Factors affecting the plasma
conc-time profile (Cont'd)

c- Km

Examine the conc-time profiles after administration of the same dose when Km is different.

Parameters
Dose (mg) Vmax (mg/hr) Km(mg/L)
500 30 20
Km (mg/L)
Notice that when the conc is
much higher than Km the rate of
drug elimination is approximately
similar (approximately equal to
Vmax)
Parameters
Dose (mg) Vmax (mg/hr) Km(mg/L)
500 30 20
Km (mg/L)
Large difference in the rate of
drug elimination is observed
when the drug conc is in the
range of Km

Smaller Km results in higher total body clearance, and shorter half life which leads to faster rate of drug elimination and smaller AUC.

Parameters
Dose (mg) Vmax (mg/hr) Km(mg/L)
200 40 20
Km (mg/L)

Smaller Km results in higher total body clearance and faster rate of drug elimination. After multiple administration of similar doses, the steady state conc will be lower when Km is smaller.

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