Pharmokinetics Flashcards
What are the enteral methods of drug administration
Oral
Rectal
Sublingual (under the tongue)
What are the parenteral methods of drug administration
Subcutaneous (under the skin)
Intramuscular
Intravenous
What is pharmokinetics
The kinetic change of the drug in the body overtime
What is first pass metabolism
Enteral drugs would pass through the liver and they would be metabolised before hey pass through to the systematic circulation
What is the transcellular and the paracellular drug movement
Transcellular is through the cells
Paracellular is between the cells
What is distribution
The movement of the drug in systematic circulation and to the tissues and the organs
What is bioavailability
The amount of drug that would pass through to the systematic circulation and into the tissues
How do you calculate bioavailability through the graphical information
Fo = AUC (oral) / AUC (intravenous)
What conditions are necessary for a drug to pass through the membrane
Small
Unionised
PH
Hydrophobic
Lipid based (lipodicity)
What conditions would be needed for a drug to be unionised
Acid PH environment and weak acid drug = unionised
Basic PH environment and weak base drug = unionised
What does the Henderson-hasslebalch equation show
The estimated PH
What is the Henderson-Hasslebalch equation for acids and bases
PH - PKA = ionised / unionised (acids)
PH-PKA = unionised / ionised (bases)
What factors would influence the drug dosage
Body surface area
Mass
Age (older you get the lower the amount of water in the body)
How would you calculate the volume distributed
Vd = drug dosage / plasma concentration
What is important about plasma proteins
Can bind to the drugs
Albumin can bind to the acidic and neutral drugs
AAG (glycoprotein) binds to the basic drug
What is the transmission time and suitable PH for the small intestine
3-5 hours
PH 6-7
What is important about the small intestine
The main area for drug absorption
What contributes to elimination
Metabolism and excretion
What is the main metabolising enzyme that would metabolise 50% of all the top drugs
CYP3A4
What is the extraction ratio
That amount of the drug that would be metabolised and removed from the body
What does it mean if the extraction ratio is high
Large amount of drug would be metabolised and released from the body
What does it mean if the extraction ratio is low
Low amount of drug would be metabolised and removed from the body
What is meant by clearance
The volume of fluid or blood from which a drug would complete be removed
What would happen to the clearance is there was renal or hepatic failure
The clearance would decrease as would have no functioning liver or kidney to remove the drug from the blood and the fluid
What are the inhibitors and the inducers of enzyme action
Inhibitors would reduce the amount of drug that is metabolised (for example grape fruit juice)
Inducers would increase the rate of drug metabolism (st johns wort)
What causes the half life to increase
Decreased clearance
Decreased volume distribution
What is half life
The amount of time taken for the concentration of drug to half
What is first order kinetics
The rate of break down and the concentration of the drug would be directly proportional
What it is the loading dose
The first dose that would be give to patients
This would be larger then the normal dose as would want to reach the therapeutic dose level and then allow this level to be maintained
What would happen in the body if there was no drug clearance
Drug accumulates, toxicity of the drug, death
What is liver perfusion
The amount of drug that would move through the liver within the blood or in the plasma (fluids)
When is perfusion important
When would have a high extraction
Means large amount would pass through the liver
Low amount of active drug within the body
When is perfusion not important
When there is a low extraction
The amount that passes through the liver would not matter not a lot would be metabolised
Large amount of the active drug would be in the body
What is drug metabolism by oxidation
Changing the functional group
Makes the molecule polar
Can be removed by the renal system
What is drug metabolism by conjugation
Adding a functional group
Allows the molecule to increase in size
Less polar
Then can have billiary excretion (in stool)
How would the use of St. John’s wort (a CYP 3A4) effect the plasma concentration and why
Decreases the plasma concentration
Would allow the increased metabolism of the drug,so would have less available in the system
What methods are used in transcellular movement of drugs (through the cells)
Diffusion
Carrier mediated transport
Bulk transport
Endocytosis
