How does distal RTA cause kidney stones?
In distal RTA, stone formation is common, and most stones are calcium phosphate.
The systemic metabolic acidosis leads to increased proximal tubule reabsorption of citrate, lowering urine citrate excretion. Because there is less citrate available to complex calcium, there is more calcium available to combine with phosphate or oxalate.
Acidosis increases renal calcium excretion, further increasing the risk of stones. Finally, the inability to acidify urine leads to a persistent alkaline urine, which increases the amount of divalent phosphate (pK = 6.8) and thus the risk of calcium phosphate crystallization.
Carbonic anhydrase inhibitors, such as topiramate and acetazolamide, can cause kidney stones by creating an RTA.