Here's the critical text of the law, with a confusing parenthetical omitted:
It shall not be an act of infringement to make, use, or to sell, or sell within the United States or import into the United States a patented invention ... solely for uses reasonably related to the development and submission of information under a Federal law which regulates the manufacture, use, or sale of drugs or veterinary biological products.
So one reading of this law is that Amphastar (or Teva) could freely infringe on MNTA's patent during the development process just so long as they don't infringe during the manufacturing process. I personally think that reading of the statute goes beyond the intent of the law, but it is still an argument that MNTA will have to deal with.