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Hyperoxaluria: Hydration, Pyridoxine Are Key Tools.

WASHINGTON -- Hydration and pyridoxine supplementation are essential in treating people with hyperoxaluria, Dr. Stevan B. Streem said at an update on urolithiasis sponsored by the American Urological Association.

Restricting oxalate in the diet can help somewhat, but it doesn't have a huge impact on urinary oxalate levels, said Dr. Streem, head of the section of stone disease and endourology in the department of urology at the Cleveland Clinic Foundation.

Oxalate-rich foods include spinach, nuts, and chocolate. Tea is also high in oxalate.

An excessive amount of oxalate in the urine is among the conditions that increase the risk of calcium-containing kidney stones. This factor is the cause of about 8% of all calcium-containing stones.

Oxalate is the metabolic end product of glyoxalate, which is normally transaminated or detoxified to glycine and oxidized to oxalate. Oxalate forms an insoluble complex with calcium in the gut and urine, preventing absorption.

Endogenous causes of hyperoxaluria include a deficiency of pyridoxine, which is a cofactor in glyoxalate transamination, and ethylene glycol ingestion. Hyperoxaluria also can result from vitamin C supplements. Daily doses in the 500-mg range are not significant, but doses of 2 g or more a day can significantly increase urinary oxalate levels and cause problems for those prone to stone formation, Dr. Streem noted.

The least common endogenous cause of hyperoxaluria is congenital hyperoxaluria. This severe disorder is caused by the deficiency of a hepatic enzyme that reduces transamination of glyoxalate to glycine and causes an increase in oxidation to oxalate. These patients ultimately need a combined kidney and liver transplant to resolve their liver disorder, he said.

Not all patients with hyperoxaluria have a pyridoxine deficiency, but 200 mg to 400 mg of pyridoxine a day is sometimes highly effective, irrespective of the type of hyperoxaluria.

In most patients with mild hyperoxaluria, the problem is excess dietary oxalate. For the most part, these people can do more to prevent recurrent stones by restricting oxalate in their diet than by restricting calcium, Dr. Streem said.

"Calcium restriction for most patients with calcium oxalate stones is actually detrimental and makes them more prone to stones, possibly because the calcium is then not available to combine with oxalate in the gut" and prevent its absorption, he emphasized.

Another reason to restrict dietary oxalate "at least moderately" is that oxalate "is 10 times more important than calcium in determining when the urine is supersaturated," Dr. Streem added. "So even small changes in urinary oxalate can have a bigger impact than a small reduction in urinary calcium."

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Publication:Family Practice News
Geographic Code:1USA
Date:Apr 15, 2000
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