Abstract
Background: Vitamin C can be metabolized to oxalate. Case reports have suggested an association between IV vitamin C and urinary oxalate excretion. Recently, the US Food and Drug Administration required the dose of vitamin C in IV multivitamin preparations to be increased from 100 mg to 200 mg/d. We compared the urinary oxalate excretion level in stable home total parenteral nutrition (TPN) patients receiving both doses of vitamin C. Methods: Each participant provided a 24-hour urine sample for oxalate determination on the vitamin C dose (100 mg/d), and again after at least 1 month on the increased vitamin C dose (200 mg/d). A 2-day diet diary was completed covering the day before and the day of the urine collection and was analyzed for oxalate and vitamin C content. Comparisons were made using Student paired t test and Wilcoxon signed rank. Results: Thirteen patients (7 males/6 females) aged 63.1 ± 12.2 years who had no history of nephrolithiasis and had received TPN for 55.9 ± 78.8 months were enrolled. The most common indication for TPN was short bowel syndrome (38.5%). Eight patients had an intact colon. Urinary oxalate excretion increased on the 200-mg vitamin C dose, from 0.34 ± 0.13 to 0.44± 0.17 mmol/d (mean increase = 0.10 mmol/d; p = .04; 95% confidence interval 0.004 to 0.19 mmol/d). Oral intake of vitamin C and oxalate did not differ between the 2 collection periods. Conclusions: In therapeutically used doses, IV vitamin C increases urinary oxalate excretion, potentially predisposing susceptible individuals to nephrolithiasis. This factor should be considered in patients receiving home TPN.
Urinary oxalate increased from 0.34 ± 0.13 to 0.44 ± 0.17 mmol/d (p = .04) when the dose of IV vitamin C was increased from 100 to 200 mg/d in a group of patients (63.1 ± 12.2 years) without a history of nephrolithiasis receiving chronic home total parenteral nutrition (duration 55.9 ± 78.8 months).
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