Pharmacotherapy and Stone Mineral Subtype Influence Long-term Recurrence Rates in Calcium Stone Formers.

Background: Long-term recurrence data on kidney stones is limited. We investigated stone recurrence in calcium-oxalate (CaOx) and calcium-phosphate (CaP) stone formers over a 10-12-year follow-up period.

Methods: We retrospectively identified patients from a surgical database with 1)CaOx or CaP stones, 2)post-surgical computed tomography imaging, and 3)at-least 10 years of clinical follow-up and imaging. Data on medical therapy (MT), defined as being on thiazide/thiazide-like diuretic, potassium citrate, and/or allopurinol, was collected. Patients' records were reviewed for stone recurrence over a 10-12-year period. Associations between stone type, medical therapy, and time to recurrence were analyzed with Kaplan-Meier survival curves and Cox proportional hazard models. Multivariate analysis was done using Cox proportional hazard model.

Results: Of the 149 individuals who met inclusion criteria, 87 (58.3%) underwent baseline 24-hour urine testing, and 46 (30.8%) were prescribed MT in the form of thiazide (26/46; 57%), potassium citrate (25/46; 54%), allopurinol (5/46; 11%). Compared to non-MT, patients on MT were more likely to have diagnosis of hypertension(p=0.008) and be hypocitraturic at baseline(p=0.01). Over a mean of 10.6 years, patients on MT had significantly fewer stone events compared to those not on MT(21.3% vs 37.5%, p=0.04) with 8(17%) individuals discontinuing their MT over the study period. Patients with predominantly CaP mineral subtype had more stone events than CaOx (64% vs 36%, p=0.006), a phenomenon likely driven by higher baseline urine pH (>6,58.8% vs 33.9%, p=0.02). By survival analysis, the impact of stone subtype and MT became apparent at follow-up month 20 and 60, respectively.

Conclusions: In a population of calcium stone formers at high recurrence risk, patients with CaOx mineral subtype and on MT had the lowest stone event rate on long-term follow-up. These findings suggest that the beneficial effect of medical therapy may take up to 5 years to become evident clinically and by surveillance imaging.