Drug Absorption Flashcards
Define Pharmaceutical process
Get the drug into the patient
Define Pharmacokinetic process
Get the drug to the site of action
Define Pharmacodynamic process
Produce the correct pharmacological effect
Define Therapeutic process
Produce the correct therapeutic effect
What determines drug pharmacokinetics
Absorption
Distribution
Metabolism
Elimination
What are the methods of administration?
Oral Subcutaneous Intramuscular Other GI - Sublingual, rectal Inhalation Nasal Transdermal
What does absorption involve
Drugs must enter blood stream and distributed to site of action
What does ADME allow?
understanding of: Dosage Drug administration Drug handling Patient variability Potential for harm.
What is sublingual?
Under the tongue
Oral absorption
What is Tmax?
The time to peak concentration
Oral absorption
What is Cmax?
The peak concentration
Oral absorption
What is the (AUC)?
The area under the drug concentration-time curve
Does the dose effect the tmax?
No, alters cmax
What does the The area under the drug concentration-time curve represent?
The amount of drug which reaches the systemic circulation
What is the Therapeutic range?
The range of concentrations at which a drug is active.
What happens above or below the therapeutic range
Toxicity
Insufficient/no pharmalogical action
What does The AUC allows us to estimate?
BIOAVAILABILITY - extent and rate at which drug reaches systemic circulation.
What is the bioavailability of an intravenous drug?
100%
What are the factors affecting Bioavailability? (oral absorption)
Formulation
Ability of drug to pass physiological barriers
- Particle size
- Lipid solubility
- pH and ionisation
Gastrointestinal effects
- Gut motility
First pass metabolism
What is dissolution?
The rate a drug breaks up
What is an example of a physiological barrier?
Transport across membranes
What are the methods of transport across membranes?
Passive diffusion
Filtration
Bulk flow
Active transport
What does the degree of the ionisation of the drug depend on?
pH of the environment
What form of the drug crosses the membrane?
The unionised form
What is the distribution of the un-ionised form of a drug?
Distribute across the membrane until equilibrium reached - equal concentration on each side.
Where will an acidic drug be most concentrated?
In the compartment with high pH
What does the Henderson-Hasselbalch equation describe?
The relationship between the local pH and the degree of ionisation
What is The ability of a drug to diffuse across a lipid barrier is expressed as?
lipid-water partition coefficient
What is the lipid-water partition coefficient?
The ratio of the amount of drug which dissolves in the lipid and water phase when they are in contact.
What factors effect passive diffusion
Molecular size
Lipid solubility
Polarity
Ionisation
pH
Describe Active Transport in drugs
Energy dependent
Against conc gradient
drug reversable bound to barrier system
What is the structure of drugs that undergo active transport?
They must resemble naturally occurring compounds
Describe facilitated diffusion
Occurs along the concentration gradient Require carriers Structure specific No energy required
Where does filtration occur?
Through channels in the cell membrane.
What is the molecular size of the drug in Filtration / Bulk Flow/ Pore Transport?
Low molecular size
What is the driving force in Filtration / Bulk Flow/ Pore Transport?
Hydrostatic or the osmotic pressure
What is first pass metabolism
Metabolism of drug before reaching systemic circulation
What can cause first pass metabolism
Limit on oral drug route
Gut lumen
Gut wall
Liver
How can first pass metabolism be avoided
Subcutaneous
Inhilation
Sublingual absorption
Transdermal
Rectal
What does bio phase mean?
The effect site of the drug
