drug absorption Flashcards
what are the four basic factors determining drug pharmacokinetics?
Absorption
Distruption
Metabolism
Elimination
define the process of absorption
movement of unchanged drug from the site of administration to the systemic circulation.
true or false : There is always a correlation between plasma concentration of a drug and the therapeutic response.
true
what is important when considering oral absorption
Amount of drug which enters the systemic circulation
Speed at which this happens
what is Tmax
time to peak concentration
what is Cmax
peak conc
what is the AUC
area under the drug concentration- time curve
what does increasing the dose do in regards to tmax and max
does not affect the time at which peak concentration is reached but does increase the peak concentration
The more rapid the rate of absorption, the ……. the drug concentration peak.
earlier
what is therapeutic range
A drug is active over a range of concentrations
what is the therapeutic index
measure of the range at which a drug is safe and active.
what allows us to estimate the amount of drug which reaches the circulation and which is available for action
AUC
what are the factors affecting oral absorption?
Formulation
-Slow release preparations
Ability of drug to pass -physiological barriers
- Particle size
- Lipid solubility
- pH and ionisation
Gastrointestinal effects
- Gut motility
- Food
- Illness
First pass metabolism
what is bioavailability?
the proportion of a drug or other substance which enters the circulation when introduced into the body and so is able to have an active effect.
what are the different types of transport across membranes?
Passive diffusion Filtration Bulk flow Active transport Facilitated diffusion Ion-pair transport Endocytosis
what is lipid-water partition coefficient
The ability of a drug to diffuse across a lipid barrier
A drug that is highly lipid soluble will ……. diffuse across a cell membrane.
rapidly
for active absorption what uptake of the brain is needed
levodopa
what are gastrointestinal factors
Motility
Speed of gastric absorption will affect speed at which drug reaches site of absorption (most drugs are absorbed in small intestine).
Can be affected by other drugs, food/drink and illnesses (esp pain).
Food
Can enhance or impair rate of absorption.
Illness
Malabsorption (eg Coeliac disease) can increase or decrease rate of absorption
Migraine reduces rate of stomach emptying and therefore rate of absorption of analgesic drugs.
when would you use rectual absorption
is sued for drugs which upst the stomach
what are the 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
