Drug Absorbtion 1 Flashcards
Define Pharmaceutical Process?
Getting the drug into the patient
What is it called “getting the drug to the site of action in the patient”?
The pharmacokinetic process
What is the pharmacodynamic process?
Producing the correct Pharmocological effect with the drug.
{What is the therapeutic process?
Producing the intended therapeutic response?
What determines pharmacokinetics?
[ADME}
Absorption
Distribution
Metabolism
Elimination
Define Absorption:
Process of movement of unchanged drug from site of administration to sytemic circulation.
Try name 9 drug application routes. Go on i fucking dare you
Oral Subcutaneous/Intramuscular Inhalation/nasal Transdermal (skin patches) IV Topical (creams etc) Sublingul (under tongue) Rectal
Define therapeutic range:
The range of blood [drug] over which a drug is active
What happens if drug conc. is above or below the therapeutic range?
If its above the range toxicity occurs
If its below the range theres insufficient pharmacological action
Define Therapeutic Index (TI):
A comparison of the drug conc. level that causes the therapeutic effect against the amount that causes toxicity.
What two things must you consider concernin the rate of oral absorption?
Amount of drug entering systemic circulation and speed at which it happens
What is Tmax?
The time to peak drug conc. in systemic circulation
What is Cmax?
The peak drug conc. in systemic circulation
What is the AUC?
The area under a drug conc vs time curve.
I.e. the amount of drug reaching circulation
How does increasing the dose affect Tmax & Cmax?
Increasing the Dose has no effect on Tmax but increases Cmax.
Define Bioavailability?
Amount of Drug reaching circulation & available for action
What method of drug administration has 100% bioavailability?
Intravenous Drugs have 100& bioavailability.
What 4 factors effect Bioavailability?
- Formulation
- First pass metabolism
- Gastrointestinal effects
- Ability of drug to pass physiological barriers.
How does formulation affect bioavailability?
Some drugs are prepared for slow release
What 3 gastrointestinal effects alter bioavailability?
- Illness & Dsease
- Gut Motility
- Food
What 3 areas affect the ability of a drug to pass physioloical barriers?
- pH & Ionisation
- Lipid Solubility
- Particle Size
Define First pass metabolism?
The amount of drug metabolised by the gut before it is absorbed into systemic circulation
What does passive diffusion rely on?
Lipid solubility
Degree of ionisation
Why does drug ionisation affect passive diffusion?
Only unionised drugs can pass through membranes as ionised arnt lipid soluble
What does the degree of ionisation rely on?
Local pH
i.e. an acidic drug will ionise in an alkaline enviroment
What is the henderson-hasselbach equation used for?
The relationship between local pH and drug ionisation
To what degree do pH changes affect drug ionisation?
Small pH changes can cause significant changes to drug ionisation & therfore diffusion rates.
What is the lipid-water partition coefficient?
The ability of a drug to diffuse across a lipid barrier
ratio of drug dissovled in lipid vs water phase when in contact
Exapli active absorption
Active absorption is unusual, occurs aainst the conc. gradient, is specific and requires carriers/energy.
Example of drugs moved by active absorption:
Iron, potassium, sodium, calcium
Also levodopa uptake by the brain
Explain Facilitated Diffusion:
Along conc. gradient
Needs carriers but not energy
Mizxed order kinetics
Examples of drugs moved by facilitated diffusion:
Monosaccharides
AminoAcids
Vitamins
What drives filtration/bulk flow across membranes?
Hydrostatic or osmotic pressure difference across the membrane
How does Gut motility affect the rate of dru absorption?
The faster the gastric activity the faster the drug reaches the site of absorption
What effects can food have on drug absorption?
Food can enhance or impair absorption of some drugs
How can illness efect drug absorption?
Malabsorption can impair or inhance drug absorption rates
e..g caeliacs disease
Define First pass metabolism:
Amount of drug metabolised prior to reaching the site of absorbtion
How is drug metabolised in first pass metabolism?
By acids/enzymes in the gut lumen
By metabolic enzymes in the gut wall
By Hepatic enzymes in the liver
What affects level of first pass metabolism:
The drug
Diseases
The person
Descrive Intravenous drug administration:
- 100% bioavailability
- Avoids 1st pass metabolism
Describe Topical drug Administration:
- Can achieve local or systemic effects
- Can achieve controlled, sustained doses of drugs
- Avoids 1st pass metabolism
Descrive Inhalation drug administration:
- Drug delivered directly to site
- Rapid effect
- Small doses needed
- Reduced adverse effects
- Metabolised in lungs so only 5-10% is absorbed. (little systemic effecT)
Describe the Hendersen-Hasselbach equation:
pH = pKa + log10 (ConjugateBase/UndissociatedAcid)
