Apparent Volume of Distribution

Relates total amount of drug in body to the concentration of drug in PLASMA.

q_T = V_d(C_p)

Units of V_d = ml, liter, liter/kg body weight

V_d = Dose/C_o = Dose/[AUC(k_e)]

where AUC is area under the curve of the plasma concentration versus time curve

V_d - does not correspond to any anatomical space

High V_d (e.g 20 liters/kg) - present in high concentration in tissue relative to plasma.

Low V_d (e.g. 0.1 liters/kg) - present in high concentration in plasma relative to other tissues.

Volume of plasma in a 70 kg male is approximately 2 liters.

Drug Type	Vd
Binds to plasma proteins	Plasma volume (0.05 liters/kg)
Not highly bound to plasma but don't enter cell	Total extracellular water volume (0.2 liters/kg)
Enter cells freely	Total body water volume (0.55 liters/kg)
Binds to tissues	Extremely high Vd's >10 liters/kg

---

B.8