Table 1:

Key Definitions

Potency	The amount of drug required to produce a specified effect. A highly potent drug is active at low concentrations. Classically quantified as the required concentration to achieve half the maximal effect (EC50).
Efficacy	The degree to which a drug can produce a beneficial effect. Classically quantified as the maximal effect (Emax).
Synergistic Potency	The magnitude of the change in the drug potency, due to the presence of another drug.
Synergistic Efficacy	The percent change in the maximal efficacy of the combination compared to the most efficacious single agent.