This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General Pharmacology, Subject name: Pharmacology
In the given pharmacodynamic curve, point A corresponds to: 
Select and explain. 
A. Potency, B. Efficacy, C. ED50, D. LD50
C: ED50
Answer: C: ED50 
Explanation: Ans. (C) ED50 Quantal DRC is employed for conditions where there is all or none response. It is used to calculate median effective dose (ED50 ) and median lethal dose (LD50 ). ED50 is the dose at which 50 percent of the recipient gets the desired (or undesired) action. It is calculated from the quantal DRC as shown in the figure. The same point in graded DRC corresponds to potency of the drug.