Ex. 2 L3: Multicompartmental analysis Flashcards
Multicompartment:
Drug given as IV bolus; 2 compartment Pk model, curve presents as small slope in beginning, then linear after
2-compartment PK model aka…
Bi-phasic; Initial rapid concentration drop first, followed by slower pK phase
One compartment model
The body acts like a single homogenous compartment and drug rapidly distributes uniformly in it
The drug is in rapid equilibrium between the blood and the tissues
Changes in the plasma conc. of drug will result in proportional changes in tissue drug levels
One (i.e. blood) compartment alone is sufficient enough to explain drug disposition
Multi-compartment model
Bi-phasic pK
After admin, drug is distributed to different compartments, leading to bi-phasic pK (rapid concentration drop)
Drug goes to fat first
Slower pK later because drugs that went to fat first come back to stream later for elimination
Multi compartment distribution
Liver -25% of cardiac output
Follow pretty much the same pattern as drug concentration in plasma
Liver and plasma parallel to each other
Drug distribution: central compartment
Kidney, liver blood
Drug distribution:
peripheral tissues
Fats
Peripheral organ
Why are two compartments needed?
Distribution into fat (lipids) Determines what happens in the central compartment (blood, kidney, liver)
Why multi-compartment model is used
One (i.e. blood) compartment alone is not sufficient to explain drug disposition. More than one (i.e. multi) compartments are needed
-Goes different places
Ex.:
Blood: T1 100ng/ml
Tissue: T1 10ng/ml
Blood: T2: 50ng/mL
Tissue: T2: 7ng/ml - not proportional, need explanation for where the rest went
See a CURVE, not a straight line
One compartment vs two compartment model summary
One: C = C0 * e^-kt
Linear
Two compartment:
C= Ae^-at + Be-^Bt
Slight curve turns to linear
Distribution phase
1st of two biphasics
Elimination also occurs, but distribution into the tissues compartment governs the slope
Elimination phase
2nd biphasic
Elimination from the central compartment governs the slope
Bi-phasic pk explained
Drug amount in tissue increases over time until it hits max; once it reaches max, drug in tissue/peripheral compartment Comes back for elimination
Why does drug have to come back to central compartment for elimination?
The major drug eliminating organs, liver, kidney, blood, are part of central compartment
T/F: Compartment models are a drug specific property
True
