Drug Pharmacokinetics Flashcards
What is the therapeutic index?
Therapeutic index: ratio between
• Concentration that achieves a therapeutic response
• Concentration that achieves a toxic effect
Is it good to have a wide or narrow therapeutic index?
Wide
What does the mnemonic ADME stand for in pharmacokinetics ?
Absorption
Distribution
Metabolism
Excretion
Describe absorption in relation to drug pharmacokinetics
drug entering the body and reaching the systemic circulation
Describe distribution in relation to drug pharmacokinetics
how the drug moves from the systemic circulation to reach the target tissues
Describe metabolism in relation to drug pharmacokinetics
How the drug is chemically altered by the body - usually this alters the drug characteristics to facilitate excretion.
Describe excretion in relation to drug pharmacokinetics. How is this most commonly achieved?
how the drug is removed from the body, most commonly this is achieved via concentration in bile or urine.
What are the 2 main divisions of drug delivery routes?
Local administration
Systemic administration
When is local administration of a drug used?
When the site of action of the drug is readily accessible
When is systemic administration of a drug used?
When:
o Tissue may be inaccessible AND/OR
o Widespread distribution of drugs is necessary
What is the most common route of drug delivery in systemic administration of a drug?
Oral
List 3 principles of selecting an appropriate drug route
Route must provide adequate delivery of the drug
Must be acceptable for the patient
Should minimise adverse drug effects
List advantages of IV administration
Absorption is instant
Absorption is trivial - can be affectively ignored
Rapid systemic delivery of drug
Describe subcutaneous/intramuscular administration
Only small volume can be given
Similar to IV, but slower onset of action
May be painful/unpleasant for patient
Requires training and equipment
What is an advantage of oral administration?
It is the most simple and convenient method of drug administration
In what 3 cases would oral administration not be chosen?
If drug is digested or poorly absorbed
If drug is irritant to stomach
If very rapid onset of action is required
What happens if a drug remains bound to a plasma protein? effect on volume of distribution?
It remains in the circulation and has a small volume of distribution
What happens if a drug has a high degree of lipid solubility? effect on volume of distribution?
It is more widely distributed in the tissues.
High volume of distribution
calculation for dose of a drug =
Dose of a drug = Concentration x Volume
calculation for Loading dose of a drug =
Loading dose = Dose/kg x Body weight
What is the calculation for a top up dose?
Top up dose = change in conc x volume of Distribution
Define Bioavailability
Bioavailability = fracture of the drug reaching systemic circulation after oral administration
In what way can absorption or distribution of drugs be improved?
By using pro-drugs
What can pro-drugs allow?
they allow a drug that would not otherwise be suitable for oral administration to be given by this route
What are the 2 barriers that oral administration presents to absorption into the systemic circulation?
absorption into the portal circulation from the intestine
passage through the liver to enter systemic circulation (first pass metabolism - reduces drug concentration)
what is a modified release delivery system?
a delivery system designed to slow the absorption of a drug to provide a smoother profile of drug concentration (so no high peaks and low troughs)
