Drug Absorption Flashcards
What is pharmaceutical process?
Getting the drug into the patient
What is pharmacokinetic process?
Getting the drug to the site of action
What is pharmacodynamics process?
Producing the correct pharmacological effect
What is therapeutic process?
Producing the correct therapeutic effect
What are the 4 basic factors that determine pharmacokinetics?
Absorption
Distribution
Metabolism
Elimination
A knowledge of the factors of pharmacokinetics enables an understanding of what?
Dosage
Drug administration
Drug handling
Patient variability
Potential for harm
What must most drugs do to have biological action?
Enter the blood stream and be distributed to a site of action
What are different methods of administration?
Oral
Intra-venous (IV)
Subcutaneous (applied under the skin)
Intramuscular
Other GI (sublingual, rectal)
Inhalation
Nasal
Transdermal (delivered across the skin)
What is absorption?
Process of movement of unchanged drug from the site of adminstration to the systematic circulation
What does absorption depend on?
Properties of the drug
Dosage used
Anatomy and physiology of the drug absorption site
What is the relationship between plasma concentration and the therapeutic response?
There is a correlation between the two
What is Cmax?
The peak concentration
What is T max?
The time to peak concentration
What does the area under the curve of a concentration/time graph represent?
Total amount of drug that reaches systematic circulation
What does Tmax tell us?
How quickly the drug is going to get into our circulation to produce an effect
What does Cmax tell us?
Whether the effect of a drug may be toxic or ineffective
What does increasing the dose do in relation to Tmax and Cmax?
Does not increase Tmax but increases Cmax
What is the therapeutic range?
The range of concentration that a drug is active
What happens above the therapeutic range?
The drug is toxic
What happens below the therapeutic range?
The drug is ineffective
What is bioavailability?
The amount of a drug that gets into circulation and is available for biological activity
What is the bioavailablity of a drug given intra-venously?
100% bioavailability
How is bioavailability determined?
By giving the drug and working out the toal amount over time then comparing this to the IV route
What are some factors that affect bioavaiability?
Formulation
Ability of drug to pass physical barriers
Gastrointestinal effects
First pass metabolism
What impacts a drugs ability to cross physical barriers?
Particle size
Lipid solubility
pH and ionisation
What must a drug be to dissolve in lipids?
Unionised
What does first pass metabolism refer to?
Removal of the drug by the liver
What is bioavailability used to work out?
The best dosage of a drug for the desired effect
What are different kinds of transport across physical barriers?
Passive diffusion
Filtration
Bulk flow
Active transport
Facilitated transport
Ion-pair transport
Endocytosis
What does the degree of ionisation depend on for a drug and why?
The environment because most drugs are weak acids or bases
When does an unionised drug stop crossing a membrane?
Once equilbrium is reached
What may happen whilst a drug is in the middle of crossing a membrane?
Ion trapping
What is ion trapping?
Drug crosses the first membrane but then is ionised and cannot cross the second
Where do acidic drugs get stick?
In compartments with a high pH
What is the ability of a drug to diffuse across a lipid barrier expressed as?
Lipid-water partition coefficient
What must a drug be to diffuse across a lipid membrane?
In solution
Lipid soluble
What is the lipid-water partition coefficient?
Ratio of the amount of drug which dissolves in the lipid an water phase when they are in contact
How are drugs given that cannot diffuse across lipid membranes?
By IV to skip most of these barriers
Where does passive diffusion occur?
Along concentration gradients (requires no energy)
What does passive diffusion depend on?
Lipid solubility
Degree of ionisation
Where does facilitated diffusion occur?
Along the concentration gradient but requires carriers
What are examples of things that use facilitated diffusion?
Monosaccharides
Amino acids
Vitamins
Where does active transport occur?
Against concentration gradients (requires energy)
What are examples of things that use active transport?
Ions such as K, Na and Ca
Where does filtration occur?
Through channels in the cell membrane
What is the driving force of filtration?
Hydrostatic pressure or osmotic pressure difference across the membrane
What uses filtration?
Urea
What are gastrointestinal factors that affect drug absorption?
Motility (speed of gastric absorption)
Food (can enhance or impair absorption)
Illness (can increase or decrease absorption)
Where are most drugs absorbed?
Small intestine
What is first pass metabolism?
Metabolism of drug prior to reaching systematic cirulation
What are some places involved in first pass metabolism?
Gut lumen (acid, enzymes)
Gut wall (metabolic enzymes)
Liver (hepatic enzymes)
What does absorption from subcutaneous/intramuscular sites depend on?
The blood flow at these sites
What do drugs given subcutaneously or intramuscularly avoid?
First pass metabolism
What do sublingual drugs avoid?
First pass metabolism
What is sublingual?
Under the tongue
What do drugs given via the rectum bypass?
First pass metabolism
What is the absorption of a drug from the rectum like?
Slow
What kinds of drugs are often given via the rectum?
Ones that cause irriation to the stomach
What is inhalation best for?
Volatile agents
How much of an inhalation drug is absorbed?
5-10%
What are the advantages of transdermal drugs?
Avoids first pass metabolism and can provide a controlled release
What should be considered when deciding the mode of administration?
Purpose and site of drug action
Disease effects
Patients ability to take medicine
Speed of action
Reliability of absorption
