The primal defense is a probiotic, and Threelac is designed to kill probiotics - only certain ones they say, but who knows? It could be going after all of them. So you might want to only take the primal defense when you're not taking Threelac - they might cancel each other out.
Once you're done with a rotation, then take it. And when you're done with an entire 2 weeks rotation, mega-dose the primal defense for a couple weeks. After that you should only need maintenance doses unless you do more Threelac.
It helps to learn muscle testing - have your partner do the arm press type while holding PD and see if you need more, after the megadosing. :)