Can I use Katsuo Stamina for ultra-marathons or Ironman-distance events?

Yes. Katsuo Stamina has dosing guidance for long events, including ultra-marathons and other endurance sports. For ultras, the current schedule is 8 tablets before the start, then 4 every 120 minutes. It should be used alongside your normal carbohydrate, fluid and electrolyte strategy rather than replacing it.