The safety profile of low-dose cladribine in refractory rheumatoid arthritis. A pilot trial

Cladribine (2-chlorodeoxyadenosine, 2-CdA) is a newer purine analog with specific toxicity to lymphocytes. As lymphocytes play a major role in rheumatoid arthritis (RA), we assessed the safety profile of low-dose 2-CdA in patients who were refractory to more than three disease-modifying drugs. Five patients were given a subcutaneous dosage of 0.05 mg/kg 2-CdA weekly over a period of 8 weeks. Of the lymphocyte subsets, both T and B cells decreased below the normal range, whereas natural killer cells remained stable. These changes were the only side-effects noted during treatment and 4 weeks afterwards. In one patient a pacemaker was implanted for reasons unlikely to be related to 2-CdA administration. We conclude that even low-dose 2-CdA (0.05 mg/kg) can decrease T and B cell populations in patients with refractory RA, but other side-effects are unlikely. For assessing the possible clinical efficacy of low-dose 2-CdA further studies are warranted.