Merck KGaA is planning to file cladribine, an investigational oral treatment for multiple sclerosis in mid-2009 on the back of some impressive late-stage data, helping the German firm steal a march on other developers of an MS pill.

The company’s Merck Serono unit has presented two-year data from the 1,326-patient CLARITY Phase III study which demonstrated that cladribine met its primary endpoint of significantly reducing annualised relapse rates in patients with relapsing-remitting MS compared with placebo. Specifically, patients given the lower cladribine dose experienced a 58% relative reduction in annualised relapse rates compared with placebo, while those in the higher-dose group achieved a reduction of 55%.

Merck also noted that the trial also met its secondary endpoints, including reduction of lesion activity, proportion of subjects relapse-free, and disability progression. The results also showed that the frequency of adverse events among patients given cladribine was low and comparable to those taking placebo, except the rate of lymphopenia was higher in the cladribine group. However, the latter was expected based on the drug's “presumed mechanism of action”.

Elmar Schnee, chief executive of Merck Serono, said that the CLARITY data “mark an important milestone in the assessment of investigational oral treatments for MS and that cladribine tablets have the potential to make a real difference in the lives of patient”. He added that based on the CLARITY study, cladribine will be registered to regulators in Europe and the USA by the middle of the year.

Around 2.5 million people worldwide suffer from MS and approved drugs are administered by injections. An oral treatment is seen as a major breakthrough and analysts believe that cladribine could have peak sales of up to 1.5 billion euros per year. If approved, it will eventually take the place of Merck's blockbuster MS drug Rebif (interferon beta-1a).

Merck will be hoping that cladribine will hit the market before other investigational oral compounds get to the regulators. Leading the pack is Novartis' FTY720 (fingolimod) and Tevas's laquinimod.