Merck has announced that the European Medicines Agency (EMA) issued a positive opinion regarding the authorisation of cladribine for the treatment of relapsing remitting multiple sclerosis (RRMS) in patients with high disease activity.

Cladribine was originally developed as an anti-cancer drug and marketed as Leustat. Its immunosuppressive properties prompted Merck to investigate it for the treatment of RRMS. Cladribine reduces the numbers of certain types of T-cells involved in abnormal immune responses, which attack the myelin sheath of nerve cells in RRMS patients.

Cladribine’s approval process for multiple sclerosis (MS) has been difficult. Cladribine was rejected by both the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) in 2011 due to concerns about an increasing risk of cancer and the drug’s effects on the immune system from its Phase III CLARITY trial.

Following the regulatory bodies’ decisions, Merck announced that the company would withdraw cladribine from the approval process and terminate its development. However, in 2015, Merck decided to revisit cladribine, as the company felt that the regulatory climate around high-efficacy treatment options in MS had changed.

Data from the original Phase III CLARITY trial was reanalysed and a follow-up trial was conducted and concluded that there was no increased risk of cancer. Based on the updated conclusion, Merck filed a new approval application for cladribine with the EMA in Europe in 2015 and is in discussions with the FDA in the US.

In its Phase III trials, cladribine reduced annualised relapse rate by 67% and the risk of six-month confirmed expanded disability status scale progression by 82% compared to placebo after two years of treatment. The latest positive opinion from the EMA paves the way for cladribine’s final approval, as the European Commission (EC), which has the final say, typically adopts the EMA’s view.

Currently, treatment options in MS patients with high disease activity are dominated by various high-efficacy monoclonal antibodies. Cladribine, as the first high-efficacy oral agent, if it is approved, will provide more choice to physicians and patients with high disease activity.