Diane this is a huge dose. I would ask for a stronger antacid like a proton pump inhibitor PPI. Please be careful too how he comes down from such a high dose, my son was on 60 mgs once after surgery for inflammation purposes.  It also affected his stomach terribly and caused him so much pain, despite taking it with food. How long do they want your son on this for? My son felt terrible on it.  PLease let us know how he gets on. I would make the endo aware of this, I am shocked at the dose.  Good luck. Mary