After adding Drug A to an enzyme - substate reaction, Km remains same and Vmax decreases.
 Drug A is a: (A) Competitive antagonist, (B) Non competitive antagonist, (C) Agonist, (D) None of the above
Answer is B. In Non competitive Antagonism: Km remains same, Vmax decreases.
In Competitive Antagonism: Km increases, Vmax remains same.