1. DR. SHABANA ALI (Asso. Prof.) Kd- Dissociation constant

2. Drug Dissociation Constant (Kd) Useful measure to describe the strength of binding (or affinity) b/w receptors and their ligands Binding of drug with receptor K 1 [D] +[R] [DR] K -1 Affinity = K 1 /K- 1 Kd = K- 1 /K 1 cont.

3. Reversible reaction At equilibrium, the rate of drug–receptor complex formation [DR] = rate of drug – receptor complex dissociation K1= rate of formation of drug-receptor complex K-1= rate of dissociation of drug receptor complex

4. When binding is in equilibrium= amount of drug bound to receptor is constant Affinity = ratio of k1 and K-1 Kd = the equilibrium dissociation constant & is reciprocal of affinity  The term used to describe the affinity of drugs to receptors  Relationship b/w Kd & affinity is inverse  Smaller the kd greater the affinity