Your prescription tooth paste probably is heavy on fluoride to either prevent new cavities or help with sensitivity. MI paste helps recalcify your enamel. Depending on what your prescription toothpaste is needed for, you can use it either at night before you go to bed and before you whiten or in the am after you whiten.
We have found that using a toothpaste with Potassium Nitrate helps sensitivity when whitening. In that instance, we tell you to put the toothpaste in your whitening trays and wear them for a half hour before whitening, whiten and then you can use toothpaste in the trays after to help if you are really sensitive.
Hope that helps-Keep up the good job!