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WEDNESDAY, July 30, 2003 (HealthDayNews) -- Kidney failure patients on dialysis typically need vitamin D supplements to overcome their body's inability to manufacture the nutrient, but a new study suggests not all supplements are created equal.
Those taking a relatively new form of the substance, paricalcitol, had a 16 percent lower risk of early death than those on the older version, calcitriol, which is currently the standard of care in this country, the study found.
The effect was even greater among blacks and more than two dozen other subgroups of patients, and in no case did calcitriol outperform paricalcitol, the researchers say.
Study author Dr. Ravi Thadhani, a staff nephrologist at Massachusetts General Hospital, says the results are "in line with other data that there is a significant difference with respect to survival and other parameters." These include better control over key minerals in the blood that go amok in kidney patients, he says.
"Physicians need to factor that in" when considering what form of vitamin D supplements to give kidney patients, Thadhani adds. A report on the findings appears in the July 31 issue of the New England Journal of Medicine.
An estimated 400,000 Americans with malfunctioning kidneys are currently undergoing dialysis to help them clear their blood of waste products. Although the treatment is lifesaving, up to 20 percent of dialysis patients die each year, mostly the result of the heart and vessel disease that often follows kidney failure.
One consequence of kidney failure is that the body stops breaking down vitamin D into the form cells can use. As a result, the skeleton is stripped of calcium, weakening bones, while blood levels of another mineral, phosphorus, soar.
In response, the body makes more of a substance called parathyroid hormone. But the result is to draw more calcium away from the bones and into the blood. "The concern is that you calcify your blood vessels and demineralize your skeleton," explain Dr. Matthew Weir, a kidney specialist at the University of Maryland School of Medicine in Baltimore.
Excessive calcium in blood vessels is linked to heart attacks and strokes -- problems that are 10 to 100 times more common than usual in people with severe kidney failure.
To limit the harmful effects of kidney failure, doctors give roughly 90 percent of dialysis patients injections of the active form of vitamin D. Calcitriol has for years been the most commonly used version, but some people don't respond to the treatment. It also can lead to too much calcium in the bloodstream, which in turn can cause heart and vessel damage.
In 1998 the U.S. Food and Drug Administration approved another form, known as paricalcitol, which has been shown to act differently than its older cousin. Previous studies have shown the newer version is better able to suppress excess calcium and phosphorus.
Thadhani's group followed 67,000 dialysis patients being treated nationally at private clinics run by Fresenius Medical Care, a Lexington, Mass. dialysis company. Starting in January 1999, patients received either calcitriol or paricalcitol. Over the study period, approximately 16,500 swapped formulations.
Paricalcitol was better than calcitriol at bringing calcium and phosphate under control. The risk of death over the next two years among people taking paricalcitol was 16 percent lower than that among those on the other drug. For black patients, the risk was 20 percent smaller. In 28 of 42 subgroups, including patients in different age groups, of either gender and with different causes of kidney failure, paricalcitol was either as effective or more effective than calcitriol at reducing the risk of death.
More information
Try the National Kidney Foundation or the Kidney Dialysis Foundation.
