Pharmacokinetics Flashcards
What do drug effects depend on?
The mechanism of action and effects on cellular proteins, receptors, ion channels, enzymes and transporters
The drugs physiochemical properties; affinity, efficacy and potency
The concentration
What is meant by absorption?
How the drug enters the body
What is meant by the distribution of the drug?
Compartments and how it reaches the targets
What is meant by the metabolism of a drug?
How it is processed in the body
What is meant by the excretion of a drug?
How the drug leaves the body
How might a drug be distributed in the body?
Bulk flow in the bloodstream via the cardiovascular system
Diffusion eg has to cross blood vessels
The diffusion co-efficient of a drug is related to what?
Its size; it increases if the molecule is small
Larger molecules take longer to diffuse
How is lipid solubility measured?
With the partition co-efficient- this is how easily a drug dissolves into a lipid space vs an aqueous space
What property of a drug makes it dissolve freely?
if it is uncharged
Increasing how easily a drug dissolves causes what to increase in the body?
The rate of absorption from the gut increases
The rate of penetration into the brain and other tissues increases
Renal elimination also increases
What are the ways that drugs can be adinistered?
Intravenous, Intramuscular, Intrathecal, Inhalation, Oral/Ractal, and the percutaneous route
Describe what happens to drugs that are administered intravenously?
Drugs enter the plasma
Can be exctreted via sweat and milk (from breast)
Avoids gut metabolism
Needs a qualified practioner for administration
Describe what happens to drugs that are administered intramuscularly?
From muscle drugs travel to plasma
Avoids metabolism in the gut
The rate of absorption depends on which muscle is is injected
An example is insulin
Describe what happens to drugs that are administered Intrathecally?
Drug is injected into the CSF which goes to the brain and plasma
Drug is injected into the spinal cord
Used when drugs for CNS are required and when only a regionable effect is required
Used to administor local anaestetic for child birth - ideal as the drug does not want to be passed on to the baby
Describe what happens to drugs that are administered through inhalation?
Drug goes directly to the lungs
This is viable for gases only eg general anaestetics
Target for action can also be in the lungs eg in asthma
Describe what happens to drugs that are administered orally or rectally?
Most desirable due to easy administration
The drug has to pass through the gut
Diffusion across the intestines depends on gut motility and capsule size
Capsules can cause both fast and slow absorption depending on the rate required
What is meant by the term bioavailability?
The fraction of the ingested drug as part of the fraction in the plasma eg how much of the drug ends up in the plasma?
Describe what happens to drugs that are administered via the percutaneous route?
Drugs go through the skin eg it is applied on patches
Absorption across the skin is slow and poor but is useful for slow and continuous conditions
Example opiate patches for the brain
