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The Food and Drug Administration said Friday it had approved the first new drug in 20 years to treat the paralyzing disease ALS.

The drug is not a cure but can slow down the inexorable worsening of the disease, which gradually paralyzes patients completely. It's always fatal and there is no cure.

Amyotrophic lateral sclerosis (ALS), sometimes known as Lou Gehrig's disease, is rare and affects between 12,000 and 15,000 Americans, according to the Centers for Disease Control and Prevention.

The new drug, called Radicava or edaravone, was developed in Japan, where it was approved to treat strokes.

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"After learning about the use of edaravone to treat ALS in Japan, we rapidly engaged with the drug developer about filing a marketing application in the United States," said Dr. Eric Bastings, deputy director of the Division of Neurology Products at FDA.

"This is the first new treatment approved by the FDA for ALS in many years, and we are pleased that people with ALS will now have an additional option," he said.

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It's in fact the first new drug approved for ALs since 1995, when riluzole, sold under the brand name Rilutek, was approved.

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Radicava is given in the form of an intravenous infusion, with two weeks of daily treatments followed by a two week break.

Tests on a very small group of 137 patients showed those who got the drug had slower declines compared to those who did not.

It comes at a price. Mitsubishi Tanabe Pharma America says the drug will cost more than $1,000 per infusion.

"If taken annually for 12 months or 13 cycles, according to the dosing and administration in the label, the cost before government discounts, will be $145,524," the company said.

"We will offer co-pay assistance for commercially insured patients to help reduce their out-of-pocket costs," the company added. "The price of Radicava is at the mid-point for an orphan drug in the U.S. and represents the investments MT Pharma America is making to deliver it to U.S. patients."

An orphan drug is one that is unlikely to have many buyers, so the FDA speeds approval.

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Radicava is what's known as a free radical scavenger. It appears to react with nerve-damaging compounds generated as part of the disease process.

It can have severe side effects.

"Radicava is also associated with serious risks that require immediate medical care, such as hives, swelling, or shortness of breath, and allergic reactions to sodium bisulfite, an ingredient in the drug. Sodium bisulfite may cause anaphylactic symptoms that can be life-threatening in people with sulfite sensitivity," the FDA said.

Rilutek has a different method of action, helping to stop nerve cell death, but only for a short time and it only extends the lives of patients by a few months on average.

ALS advocacy groups have been waiting eagerly for FDA’s approval of Radicava.