#3623 Lanthanum carbonate does not reduce urinary oxalate excretion in hyperoxaluric kidney stone formers

BACKGROUND AND HYPOTHESIS: Hyperoxaluria is an important risk factor for kidney stone formation. Currently available treatment options for idiopathic hyperoxaluria have limited efficacy and are difficult to maintain in the long-term. Pre-clinical data suggested that Lanthanum Carbonate (LaCa) might efficiently bind oxalate. In this multicenter, open-label, dose-response study we assessed the efficacy and safety of LaCa in the reduction of urinary oxalate excretion in stone formers with idiopathic hyperoxaluria. METHODS: Stone formers with urinary oxalate excretion > 45 mg/24h were treated with LaCa at a dose of 750 mg daily during a first 14-day treatment period, followed by a second 14-day treatment period with 1500 mg LaCa daily. The study was powered for the primary efficacy endpoint of detecting a ≥20% urinary oxalate excretion reduction after the first treatment period (AFTP). Secondary endpoints were the incremental reduction of urinary oxalate excretion with LaCa dose increase to 1500 mg during the second treatment period (ASTP) and the effect on serum phosphate and urinary phosphate excretion. RESULTS: Forty-four patients started the study, 42 completed the two months follow-up. LaCa treatment with both the 750 and 1500 mg dose had no effect on urinary oxalate excretion (52.0 mg/24h at baseline [BL], 49.1 mg/24h AFTP [p=0.25], 52.6 mg/24h ASTP [p=0.01 compared to AFTP, p=0.86 compared to BL]). Urinary phosphate/creatinine ratio and fractional excretion (FE) of phosphate decreased significantly after treatment with 1500 mg LaCa (17.1 mmol/g at BL, 15.2 mmol/g ASTP, p=0.003 for urinary phosphate/creatinine ratio and 16.6% at BL, 14.7% ASTP, p=0.002 for FE phosphate), while LaCa had no effect on serum phosphate (0.97 mmol/L at BL, 0.95 mmol/L ASTP, p=0.29). CONCLUSION: Short-term treatment with LaCa at doses up to 1500 mg did not reduce urinary oxalate excretion in stone formers with idiopathic hyperoxaluria. Urinary phosphate excretion decreased without effect on serum phosphate.