Hi, Gastric ulcers can be difficult to treat and often require a prolonged course of medication to heal. Commonly they are caused by an actual bacterial infection called H. pylori, and treating this involves a regimen of antibiotics. The Pantoprazole likely decreased the acid in the stomach and allowed at least a partial blood clot to form over the ulcer. My suspicion, and please understand this is somewhat of speculation, is that the blood clot was dislodged and the gastric ulcer began to re-bleed. Since we know he already was anemic and required 2 units of blood in the hospital, I would recommend that you take him back to the emergency room. This is the safest course of action and his blood count can be rechecked. Other concerns are that he make another source of bleeding beyond the stomach ulcers that were not address initially, however regardless of this he does need re-evaluated as soon as possible. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. David Girardi, Internal Medicine Specialist