European regulators have accepted for review Merck's application to market investigational drug cladribine for the treatment of relapsing-remitting multiple sclerosis.

The submission is based on data from three Phase III studies, CLARITY, CLARITY EXTENSION and ORACLE MS, and the Phase II ONWARD study, in which the drug showed significantly reduced relapse rates, risk of disability progression and development of new MS lesions, as detected by MRI, versus placebo in patients with the disease.

Alongside interim long-term data from the prospective registry, PREMIERE, the application also includes follow-up consisting of over 10,000 patient years of exposure in total, Merck noted.

MS is a chronic, inflammatory condition of the central nervous system thought to affect around 2.3 million people worldwide. The most common symptoms include blurred vision, numbness or tingling in the limbs and problems with strength and coordination.

"Although there are multiple therapies available for relapsing-remitting MS, there is still a significant unmet medical need with a focus on efficacy, dosing, durability and safety," said Luciano Rossetti, head of global R&D for the German drugmakmer's Biopharma business.

"We believe that Cladribine Tablets, if approved, would have a first-of-its-kind dosing regimen and serve as an important therapeutic option for patients with relapsing-remitting MS."

Cladribine is an oral small molecule prodrug that selectively and periodically targets lymphocytes thought to be integral to the pathological process of MS.

However, the drug has met a number of setbacks on its path to market. Back in 2011, Merck said it wouldn't pursue further regulatory approvals for cladribine after receiving rejections from both the US Food and Drug Administration and European Medicines Agency, with requests for more data.