When my son’s 17ohp was out of wack it took us putting him on a really high dose for a short time (I think it was three weeks) to bring the 17ohp down.  Then, after lab  work,  we were able to decrease his dose in less than half for maintenance.  You may want to ask your endo. about this. 

It may help while you are trying to lower the 17ohp to also split the dose into 4x/day to really stay on top of the 17ohp. 

Best wishes to you and your son.

Lisa