Deck 1 Flashcards
- Q. Describe the difference between pharmacokinetics and pharmacodynamics
A. Pharmacokinetics refers to the effect of the body on the drug while pharmacodynamics refers to the effect of the drug on the body.
- Q. What is a ligand?
A. A drug which binds to a receptor is termed a ligand
- Q. Describe the difference between agonists and antagonists? What is an inverse agonist?
A. Agonists initiate a biological response, usually by binding to and activating receptors. (drug agonists can occasionally be used to inhibit receptor function through desensitization).
B. Antagonists reduce the effects of an agonist
C. An inverse agonist activates a receptor but induces the opposite pharmacological response to the agonist (agonist = yes, inverse agonist = no, antagonist = no response)
- Q. What is a selective agonist? What is a competitive antagonist?
A. A selective Agonist is selective for a specific type of receptor eg, buspirone is a selective agonist for serotonin 5-HT1A
B. A competitive antagonist is a receptor antagonist that binds to a receptor but does not activate the receptor; the antagonist competes with the available agonist for receptor binding sites on the same receptor.
- Q. What does a log concentration response curve show?
A log concentration response curve shows the potency of an agonist, EC50 is a concentration that gives half the maximal response
- Q. What does efficacy mean to agonists? What is intrinsic efficacy?
A. For agonists the term efficacy is used to define the maximum response
B. Intrinsic efficacy is the property of a drug that determines the amount of biological effect produced per unit of drug-receptor complex formed. Two drugs that bind to the same sets of receptors may not produce an equal effect; even if both agents are given in maximally effective doses. This is because the agents differ in their intrinsic activities and the one producing the greater maximum effect has the greater intrinsic activity.
C. Intrinsic activity = Emax of partial agonist/Emax of full agonist (on a log concentration response graph)
- Q. How do histamine and mepyramine act as agonists and antagonists in the ileum?
A. Histamine acts as an agonist by binding to receptors and initiating ileum contraction (H1) and acid secretion from parietal cells. (H2)
B. Mepyramine acts as an antagonist as reverses the ileum contraction (H1 receptor), however has no effect on acid secretion. (H2 receptor). H2 blockers are also called histamine H-2 receptor antagonists because they bind to H2 receptors eg cimetidine.
- Q. Define affinity and efficacy
A. Affinity is how well a ligand binds to a receptor (agonists and antagonists)
B. Efficacy describes how well a ligand activates a receptor (antagonists have 0 efficacy)
- Q. What is allosteric modulation?
A. When an allosteric ligand binds to an allosteric receptor site close to the agonist binding site there may be modulation to the affinity of the agonist binding
- Q. What is tolerance? What occurs during withdrawal?
A. A reduction in drug effect over time (continuous, repetitive, high concentrations)
B. Agonists tend to temporarily reduce their receptor number overtime leading to tolerance
C. Antagonists tend to temporarily increase their receptor number leading to overactivity on withdrawal
- Q. What is a prodrug?
A. Prodrugs are biologically inactive compounds which can be metabolised in the body to produce an active drug
- Q. What are the three phases of pharmacokinetics at the plasma level?
A. Uptake into the plasma
B. Distribution from the plasma
C. Elimination from the plasma
- Q. What is the volume of distribution of a drug?
A. The theoretical volume in litres that would be necessary to contain the total amount of an administered drug at the same concentration that is observed in the blood plasma
B. It represents the degree to which a drug is distributed in the body tissue rather than the plasma (a higher volume of distribution indicates a greater amount of tissue distribution)
C. Non-polar drugs with low rates of ionization and low plasma binding capabilities have higher volumes of distribution. (volume of distribution may be increased by renal failure due to fluid retention and liver failure – or decreased in dehydration)
D. VD = total amount of drug in the body / drug blood plasma concentration
E. A small VD is ideal as it means that it is easy to reach steady state and plasma concentration ‘responsive’ to dose rate
- Q. How may drugs move between compartments? How might pH affect movement?
A. Simple diffusion, facilitative diffusion, active transport, through extracellular spaces, non-ionic diffusion
B. Non-ionic diffusion is enhanced if the adjacent compartments have a pH difference
- Q. What is bioavailability?
A. Bioavailability refers to the amount of drug taken up as a proportion of the amount administered
