Pharmacokinetics Flashcards
How is the route of drug administration divided?
systemic - entire organ is exposed to the drug
local - restricted to one area of the organism
How else can the route of administration be divided?
enteral - by the GI tract
parenteral - everywhere but the GI tract
Advantage and disadvantage of IV drug administration
- rapid onset
- invasive and requires training
Advantage and disadvantage of intraperitoneal drug administration
- rich blood supply so good absorption of the drug
- not a very common route and highly invasive
List all the routes of drug administration in the body
- dermal
- intramuscular
- subcutaneous
- intraperitoneal
- intravenous
- ingestion
- inhalation
Advantage and disadvantage of dermal administration
- extended release, limit the need to keep on topping up throughout the day
- tackle malabsorption issues
- strong dose cannot be administered in this way
advantage and disadvantage of inhalation
- drug localised to the target organ so as a result less adverse side effects occur
- lot of drug loss through the use of aerosol
advantage and disadvantage of oral drug
- easy for patients
- slow release
- non-invasive
- inefficient if there is malabsorption
What two ways do drugs move around the body by?
- bulk flow transfer
- diffusion transfer
Describe how the drug enters the blood stream through absorption?
The drugs travels to the GI tract where it is absorbed
-it travels to the liver via the hepatic portal system and then enters the systemic circulation
How can drugs cross both their aqueous and lipid environments?
- diffuse through the lipids
- diffuse through an aqueous pore in the lipid
- carrier molecules
- pinocytosis
How do most drugs exist?
ionised/ non-ionised
-most are either weak acids or bases
Explain what happens to aspirin as it moves from the stomach to the small intestines?
- Aspirin is a weak acid
- when it is in the stomach, that has a pH lower than itself it is encouraged to be non-ionised
- it exists the stomach in this form (meaning it can easily cross the lipiud bilayer)
- when it enters the small intestine, the pH becomes higher and so it becomes ionised
- it is harder for it to cross the lipid membrane in its ionized form- hence more absorption in the stomach compared to the intestine
What is ion trapping?
when part of the ionised drug ends up in the bloodstream but cannot move into tissues because it is in its ionised form - essentially trapping it in the circulation
List 4 factors influencing drug distribution
- regional blood flow
- extracellular binding
- capillary permeability
- localisation in tissues
How does extracellular binding effect distribution?
if a plasma protein is bound then the drug is no longer available for absorption
How does regional blood flow effect drug distribution
- well perfused tissue are likely to be exposed to a higher concentration of drug
- higher metabolically active tissues tend to have a greater blood flow and denser network of capillaries
What are the proportions of blood distribution in the body?
- liver 27%
- kidneys 22%
- muscles 20%
- brain 14%
- heart 4%
What % of acidic drugs tend to bind to bind to plasma proteins?
50-80%
What type of drug can albumin bind to?
ionised and non-ionised
How does ionised drug pass through the capillaries?
-small gaps between endothelial cells are aqueous and so ionised as well for the drug to pass through
WHat 3 types of capillary are there?
fenestrated- more permeable to drugs
continuous - found in normal vessels and more permeable to drugs
discontinuous- large gaps between endothelial cells
How can localisation in tissues affect distribution of the drug?
- fat is not highly perfused, they produce a very high lipophilic environment
- drugs that are lipophilic tend to localise in fatty tissues
- fat soluble drugs highly group into fatty tissues e.g. brain and testes
What are the 2 major routes of drug excretion?
- kidney
- liver
