People with multiple sclerosis can have difficulty walking
A drug which allows multiple sclerosis patients to walk more quickly has passed the next step in its testing, say its makers.
The MS Society in the UK said that frampridine could have a real impact on the quality of life of some patients.
Drug company Acorda tested the drug on 240 patients, and found more than two-fifths of people showed improvement.
It plans to seek a US safety licence early in 2009.
Patients with MS often endure mobility problems, with many eventually needing the assistance of a wheelchair to get around as the condition progresses.
In MS, the body's own immune system turns on a fatty protein, myelin, that covers and insulates the signals travelling down nerve cells, which can lead to limb weakness, blurred vision and balance problems.
This drug is aimed at those who, as a result, are still capable of walking, but find it a slow and difficult process.
It works by slowing the loss of an chemical element, potassium, from nerve cells affected by the condition.
Those who benefited from the drug needed, on average, 25% less time to cover a distance of 25 feet (7.5m).
In addition, leg strength was found to improve among many of those taking the drug.
Ron Cohen, the chief executive of Acorda, said: "There is no approved treatment today that addresses walking disability for patients with multiple sclerosis.
"It is a fundamental feature of multiple sclerosis and one of the most worrisome features because it can imply loss of independence."
Although the drug improves mobility in some patients, there was no effect on the overall speed of progression of the disease, said the company.
A spokesman for the MS Society said that the plan to seek a US licence was "exciting news".
"MS can severely affect people's mobility, and in turn their sense of independence.
"The society would welcome any drug that is proven to help with walking disability and allow people with MS to regain some of their freedom."