Results published in the New England Journal of Medicine showed that 33% of patients taking the drug deteriorated over time compared with 39% of those taking a placebo.
The study of patients with progressive MS found that patients taking the drug also displayed less brain loss in scans and scored better on the time needed to walk 7.6m.
MS is an incurable neurological disease in which the immune system mistakes myelin, a protective nerve coating, for a foreign body and attacks it.
The damage disrupts messages travelling along nerve fibres. It is like a damaged electrical cable where the flex is broken, and the wires are exposed.
Around 8,000 people in Ireland have MS and around 250 are diagnosed with the neurological condition every year.
As well as myelin loss, there can also sometimes be damage to the actual nerve fibres. It is this nerve damage that causes disability to occur and worsen over time.
The research involved testing on more than 700 patients by scientists in institutions in the US and Europe. It was sponsored by Ocrelizumab’s manufacturer, Roche.
The drug has been accepted for review for use by the European Medicines Agency and the US Food and Drug Administration.
Researchers have also suggested that the drug can prevent deterioration in patients with relapsing- remitting MS.
Two other trials also showed the drug’s ability to treat relapsing MS, characterised by distinct attacks which come and go.
In one study of 1,656 patients with relapsing- remitting MS, the relapse rate with Ocrelizumab was half what it was with a different drug.
The most common type of MS is relapsing-remitting. During remissions, a person would have fewer or no symptoms. Relapses tend to be unpredictable, and their causes are unclear.
Neurologist, Prof Gavin Giovannoni from Barts and the London School of Medicine and Dentistry, who was involved in the trials, said the results were “very significant”.
“The results shown by these studies have the potential to change how we approach treating both relapsing and primary progressive MS,” said Prof Giovannoni.
American neurologist Peter Calabresi wrote in the journal: “This is the first drug to show a significant effect in slowing disability progression in a phase three trial in primary progressive multiple sclerosis, and therefore the trial represents a landmark study in the field.”
MS Ireland said Ocrelizumab would be a welcome addition to the drugs currently licensed for relapsing-remitting MS and may also be beneficial to people with primary progressive MS.
However, MS Ireland, which supports people with MS, believes it could be late next year before the drug is licensed in Ireland and it then has to go through the process for the reimbursement of new medications.
MS Ireland chief executive, Ava Battles, said: “MS Ireland believes that people with MS should have access to all and any appropriate and licensed treatments that would improve or assist in the management of their condition.”