Affinity

Affinity is a measure of the rate at which a ligand binds to a receptor. A drug with high affinity for a receptor binds to the receptor at low concentrations, whereas a drug with low affinity for a receptor binds to the receptor at high concentrations. Drugs that have higher affinity for a receptor tend to be more potent and efficacious and hence to have stronger effects than drugs with lower affinity, although there are many different factors that determine potency and efficacy in a given drug.