Company: Merck Serono, Inc.
- Given orally, as one or two courses per year, depending on the study regimen
- Cladribine was being studied in RRMSCladribine predominantly affects peripheral blood lymphocytes (immune-system cells produced to fight infection and disease), with relative preservation of other cell types and components. It causes a preferential and sustained depletion of certain T cells in the immune system, as well as a decrease in B cells. (T and B cells are two types of lymphocytes.) Cladribine also seems to directly influence the overall T-cell response, which is believed to play a major role in the MS process.The two-year Phase III CLARITY trial of two levels of cladribine versus placebo involved 1,326 patients with RRMS. Each course consisted of once-daily administration for four-to-five consecutive days, and study patients took cladribine for a total of eight-to-20 days of treatment during the year. It met its primary endpoint, showing 55-to-58-percent reductions in annualized relapse rates and 31-to-33-percent reductions in disability progression, as well as a substantial reduction in lesion burden.
The ONWARD Phase II study of 200 individuals who have experienced at least one relapse while taking Rebif combines oral cladribine with Rebif. This study will determine whether the combination is more effective than Rebif alone.
The Phase III ORACLE MS study was designed to assess whether cladribine can delay the time to a second clinical demyelinating attack in 600 individuals who have had a first clinical demyelinating event, also referred to as clinically isolated syndrome (CIS).
The FDA gave Fast Track approval status to cladribine in July 2006. In March 2011, after an increase in malignancies was observed in patients in the cladribine clinical trials, the FDA announced that it would not approve oral cladribine for MS without more safety information. In June 2011, Merck Serono announced that they will not currently pursue global approval for Cladribine Tablets for the treatment of RRMS, but would continue existing clinical trials. The company may consider a reapplication if safety concerns are lessened. The experience with cladribine, while a setback for MS therapy, provides an important lesson in medication development – and a reminder that risks are as important as benefits in developing medications, and in offering these medications to patients.