Urinary oxalate excretion increases in home parenteral nutrition patients on a higher intravenous ascorbic acid dose.
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.
Peña de la Vega
Lourdes
L
Mayo Clinic Hyperoxaluria Center and the Mayo Clinic College of Medicine and Division of Nephrology, Department of Internal Medicine, Rochester, Minnesota 55905, USA.
Lieske
John C
JC
Milliner
Dawn
D
Gonyea
Janelle
J
Kelly
Darlene G
DG
D000328:Adult; D000368:Aged; D000975:Antioxidants / Q000008:administration & dosage / Q000378:metabolism; D001205:Ascorbic Acid / Q000008:administration & dosage* / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007408:Intestinal Absorption; D008297:Male; D008875:Middle Aged; D010070:Oxalates / Q000652:urine*; D016331:Parenteral Nutrition, Home / Q000009:adverse effects*
D000975:Antioxidants; D010070:Oxalates; D001205:Ascorbic Acid