Pharmacodynamics

Quantifying drug-receptor interactions

D = interaction of a drug R = receptor

Drugs bind to receptors at a rate proportional to drug concentration.

Rate at which they unbind is dependent on chemical properties of drug-receptor complex.

Law of mass action implies that…

  • Forward rate is K+[D][R]

  • K+ = forward rate constant

  • Reverse rate is K-[DR]

  • K- = Reverse rate constant

This can be use to derive the Hill-Langmuir equation

p = proportion of receptors occupid by a drug Kd = ratio k-/k+

Kd = drugs's association constant from its receptor = concentation at which, at equilibrium, half the rceptors will be bound with a drug.

2 ways to plot a concentration binding curve:

Affinity = affinity of a drug for its receptors

Measured using Kd.

Actions of drugs at receptors:

  • Agonist = chemical (drug, hormone, neurotransmitter or oother signalling molecule) that binds to its target to increase its activity

  • Antagonist = chemical that opposes action of another chemical

    In the absense of an agonist, antagonists should have no action on their targets

  • Endogenous agonist = substance naturally produced by the body that binds to and activates a specific receptor, resulting in a physiological response.

    • E.g. hormone, continuousy present in the body

    • Agonists like propanolol will cause physologcal effects by themselves