Safety and tolerability of cladribine tablets in multiple sclerosis: The CLARITY (CLAdRIbine Tablets treating multiple sclerosis orallY) study

Background: Cladribine is a synthetic deoxyadenosine analogue in development as an oral multiple sclerosis (MS) therapy. Objective: To report in detail the safety findings from the 96-week, phase III, double-blind CLARITY study, which evaluated treatment with cladribine tablets in relapsing-remitting MS. Methods: A total of 1,326 patients were randomized 1 : 1 : 1 to two short-course regimens of cladribine tablets (3.5 or 5.25 mg/kg cumulative dose over 96 weeks) or placebo. Safety assessments included monitoring for adverse events (AEs), routine physical and neurologic examinations and frequent laboratory parameter assessments. Results: Of the randomized patients, 88.6% completed treatment with cladribine tablets versus 86.3% with placebo. Lymphopenia was the most commonly reported AE in patients treated with cladribine tablets and was anticipated based on the mechanism of action. The incidence of infections was 48.3% with cladribine tablets and 42.5% with placebo, with 99.1% and 99.0% rated mild-to-moderate by investigators. Herpes zoster infections developed in 20 (2.3%) cladribinetreated patients; all cases were dermatomal. There were no herpes zoster infections in the placebo group. Nine (1.0%) patients experienced events related to uterine leiomyomas in the cladribine tablets groups versus one (0.2%) with placebo. Three isolated cases of malignancy were reported in cladribine-treated patients during the study; a fourth was reported during post-study surveillance. A pre-malignant cervical carcinoma in situ was also reported. The incidence of malignancies during the study did not exceed the expected rate in a population standardized for country, gender and age. Conclusion: The safety and tolerability profile observed in the CLARITY study together with the reported efficacy support the potential for cladribine tablets as an MS therapy.