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(New throughout, adds comments from physicians and patients; adds byline)
By Toni Clarke
WASHINGTON, Jan 14 (Reuters) - A drug to treat a rare form of low blood pressure made by Chelsea Therapeutics International Ltd is effective enough to warrant regulatory approval, an advisory panel to the U.S. Food and Drug Administration concluded on Tuesday.
The panel voted 16 to 1 in favor of the drug, Northera, for patients with neurogenic orthostatic hypotension (NOH), a rare, chronic type of low blood pressure that occurs on standing and is associated with certain neurological disorders such as Parkinson's disease.
Chelsea shares more than doubled in after-hours trading. The FDA is not bound to follow the advice of its panels but typically does so.
Panelists wrestled with gaps in the clinical data which they said made it difficult to determine whether the drug, which appears effective after one week's treatment, is effective over the long term. Most suggested the company be required to conduct a follow-up study to prove a durable benefit.
Dr. James de Lemos, a cardiologist and professor of medicine at the University of Texas Southwestern Medical Center, said he voted in favor "based on the compelling evidence of suffering and the absence of viable alternatives," but said the approval should be conditional on further study.
Patients and patient advocates testified before the panel about the positive impact the drug has had on their lives.
Gail Hershkowitz, 65, a retired music teacher who lives in Boynton Beach, Florida, was diagnosed with Parkinson's disease 15 years ago and, later, with NOH. She said in an interview that she became afraid to leave her house after fainting and vomiting multiple times in public. She took Northera as part of a clinical trial and says it has enabled her to lead a relatively normal life.
But some panelists expressed frustration that the experience of patients who have benefited from the drug was not clearly backed up by data from the clinical trials.
A reviewer for the FDA, Dr. Shari Targum, said in preparatory documents published on Friday that she did not think the data was strong enough to support approval.
Chelsea's shares fell as much as 36 percent following that review. They were halted during the panel meeting on Tuesday, and rose to $5.78 in after-hours trading from a close on Monday of $2.30
Northera, also known as droxidopa, is converted by the body into norepinephrine, a chemical messenger that sends signals to blood vessels and the heart to regulate blood pressure. Insufficient norepinephrine can lead to light-headedness and fainting upon standing.
Chelsea originally filed for approval of droxidopa in 2011, based on a study known as 301. In February, 2012, an FDA advisory panel recommended approval of the drug, but the agency rejected it and asked for additional data.
The company sought to address the FDA's concerns using data from a different study known as 306B, but the FDA denied the request and said an additional trial would be needed.
Chelsea appealed the decision, and in early 2013 the FDA agreed to accept a resubmission based on data from the 306B study, saying that while short-term data, if convincing, would be adequate for approval, a post-approval study could be required to prove the results were durable.
Targum said the results of study 306B did not meet those criteria. Most panelists, however, said that while there was no convincing evidence that the drug provides a durable benefit, there was no convincing evidence to show that it does not show a benefit.
"This is a terrible disease and there are no other effective medications," said Dr. Vasilios Papademetriou, a cardiologist and professor of medicine at Georgetown University. Although the studies were not perfect, he said, "the data convinced me there is a long lasting benefit in some patients."
Chelsea licensed rights to the drug outside Asia from Dainippon Sumitomo Pharma in 2006. It was introduced in Japan in 1989. (Reporting by Toni Clarke in Washington. Editing by Andre Grenon and David Gregorio)