11-12. pharmacodynamics 1-2

what does affinity describe? what does it NOT describe?

• describes how well a ligand binds a receptor

• does NOT describe receptor activity elicited by a ligand

what is the equilibrium dissociation constant (K_d)? what does a small K_d mean?

• value used to quantify affinity

• the concentration of ligand needed to occupy half the receptors at equilibrium

  • small K_d = high affinity

what is potency? how is it measured?

• amount of drug needed to produce a response (measured in molar concentration)

• measured by the effective drug concentration needed to produce the half-maximal response

  • EC₅₀ or ED₅₀

what is intrinsic activity (aka efficacy)? how is it measured?

• ability of a ligand-receptor complex to elicit a biological response

• measured by the maximal response elicited by a receptor (E_max)

full agonists have ____ affinity, ____ intrinsic activity

high affinity, high intrinsic activity

partial agonists have ____ affinity, ___ intrinsic activity

high affinity, low intrinsic activity

competitive antagonists have ___ affinity, ___ intrinsic activity

high affinity, no intrinsic activity

non-competitive antagonists have ____ affinity, ___ intrinsic activity

affinity for different site than endogenous agonist, no intrinsic activity

which type of antagonist cannot be overcome by increasing agonist concentration?

non-competitive antagonists → bind to receptors at different site than agonists; prevent agonists from activating receptor

physiological antagonist

• drug that counters the effects of another by binding to a different receptor and causing opposite effects

• ex. glucagon & insulin

chemical antagonist

• drug that counters the effects of another by binding the drug and preventing its action

• ex. chelators given in cases of lead poisoning

what does a quantal dose-response curve measure?

cumulative population distribution responding to the drug

what does therapeutic index measured? how is it calculated?

measures relative drug safety