* Drug backed for condition tied to excess water
* Reviewer recommends against use in heart failure patients
* Cornerstone shares up 5.4 pct
WASHINGTON, Sept 11 (Reuters) - A clinical reviewer from the U.S. Food and Drug Administration on Tuesday recommended the agency approve Cornerstone Therapeutics Inc's drug to treat low sodium levels due to a condition that causes the body to have excess water.
However, the reviewer, Dr. Nancy Xu, said the drug lixivaptan should not be approved for heart failure patients, which Cornerstone had also sought.
Cornerstone shares were up 5.4 percent at $6.61 in morning trading on Nasdaq.
The FDA staff review comes ahead of an advisory panel of outside experts, which will vote on whether to recommend the drug on Thursday. The FDA will make a final decision later, taking into account the panel's recommendations.
Lixivaptan, from Cornerstone unit Cardiokine Inc, is meant to treat low sodium levels in the blood, known as hyponatremia. Although most people with the condition -- the most common electrolyte disorder in the United States -- have no symptoms, in severe cases it can cause swelling of the brain, respiratory arrest and death.
The condition affects up to six million Americans, according to the company, and is often tied to congestive heart failure.
Cornerstone had been seeking approval to use the drug in two conditions that can cause low sodium levels: congestive heart failure and syndrome of inappropriate antidiuretic hormone secretion (SIADH), which causes the body to develop excess water and is caused by improper chemical signals.
Xu recommended against the drug's use in heart failure patients because it was linked to more deaths during a clinical trial compared to placebo -- though it was uncertain whether the drug actually caused the deaths.
"There is currently insufficient information about the drug to determine whether the product is safe for use," she wrote in documents posted online on Tuesday.
She also said the drug's side effects in SIADH, such as low blood pressure, were not as great a concern.
Currently, low sodium levels tied to SIADH are treated with tolvaptan, made by Japanese drugmaker Otsuka Holdings Co , or by restricting how much water people drink, which is difficult to do precisely, the FDA reviewer said.