Pharmokinetics Flashcards
What factors can affect the pharmaceutical process?
The formulation of the drug (tablet/liquid) and the compliance of the patient.
What is the name of the process by which a drug gets to its site of action?
Pharmacokinetic
What is a pharmacodynamic process?
This is the process by which a drug exerts it’s therapeutic effect.
How can we reduce systemic side effects?
We can change site of administration so that the drug is more targeted to where it is needed.
What is oral bioavailability?
This is the proportion of drug given which reaches the systemic circulation unchanged.
What is LD50?
This is the maximum tolerated dose of a drug.
How can we calculate therapeutic ratio?
LD50/ED50, where ED50 is the minimum effective dose.
What consideration needs to be made to drugs being given at intervals?
This means that drug concentrations in the systemic system will fluctuate, and this must be maintained below the toxic concentration.
What factors alter the pharmacokinetic process of a drug?
1st pass metabolism and absorption in the gut.
Name three routes of drug administration which avoid 1st pass metabolism
Rectal, sublingual and Parietal (e.g. IV, IM/SC)
What is volume of distribution?
This is a theoretical volume in which a drug has become distributed throughout if this happened instantaneously. This will vary depending on how lipid soluble a drug is.
In what cases can drug bind to receptors?
When the drug is free and not bound to any other plasma proteins.
What are the potential problems with drugs binding to proteins?
If there is a high percentage of binding, or if the therapeutic ratio is small or the volume of Distribution is small then displacement of drugs from plasma proteins can be very detrimental.
What is the difference between a class I and class II drug?
A class one drug is used at lower conc than the number of binding sites while a class II drug is used at higher concentrations and so displaces the class I drug.
What is another name for a class II drug?
Precipitant.
How is the steady state of a drug quickly reached?
Free drug levels rise, and with this, receptor action also rises. Elimination rate rises and so steady state is restored.
What is 1st order kinetics?
This is when elimination rate is proportional to drug concentration.
What controls 0 order kinetics?
This is controlled by the number of elimination sites, and it where the same amount of drug is eliminated per unit time with no changes caused by changing concentrations.
How many half lives are needed with repeated drug administration to reach steady state for a 1st order kinetic drug?
5
If we want a fast action for a drug with a long half life, what do we administer?
We can administer a large loading dose, and then smaller maintenance doses.
How can drugs be eliminated from the body?
They can be metabolised in the liver or excreted by the kidneys
Why are mixed functional oxidases in the liver important?
These have low specificity, affinity for lipid soluble drugs and are inducible and inhibitable
When are drug interactions in metabolism important?
When min drug conc is used, when there is a low therapeutic ratio or when metabolism follows zero order kinetics.
What can cause quicker drug degeneration?
Enzyme inducers
When are enzyme inducers a problem?
They cause problems when drugs are used at low concentrations
What can enzyme inhibitors cause?
These can cause toxic drug levels to present.
What fraction of drug can be excreted in the kidneys?
Only the free fraction is affected by the kidneys
What factors affect the amount of lipid soluble drug reabsorbed in the kidney? Where in the kidney may this occur?
pH and concentrations, this can occur in the collecting duct.
What ionisation state must a lipid soluble drug be to be reabsorbed in the kidney?
Non ionised
If a drug is a weak acid, what state must the urine be for increase reabsorption?
Acidic so that the drug is in its non-ionised form
When a drug is a weak base and present in acidic urine, will there be increase or decreased reabsoprtion?
Decreased because more of the drug will be in the ionised form and therefore unable to cross the phospholipid bilayer.
What two effects does renal disease have on a drug?
It increases the half life and therefore increases the time take to reach steady state.
