How long should I use Colgate PreviDent 5000 Booster Plus toothpaste for?

Using these two together is not a problem, and can be used indefinitely. Calcium and vitamin tabs should not be an issue.

I instruct patients to do exactly what you are doing.  regular toothpaste in the morning and then Prevident at night.  Make sure not to drink anything after brushing as it can wash away the residual fluoride and diminish the effect.  You are not swallowing the toothpaste so there is really no systemic effect, only a localized coating on the teeth.  This should not interfere with any other medications or supplements.