Which statement about MEC and therapeutic response is true?

• A. MEC marks the exact point of maximum therapeutic effect.
• B. MEC is the beginning of the therapeutic response; the peak from MEC determines the maximum effect.
• C. The intensity of the response is proportional to the plasma concentration.
• D. Therapeutic response occurs only after the drug is fully eliminated.

Answer: (C)

The key idea is how the drug’s effect relates to its concentration in the blood. MEC, or the minimum effective concentration, is the lowest plasma level at which a therapeutic effect becomes detectable. It marks the threshold for effect, not the point of maximum effect.

As the plasma concentration rises, the amount of drug available to engage targets increases, so the intensity of the response tends to rise as well. In the common, simple view of the dose–response relationship, the response is roughly proportional to concentration within the therapeutic range: more drug in the system often means a stronger effect, up to a limit where receptors become saturated and the effect plateaus at its maximum (Emax). That makes the statement about proportionality the best fit among the choices.

The other ideas don’t fit: MEC does not indicate the maximum effect, and the peak effect is governed by factors like Emax and EC50, not simply by the MEC. Also, a therapeutic response begins while the drug is present in the body, well before elimination is complete.