True or false: Loading dose equals Css,inf times Vd.

True or false: Loading dose equals Css,inf times Vd.

• A. False; Loading dose equals Css,inf times Vd
• B. True; Loading dose equals Css,inf times Vd
• C. False; Loading dose equals Css,inf divided by Vd
• D. False; Loading dose equals Css,inf divided by Cl

Answer: (B)

Loading dose is used to quickly reach the target steady-state concentration by delivering an amount that, when distributed in the body, yields that concentration. For an IV bolus, right after the dose the concentration is D/Vd. To hit the desired Css,inf, set D/Vd = Css,inf, which gives D = Css,inf × Vd. That’s why the loading dose equals Css,inf times Vd. In linear pharmacokinetics, a maintenance rate would then be Css,inf × Cl to keep the concentration at Css,inf. If distribution isn’t instantaneous or kinetics are nonlinear, adjustments are needed, but under standard assumptions this relationship holds.

Loading dose is used to quickly reach the target steady-state concentration by delivering an amount that, when distributed in the body, yields that concentration. For an IV bolus, right after the dose the concentration is D/Vd. To hit the desired Css,inf, set D/Vd = Css,inf, which gives D = Css,inf × Vd. That’s why the loading dose equals Css,inf times Vd. In linear pharmacokinetics, a maintenance rate would then be Css,inf × Cl to keep the concentration at Css,inf. If distribution isn’t instantaneous or kinetics are nonlinear, adjustments are needed, but under standard assumptions this relationship holds.