GasGasGas - The FRCA Primary Exam Podcast Gas Gas Gas - Poly-Compart-Mental Madness Part Two - Ft. Pharmacokinetic BathTubs.
Jan 21, 2025
Dive into the intriguing world of pharmacokinetics! Discover why single-compartment models can mislead and how multi-compartment thinking enhances clinical practice. Learn about the fascinating impacts of infusion rates on drug concentration using relatable alcohol analogies. Explore the role of molecular weight and solubility in drug movement and how medications like fentanyl behave during prolonged infusions. Plus, enjoy a quirky bathtub analogy that illustrates complex drug distribution dynamics!
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Compartment Models Explain Drug Distribution
- Multi-compartment models use a central (plasma) compartment plus well- and poorly-perfused compartments and sometimes an effect-site compartment.
- These theoretical compartments approximate tissue groups and explain why single-compartment kinetics can be misleading.
The 'Caspian Adiposity' Fentanyl Metaphor
- James uses a hyperbolic 'Caspian adiposity' metaphor to show a huge lipid sink filling with fentanyl over prolonged infusion.
- He describes stepwise saturation of compartments requiring progressive reductions in infusion to maintain plasma steady state.
Saturation Lowers Infusion Requirements
- As peripheral compartments saturate, the infusion rate needed to maintain a given plasma concentration falls until it equals hepatic/renal clearance.
- At full equilibration concentrations across compartments become similar despite differing compartment volumes.