Onset of action is defined as the time to reach MEC.

Onset of action is defined as the time to reach MEC.

• A. Time above MEC
• B. Time to reach MEC
• C. Time to reach Cmax
• D. Time to drop below MEC

Answer: (B)

Onset of action is the time it takes for the drug concentration to reach the minimum effective concentration. This threshold is the point at which the pharmacologic effect begins, so onset is defined by the duration from dosing to crossing MEC. The time the concentration stays above MEC describes how long the drug remains active (duration of action), not when it first starts. Reaching Cmax occurs later and relates to peak concentration rather than the initial onset. The time to drop below MEC marks the end of the effect (offset).

Onset of action is the time it takes for the drug concentration to reach the minimum effective concentration. This threshold is the point at which the pharmacologic effect begins, so onset is defined by the duration from dosing to crossing MEC. The time the concentration stays above MEC describes how long the drug remains active (duration of action), not when it first starts. Reaching Cmax occurs later and relates to peak concentration rather than the initial onset. The time to drop below MEC marks the end of the effect (offset).