Some investigators have used the parenteral formulation orally to treat patients with hairy cell leukemia. About 37–51% of oral cladribine is bioavailable orally. It is used, often in combination with other cytotoxic agents, to treat various kinds of histiocytosis, including Erdheim–Chester disease and Langerhans cell histiocytosis.Following EMA approval of cladribine tablets for the treatment of adult patients with highly active relapsing-remitting multiple sclerosis in 2017, as of July 2020, cladribine tablets have gained marketing authorisation in over 75 countries. In 2019, cladribine tablets were approved by the FDA for the treatment of relapsing forms of multiple sclerosis, to include relapsing-remitting disease and active secondary progressive disease, in adult patients who have had an inadequate response to, or are unable to tolerate, an alternate drug indicated for the treatment of multiple sclerosis.Cladribine may cause foetal harm when administered to a pregnant woman and is listed by the FDA as pregnancy category D; safety and efficacy in children has not been established. Mechanism of action
As a purine analogue, cladribine (2-chloro-2-deoxyadenosine [2-CdA]) is taken up into rapidly proliferating cells, including B and T lymphocytes, to be incorporated into DNA synthesis. Chemically, it mimics nucleoside adenosine; however, unlike adenosine, cladribine has a chlorine molecule at position 2, which renders it partially resistant to breakdown by adenosine deaminase. This causes it to accumulate in cells and interfere with the targeted cells ability to process DNA.Cladribine is taken up by specific nucleoside transporter proteins.
This reduction correlated with a reduced risk in disability progression in a retrospective analysis.In clinical trials, higher cumulative doses of cladribine tablets did not result in further improvement in efficacy nor did additional courses after the 2-year treatment period, but was associated with a higher incidence of Grade 3 and Grade 4 lymphopenia. Safety profile of cladribine tablets in multiple sclerosis
Cladribine tablets target the cells of the adaptive immune system with minimal impact on innate immune cells. Although the exact mechanism by which cladribine exerts its therapeutic effect is not fully elucidated, it is proposed to have a transient effect on B and T lymphocyte depletion, interrupting the cascade of immune events central to multiple sclerosis. As a result, a reduction in lymphocyte count (lymphopenia) may be reported following treatment. In clinical trials, lymphocyte levels above Grade 0 (≥1000 cells/mm3) and Grade 1 (<1000–800 cells/mm3) were maintained in most patients, with levels continuing to improve after the 2-year dosing period. Less than 1% of patients developed Grade 4 lymphopenia (<200 cells/mm3). It is important that patients with lymphocyte counts below 500 cells/mm3 should be actively monitored for signs suggestive of infection and that anti-infective treatments are given to at-risk patients.Despite the initial reduction in lymphocyte counts following treatment, studies showed the overall risk of infection in patients receiving cladribine tablets was comparable to those who received placebo, except for herpes zoster infection.