Urinary Calculi

Prostate Cancer Urinary Calculi Vitamin C Supplementation and Urinary Oxalate Excretion Reviewed by Dean G. Assimos, MD Department of Urology, Wake Forest University School of Medicine, Winston-Salem, NC [Rev Urol. 2004;6(3):167] © 2004 MedReviews, LLC rinary oxalate excretion plays a critical role in calcium oxalate stone formation. The majority of urinary oxalate is derived from endogenous synthesis and dietary sources. There has been an ongoing debate regarding the impact of vitamin C supplementation on urinary oxalate excretion. The 2 articles discussed here provide further information on this subject. U Effect of Vitamin C Supplements on Urinary Oxalate and pH in Calcium Stone-Forming Patients Baxmann AC, De O G Mendonca C, Heilberg IP. Kidney Int. 2003;63:1066-1071. Adult calcium oxalate stone–formers were administered either 1 gram (group 1) or 2 grams (group 2) of vitamin C daily for 3 days while healthy, non–stone-forming adults (group 3) were given the 1-gram dose daily during the same time. The participants were not placed on a metabolic diet, but were instructed to refrain from consuming foods rich in vitamin C and oxalate, as well as dairy products. Twentyfour-hour urine collections were obtained at baseline and after vitamin C administration. Urinary pH did not change after vitamin C supplementation in any of the groups. However, there were statistically significant increases in oxalate excretion in all 3 groups: 61% in group 1, 41% in group 2, and 56% in group 3. A significant increase in calcium oxalate urinary supersaturation (by Tiselius index) occurred in all groups after supplemental vitamin C intake. Effect of Ascorbic Acid Consumption on Urinary Stone Risk Factors Traxer O, Huet B, Poindexter J, et al. J Urol. 2003;170:397-401. In this double-blind, randomized, crossover study, adult calcium oxalate stone–formers and non–stone-forming adults were placed on a controlled metabolic diet for 2 6-day phases. During one of the phases, they were given 1 gram of vitamin C twice a day, and they received a placebo during the other phase. Twenty-four-hour urine specimens were collected on days 5 and 6 of each phase. Vitamin C supplementation should not be used in managing patients with struvite calculi, because it does not reduce urinary pH, or in calcium oxalate stone–formers, as it might promote stone activity. There were no changes in urinary pH after vitamin C ingestion in either group, although there was a moderate and statistically significant increase in urinary oxalate excretion in controls (20%) and stone-formers (33%). Conclusions Both of these articles clearly demonstrate that 1 to 2 grams of ascorbic acid administered daily to both normal subjects and calcium oxalate stone–formers result in no urinary pH changes but in increased oxalate excretion. Therefore, this practice should not be used in managing patients with struvite calculi, because it does not reduce urinary pH, or in calcium oxalate stone–formers, as it might promote stone activity. Prostate Cancer Prostate Cancer and Chemotherapy Reviewed by Masood A. Khan, MD, Alan W. Partin, MD, PhD Department of Urology, Johns Hopkins School of Medicine, Baltimore, MD [Rev Urol. 2004;6(3):167-169] © 2004 MedReviews, LLC espite the increase in the number of patients presenting today with clinically localized prostate cancer who undergo definitive local therapy (either radiation therapy or radical prostatectomy), approximately 50% will experience advanced disease recurrence.1,2 In these patients or patients presenting initially with advanced disease, suppression of androgenic activity with either surgi- D VOL. 6 NO. 3 2004 REVIEWS IN UROLOGY 167