what is the IMPORTANCE of renal drug excretion?

Answer 1

If you don't get rid of it - it circulates in your body FOREVER! Renal drug excretion is the primary mode of elimination of most medications.

In some cases, the medications are cleared directly by the kidney (particularly if they are water soluable).

In other cases, they have to be metabolized by the liver to change them into a water soluable form.