By Catherine Fredenburgh (April 21, 2006, 12:00 AM EDT) -- In the latest development relating to the triggering of the 180-day generic marketing exclusivity period, the U.S. District Court for the District of Columbia upheld the Food & Drug Administration's ("FDA") April 11, 2006 letter ruling, in which FDA adopted a new "holding on the merits" test. In its letter ruling, FDA determined that only a decision on the merits holding the brand company's patent invalid, unenforceable or not infringed, will trigger the running of the 180-day generic exclusivity period. FDA rejected the argument that a dismissal of a declaratory judgment action relating to the patent triggers the running of the exclusivity period. On April 19, the D.C. District Court upheld FDA's decision, finding FDA's approach to be permissible under the statute. Pharmaceutical companies and their counsel will need to stay tuned, however, because the U.S. Court of Appeals for the D.C. Circuit will ultimately decide this important issue....