My GFR was 57 a month ago, varies between 50 and 60 for the last ten years and doctors are not concerned. Just say avoid anti-inflammatories. Fine. Now I have really bad chest pain which doc says is osophagitis and has given me a huge bottle of Gaviscon Advance. Clearly says not to be taken by people with kidney problems Because it contains potassium. So haven't taken any - don't know bad kidney probs have to be before you shouldn't take it.