Choose the correct ending to this sentence below and explain why? Many drugs are competitive inhibitors of specific enzymes. In such cases........
A. the amount of drug needed to achieve the same effect is increased as the substrate concentration increases.
B. the amount of drug needed to achieve the same effect is increased as the substrate concentration decreases.
C. substrate must be bound to the enzyme before the drug can bind.
D. the enzymes have to be allosterically regulated.

Competitive inhibition is when identical molecules to the substrate molecules gets bonded to the active site which then hinders the binding of the actual substrate. An example of competitive inhibitor is penicillin, since it blocks an enzymes active site which us used in the construction of the bacteria cell.

Then, the correct statement will be:

"Many drugs are competitive inhibitors of specific enzymes. In such cases, then the amount of drug that'll be needed to achieve the same effect is increased when the substrate concentration increases".

Therefore, the correct option is A.