Urinary Stone Inhibitors

It is intriguing that despite marked abnormal urinary factors, most humans will not form stones. Alternatively, some patients develop stones despite normal urinary composition. The key element, therefore, appears to be inhibition of the steps in calculogenesis (nucleation, crystal growth, aggregation, and crystal/stone retention). Urolithiasis will not develop if any one of these steps is blocked. Despite this simple fact, it is unclear exactly why many people form stones. Numerous molecules have been identified that inhibit crystallization in vitro but many stone formers have normal levels of these substances; others will continue to develop stones despite replacement of these known inhibitors. The formation of urinary calculi requires a complex combination of factors, both promoting and inhibiting stone formation. Fortunately, there are many patients who can be helped because of our existing knowledge about two specific urinary inhibitors: citrate and magnesium. This chapter will discuss the in vitro and in vivo evidence regarding citrate and magnesium as inhibitors of urinary stone disease.