I think they do know that its impossible to test all the interactions, Since this is such a high number, but that points out the crazyness of using chemicals as a quick fix to solve every problem for profit.
Imagine how much that number would be reduced, if we eliminated all of the needless drugs that are quickfixes for problems that can be solved with common sense, diet, excercise, herbs etc, leaving only the drugs that actually save lifes in emergency medicine, where benfeits outweigh the risks.
The number of interactions to test for would be more feasible!
It highlights the need for longer clinical trials instead of getting the drugs on the market as soon as possible and using the general public as the test subjects.