unionised) drugs move readily by diffusion.
unionised
because cell membranes are impermeable to ions.
What is volume of distribution (Vd)?
What is the unit?
Amount of drug in body / Plasma concentration
Litres (L)
