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Body Compartment Model

Volume of Distribution is considered in relation to body “compartments”.

Some highly polar drugs, such as penicillins, distribute mainly into “central” compartments and have a small Vd, while highly lipid soluble drugs, such as tricyclic antidepressants, distribute far more widely and have a large Vd.

Inject drug, and progressively add compartments to see what happens as the drug distributes more widely in the body.

You will see that Ab (Amount in body), Vd and Cp are clearly related.

STEP 1

Inject

STEP 2

Add ECF

STEP 3

Add ICF

STEP 4

Add Muscle

STEP 5

Add Fat

RELOAD

Reload

dose(Ab)= 100 mg

dose(Cp)= 20 mg/L

vol(Vd)= 5 L

Plasma 5L

ECF 10L

Extra Cellular Fluid

ICF 30L

Intra Cellular Fluid

Muscle 100L

Fat 1000L

Amount in body = Vd x plasma concentration

Ab = Vd x Cp

Vd = Ab