Complex sentence: Antacid preparations such as cimetidine suppress the acid-mediated break down of proteins, leading to an elevated risk of developing food or drug allergies due to undigested proteins passing into the gastrointestinal tract where sensitisation occurs.
Split into simpler sentences: Antacid preparations such as cimetidine work by suppressing acid mediated break down of proteins, leads to an elevated risk of developing food or drug allergies. This happens due to undigested proteins then passing into the gastrointestinal tract where sensitisation occurs.