Clearance

Total volume of plasma from which drug is completely removed per unit of time (units = ml/min).  May be viewed as a proportionality constant that relates the rate of elimination to C_p.  

Rate of Elimination = Cl C_p         (1)

Rate of Elimination = (dq_T/dt) = q_Tk_e     (2)

Cl C_p = q_Tk_e                            (3)

Cl = (q_Tk_e)/C_p = V_dk_e                    (4)

Cl = Dose/AUC      

(AUC is area under plasma concentration vs. time curve )

	Drug
Variable	A	B
Clearance, ml/min	1500	100
Rate of elimination, µg/min	15	500
Volume of distribution, liter	20	0.7
Plasma concentration, mg/liter	0.01	5

This table shows that a rapidly cleared drug (A) can be eliminated slowly if the C_p is low.  Drug B is rapidly eliminated even though the clearance is low because the V_d is small and the C_p correspondingly high.

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B.7c-1