A LITTLE LIGHTBULB MOMENT
Pharmacokinetics and pharmacodynamics · Applied pharmacokinetics
Half-life from clearance and distribution
Sign in to bookmark this concept and add private notes →
Bigger space slows the half; bigger clearance speeds it.
The idea behind the cue
For first-order elimination, half-life = ln(2) × Vd/CL.
Practice this flashcard →Make it memorable
Short & simple
Bigger space slows the half; bigger clearance speeds it.
Acronym
Bigger space slows the half; bigger clearance speeds it.
Story
Bigger space slows the half; bigger clearance speeds it.
Connect the pieces
- 0.693 × 40/5 = 5.544 hours; one decimal = 5.5 hours.
Know the limits
Original educational exercise. Use only the stated assumptions; a calculated quantity is not a prescribing recommendation. Real dosing requires drug-, indication- and patient-specific guidance.
Merck Manual Professional · Overview of Pharmacokinetics ↗Check your understanding
A linear one-compartment drug has Vd 40 L and clearance 5 L/hour. Calculate half-life to one decimal hour using ln(2) = 0.693. Enter the number only.
Reveal explanation
5.5 hours (tolerance ±0.05)
0.693 × 40/5 = 5.544 hours; one decimal = 5.5 hours.
Merck Manual Professional · Overview of Pharmacokinetics ↗