WASHINGTON, Sept 13 (Reuters) — The common asthma drug albuterol can help patients with multiple sclerosis, perhaps by tamping down an overactive immune system, US researchers reported.

The cheap pill, available generically, may enhance the effects of a standard MS treatment called glatiramer, the researchers reported in the Archives of Neurology.

The Multiple Sclerosis Association of America estimates that 350,000 to 400,000 Americans have MS, which has no cure. Treatments are often expensive so insurers and patients would welcome cheap, generic drugs that can help the disease, which most frequently affects young adults.

Dr. Samia Khoury of Brigham and Women's Hospital and Harvard Medical School in Boston and colleagues tested 39 patients with relapsing-remitting MS, a form of the disease that has an uncertain progression.

Patients got injections of glatiramer, an MS drug sold under the brand name Copaxone by Teva Pharmaceutical Industries Ltd. Half got a placebo pill and half got albuterol, sold in Europe under the name salbutamol.

The patients were followed and examined for a year, with tests of their blood, and scans of their brains. Few patients had relapses. But those who got both drugs had 0.09 relapses over the year on average, while those that got a placebo had a relapse rate of 0.37 per year, the researchers found.

Those taking albuterol went longer before their first relapse, the researchers found.

"We conclude that treatment with glatiramer acetate plus albuterol is well tolerated and improves clinical outcomes in patients with multiple sclerosis," Khoury's team wrote.

Multiple sclerosis is characterised by the loss of the fatty sheath that protects nerve cells, called myelin. It is believed to be caused by inflammation and patients often have elevated levels of interleukin-12.

Albuterol helps treat a constriction of the airways called bronchospasm that is one of the dangerous symptoms of asthma, and lowers interleukin-12. It is marketed by GlaxoSmithKline, Teva and other makers in both pill and inhalant form.

Teva is currently fighting in US federal court to protect its patent on Copaxone.