quantitative pharmacodynamics

levodopa

treatment for Parkinson’s. restores dopamine levels in the brain.

why is levodopa used instead of dopamine to treat Parkinson’s disease?

dopamine cannot cross the blood-brain barrier, and L-DOPA is the precursor to dopamine in the biosynthetic pathway and can cross the barrier.

what is used in combination with L-DOPA and why?

carbidopa. because it inhibits dopamine, preventing L-DOPA turning into DOPA before it has entered the brain.

what can be directly measured from dose-response curves?

EC50 (half maximal effective concentration). concentration of a compound that gives half-maximal response.

full agonists

drugs whose maximum response is the largest a tissue or cell is capable of giving (i.e. they have high efficacy)

partial agonists

drugs whose maximum response is lower than this (even when they occupy all the available receptors)

reversible drug binding

almost all agonists bind reversibly to the receptor, weak chemical bond, dissociates readily. many antagonists bind reversibly to the receptor.

competitive antagonists

antagonists have high affinity but no efficacy. a competitive antagonist can be displaced from the receptor by increasing the concentration of the agonist.