The P5P form is what is used in cellular reactions, and 70-90% of the vitamin B6 circulating in plasma is this active form.[ref] The first step of the B6 conversion process in the liver involves pyridoxal kinase ( PDKX gene)
PMID 29733881
Pickart, L., Vasquez-Soltero, J., Pickart, F., & Majnarich, J
There are reports of rare cases of toxicity following dosing within the therapeutic range, although there is debate about whether this latter category truly exists
It really depends on your lifestyle, diet, and how active you are
In a study published in 2017, the long-term use of metformin (Glucophage), an anti-diabetic medication, was correlated with a lower risk of gallstones in diabetic subjects (Liao 2017)