In past investigations and suits over reverse-payment settlements, the FTC has not challenged the validity of the underlying patent infringement litigation. The FTC's argument lays out a detailed explication of the patent environment and history, focusing on an ingredient in branded AndroGel called isopropyl myristate (or IPM), which is known as a "penetration enhancer" because it speeds the delivery of the drug's active ingredient, testosterone, through the skin and into the bloodstream. Although Teva and Perrigo developed testosterone gel products that did not contain IPM and used different penetration enhancers than AndroGel, the Abbott Defendants sued Teva and Perrigo for patent infringement. The Abbott Defendants therefore allegedly used the statutory 30-month litigation stay merely as a tactic to delay introduction of generic AndroGel.