One compartment model

Assumptions:

• Once in the circulation, the drug distributes instantaneously through out the body
• Absorption and elimination follow first order kinetics.  (Amount eliminated in a fixed duration of time is directly proportional to the amount of drug in the body)

First order

What changes?

What stays constant?

Changes: Rate of elimination with dose

constant: K_el and t_1/2

VD

5

10-20

40

40-60

• 5: Blood
• 10-20: Blood + ECF
• 40: All body water
• 40-60: In tissue

binds acidic and neutral

50% of plasma proteins

50% in extracellular compartment

multiple binding sites with varying affinity

Binds basic and neutrals

one high affinity site

Elevated levels seen with trauma

Metabolism by liver

excretion by kidney

Skin & GI also can metabolize

Excretion in bile, or by lungs