Drug absorption Flashcards
Pharmaceutical process
Get the drug into the patient
Pharmacokinetic process
Get the drug to the site of action
What are the four basic factors determine drug pharmacokinetics
Absorption
Distribution
Metabolism
Elimination
Define absorption
the process of movement of unchanged drug from the site of administration to the systemic circulation
What are the different routes drugs can be absorbed into the blood stream
Oral Intravenous Subcutaneous Intramuscular Other GI - Sublingual, rectal Inhalation Nasal Transdermal
How does increasing the dose effect time and concentration
does not affect the time at which peak concentration is reached but does increase the peak concentration
Does increasing the concentration of drug increase the rate of the reaction
no
What is the therapeutic index
measure of the range at which a drug is safe and active
What is the therapeutic range
A drug is active over a range of concentrations
what is BIOAVAILABILITY
an estimate of the amount of drug which reaches the circulation and is available for action
Which route of administration gives 100% bioavailability
IV
What are the factors affecting bioavailability
Formulation
Ability of drug to pass physiological barriers
Gastrointestinal effects
First pass metabolism
Define desolation
What is modified release
when the drug breaks up
Slow release of drugs passing from GI tract
The ability of drugs to pass physiological barriers is dependant on drugs
Particle size
Lipid solubility
pH and ionisation
What are the different methods drugs are transported across the membrane
Passive diffusion Filtration Bulk flow Active transport Facilitated diffusion Ion-pair transport Endocytosis
What kind of drugs cant cross membrane
ionised drugs as aren’t lipid soluble
Where is an acidic drug more likely to be trapped
compartment with high pH
Changing the pH of an environment can alter the ionisation of the drug affecting the rate of
absorption or diffusion
The ability of a drug to diffuse across a lipid barrier is expressed as a
lipid-water partition coefficient
To undergo active transport drugs must resemble
naturally occurring compounds
How does bulk flow transport occur
Occurs through channels in the cell membrane and is dependant on the blood flow
What is the driving force of bulk flow
driving force for the passage of the drugs is the hydrostatic or the osmotic pressure difference across the membrane
What Gastrointestinal Factors effect drug absorption
Motility - speed of gastric absorption
Food - enhance or impair absorption
Illness - eg diarrhoea, drugs go straight through you
or some illnesses will enhance absorption
Define first pass metabolism
Metabolism of drug prior to reaching systemic circulation
What route can avoid first pass metabolism
IV
Sublingual
Rectal
transdermal
What does a migraine reduce
the rate of stomach emptying therefore decreasing absorption rate
What are the benefits of IV
needs small volume
can change the rate of absorption from sites with physical properties
gives 100% bioavailability
Avoids first pass metabolism
What administration route allows drugs to enter circulation directly
sublingual
What is an advantage and disadvantage of rectal administration
dis - absorption tends to be slow
adv- prevent drugs causing irritation of the stomach
Where will inhalation administration be metabolised
in the lungs
When is inhalation usually used
topical effect
avoid problems of oral absorption (eg nausea)
for rapid action
What is an advantage and disadvantage of transdermal
adv - provides a controlled release
dis - few substances are well absorbed
Considerations for mode of administration
Purpose and site of drug action -Local absorption -Avoid first pass metabolism Disease effects Patients ability to take medicine Speed of action Reliability of absorption
What can cause local metabolism
Sublingual
Inhalation
rectal
Where are drugs absorbed from
GI tract
