Drug(1) "is not" Drug(2)

What does we mean when we say that two things "are the same"?

In the multibillion-dollar pharmaceutical industry, the company that owns the patent makes the bucks. But patents don't last forever and when they expire, other companies acquire the right to make "generic" copies of the drug to sell in competition with the patent holder. To get approved, generics manufacturers mostly need to show that their drugs "are the same as" the original patented chemical--the same chemical structure implies the same efficacy and safety. That's how the drug industry works.

As with so many other standard practices of industry today, this may soon change, with billions hanging in the balance. A new class of drugs, known as biopharmaceuticals will soon reach the end of their patent protection, when competitors can start making generic alternatives. A regulatory discussion has erupted around these "biogenerics" concerning the issue of "same"-ness.

As this article in the Minneapolis-St. Paul Star Tribune reports, the biopharmaceutical process starts with an individual living cell's genetic material and ends with a flotilla of clone cells pumping out the target molecule under extremely controlled conditions. The generic process necessarily varies from the original at the very start, since they cannot begin with same first cell.

So drug(1) is not drug(2). Does it matter? How much "samenss" can we expect (knowing that we can never call two things "identical"), and how much difference can we tolerate before determining that the generic might not perform like the original?