Mean Dissolution Time (MDT) is defined as which of the following?

• A. MDT is derived from in vivo pharmacokinetic data.
• B. MDT is derived from in vitro dissolution profiles.
• C. MDT is derived from stability data.
• D. MDT is derived from solid-state characterization.

Answer: (B)

Mean dissolution time reflects the average time needed for the drug to dissolve, based on dissolution data collected in vitro. It condenses the dissolution profile into a single metric that describes how quickly the drug releases from a solid form under the test conditions. Conceptually, you derive it from the dissolution curve by integrating the fraction dissolved over time and dividing by the total amount that can dissolve: MDT = ∫0^t M(t) dt / M∞, or in discrete form MDT = Σ t_i ΔM_i / M∞, where ΔM_i is the amount dissolved in each interval and M∞ is the total dissolved amount. This makes MDT inherently an in vitro measure of dissolution rate, useful for comparing formulations or process changes. It is not derived from in vivo pharmacokinetic data, stability data, or solid-state characterization, which relate to absorption and metabolism, shelf-life/degradation, and crystal form, respectively.