Effect of repeated treatments with cladribine (2-chlorodeoxyadenosine) on blood counts in multiple sclerosis patients

We report the results of blood morphology monitoring of 11 remitting-relapsing multiple sclerosis patients who received repeated treatments with cladribine (2-chlorodeoxyadenosine). The drug was given once, daily, subcutaneously (5 mg) or orally (10 mg) for 5 consecutive days, as 6 monthly courses followed by one or two additional courses at 3 or 6 month intervals. The treatments were well tolerated, although many patients suffered from incidental upper respiratory tract infections, most of which occurred during the last 6 months of the observation period. One patient had recurrent infections, including an episode of urosepsis. All infections responded to standard therapy with antibiotics. Progressive lymphocyte reduction to 1000/microliters on average, and clear, but clinically insignificant drop in thrombocytes, was observed. Granulocyte counts were sometimes markedly elevated. A few patients developed macrocytosis, but none required transfusion. With our dosing and schedule, cladribine seems relatively safe in multiple sclerosis patients.