|I agree with Karen. PPIs like Prevacid or Zegerid (or Prilosec or Nexium...) are considered the gold standard in treating reflux because they actually stop the acid production from happening in the first place. H2 blockers (like Zantac) merely work to "neutralize" the acid once it's already there - and the body can quickly build up a tolerance to H2 blockers and they will stop working. Please do go to Marci-kids.com and read everything you can to learn more about the different classes of drugs and how they work.
I also agree that Enfamil AR is not the answer. Thickened liquids may "stay down" better - but it's not the act of spitting up that is causing him pain (which you know, now that he's stopped spitting up but is still having pain). It's the acid IN the spit up - and the acid burning his esophagus even when he doesn't actually spit up - that is causing the pain. You need to address the acid. Until that is under control the Enfamil AR will not help.
If he's still suffering once he's on a PPI (make sure it's an appropriate dose and that you're administering it correctly either on an empty stomach 1 hr. before a meal - or by using Buffer Babies or Caracream from Marci Kids), please look into the possibility of MSPI (milk soy protein intolerance). It's not an uncommon problem in infants less than a year old. Often reflux and MSPI go hand-in-hand...and it's difficult to tell which one you're dealing with, or if you're dealing with both, because the symptoms mimick each other.
To rule a protein intolerance in or out, you'll have to do a trial of Enfamil Nutramigen or Similac Alimentum formula. The proteins in these formulas are partially broken down so as not to cause digestive upset/reactions. If your son is particularly sensitive, he may even need Neocate or Elecare - specialty formulas in which the proteins are COMPLETELY broken down. These formulas are basically guaranteed not to cause reactions. To learn more visit Neocate.com and read everything under the Parents tab.
Keep us posted on his progress. Hope you can get him feeling better soon!