Oral drug administration

The rate of drug absorption significantly affects the plasma conc-time profile after a single oral dose when drug elimination is nonlinear.

ka (hr -1)
Dose = 1000 mg
Vd = 25 L
Km = 5 mg/L
Vmax = 40 mg/hr

After administration of the same dose of a drug, rapidly absorbed formulations achieves higher and prolonged conc (larger AUC) compared to slowly absorbed formulations.

This is because faster drug absorption produces higher maximum plasma conc of the drug. At higher plasma conc the total body clearance is lower and the half life is longer when drug elimination is saturable.

The steady state conc is dependent on the dose, Vmax and Km. So, the rate of absorption does not affect the average steady steady state. However faster absorption leads to larger fluctuations in the plasma conc.

ka (hr -1)
Dose = 300 mg
Vd = 15 L
Km = 10 mg/L
Vmax = 45 mg/hr
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