Drug Absorption Flashcards
To have biological action; what must a drug do in the body?
Enter the blood stream and be distributed at the site of action
List the modes of administration
Hint: There are nine
Oral, Intravenous, Subcutaneous, Intramuscular, Sublingual, Rectal, Inhalation, Nasal, Transdermal
The process of drug action can be broken into four steps - what are those steps?
Absorption, Distributionm Metabolism, Elimination
Understanding the action of a drug enables us to understand what other processes?
Dosage, drug handling and administration, patient variability and the potential for harm
What is the definition of drug absorption?
The process of movement of unchanged drug from the site of administration to the systemic circulation
There is always a correlation between plasma concentration of a drug and the __________ _______ .
Therapeutic response
What is the Tmax?
The time to peak concentration of a drug
What is the Cmax?
The peak concentration a drug reaches in the blood
What does the Area under the Curve of a drug concentration-time graph represent?
The amount of drug that reaches the systemic circulation
Describe what is meant by therapeutic concentration
A drug is effective over a range of concentrations
How is the therapeutic range measured?
Using the therapeutic index
Describe what occurs if concentration of a drug falls outside of its therapeutic range
Above the range - toxicity
Below the range - insufficient/no pharmacological action
What is bioavailability?
A mesure of the AUC which shows how much of the drug has been delivered to the systemic circulation and is available at the site of action
Why percentage of bioavailability does a drug have that has been introduced intravenously?
100%
List the factors effecting bioavailability
Formulation, ability to pass barriers, GI effects and first pass metabolism
What is formulation?
The way the drug is designed - e.g. slow release preparations
What factors effect a drugs ability to pass biological barriers?
Particle size, lipid solubility and pH due to ionisation
What factos constitute the GI effect on drug absorption?
Gut motility, Presence of food and illness
What is first pass metabolism?
Metabolism of a drug before its reached the systemic circulation
How is first pass metabolism typically mechanised?
Enzymes
What mode of administration is particularly effected by first pass metabolism ?
Oral route
How does ionisation effect the permeability of drugs across barriers?
Ionised drugs cannot pass through membranes by diffusion
How should ionised drugs behave? (Hint: Think about tonicity)
They should equilibrate in concentration across the membrane in order to not effect osmosis
How is the degree of ionisation worked out?
Henderson-Hasselbalch Equation
How is the lipid solubility of a species expressed?
A lipid-partition coefficient
What is the lipid-partition coefficient?
The ratio of the amount of the drug which dissolves in the lipid and water phase when they are in contact
A drug with a higher LPC will easily cross membranes. True or false?
True
