Assessment of Receptor Occupation

Measure of Affinity

kd is a relative measure of affinity, or 'stickiness' of a drug for its receptor. It varies inversely with the affinity of the drug for its receptor and typically is in the single digit nanomolar range for most drug molecules.

High-affinity drugs have lower kd values and occupy a greater number of drug receptors at a given concentration than do drugs possessing lower affinities.