GasGasGas - The FRCA Primary Exam Podcast Gas Gas Gas - Poly-Compartmental Madness - Half time, Tc, Natural Log and more
Jan 8, 2025
Explore the fascinating world of multi-compartmental pharmacokinetics! Discover the importance of half-lives, time constants, and how they impact drug clearance and offset times. Learn how to visualize time constants and relate them to elimination rates. Dive into the role of natural logarithms in modeling kinetics and unravel the mysteries of bi-exponential decay on concentration-time graphs. Prepare for a future demonstration using these concepts with a fentanyl patient model! Perfect for aspiring anesthesia professionals.
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Half-Life Depends On Distribution And Clearance
- Half-life describes time for a substance to halve and applies to plasma drug concentration as an exponential decay.
- Volume of distribution and clearance determine how much drug is available in plasma and thus affect half-life.
Time Constant Links To Half-Life
- Time constant (tau) is the extrapolated time from the initial slope to the x-axis and links to half-life exponentially.
- Half-life = 0.693 × time constant, because ln(2)=0.693 in natural logs.
k Connects Slope, Vd And Clearance
- The elimination rate constant k is the inverse of the time constant and describes the initial slope gradient.
- Clearance = volume of distribution × k, tying Vd, k and clearance together mathematically.