The overall negative effect of colas on our bodies makes it no surprise that one should avoid colas if they have weak kidneys. Colas have an enormous amount of phosphorus and potassium in them. This is not natural, these substances are added into the colas artificially, making them even less suitable for human health.
The artificial additives may not fully be filtered out by the kidneys, damaging the intestinal tract and some other organs in the long run. We cannot know the exact amount of these substances as manufacturers are not forced to mention the quantity in their ingredient lists.