In a semi-log plot, if the line is steep, what does that indicate about elimination rate?

In a semi-log plot, if the line is steep, what does that indicate about elimination rate?

• A. Higher Volume of Distribution
• B. Lower Clearance
• C. Higher Elimination Rate
• D. Longer Half-life

Answer: (C)

A steep line on a semi-log plot means the elimination rate constant is large. In first-order elimination, concentration versus time on a log scale is a straight line with slope equal to -k, where k is the elimination rate constant (the fraction of drug eliminated per unit time). A larger magnitude of the slope indicates a larger k, so the drug is being eliminated more quickly per unit time. That’s why a steeper line corresponds to a higher elimination rate. Keep in mind that a larger k also shortens the half-life (t1/2 = 0.693/k).

A steep line on a semi-log plot means the elimination rate constant is large. In first-order elimination, concentration versus time on a log scale is a straight line with slope equal to -k, where k is the elimination rate constant (the fraction of drug eliminated per unit time). A larger magnitude of the slope indicates a larger k, so the drug is being eliminated more quickly per unit time. That’s why a steeper line corresponds to a higher elimination rate. Keep in mind that a larger k also shortens the half-life (t1/2 = 0.693/k).