according to an integrated analysis of several clinical trials published in Multiple Sclerosis and Related Disorders.
Dr. Stuart Cook
The drug causes transient lymphopenia, as is to be expected from its mechanism of action, but most patients who receive cladribine do not have grade 3 or 4 lymphopenia, the authors wrote. In general, cladribine is not associated with an increased risk of infections or malignancy.
Data indicate that cladribine’s mechanism of action contributes to its durable clinical effect, despite the brief treatment periods. Clinical trials have provided information about the treatment’s safety and tolerability. To examine the treatment’s long-term safety, Stuart Cook, MD, of New Jersey Medical School, Newark, and his colleagues pooled data for patients with multiple sclerosis (MS) treated with cladribine tablets (3.5 mg/kg) as monotherapy or placebo in three phase 3 clinical trials (CLARITY, CLARITY Extension, and ORACLE-MS) and followed up in the PREMIERE registry. The investigators called these patients the monotherapy oral cohort.
To investigate the potential associations between cladribine and rarer adverse events such as malignancies, Dr. Cook and his colleagues examined data from patients with MS who received cladribine, regardless of the formulation or route of administration, or placebo (the all-exposed cohort). This cohort included data from the ONWARD trial, in which patients received cladribine tablets or placebo in combination with interferon-beta, as well as data from five trials in which patients received parenteral cladribine or placebo.
The monotherapy oral cohort included 923 patients who received cladribine and 641 who received placebo. The median age at enrollment in this cohort was approximately 36 years. The majority of patients were women and disease characteristics were balanced between arms. The all-exposed cohort included 1,926 patients who received cladribine and 802 who received placebo. The demographic characteristics of this cohort were similar to those of the monotherapy oral cohort.
In the monotherapy oral cohort, the incidence rate of treatment-emergent adverse events, in adjusted adverse events per 100 patient-years, was 103.29 for the active group versus 94.26 for controls. Lymphopenia (7.94 vs. 1.06) and decreased lymphocyte count (0.78 vs. 0.10) occurred more frequently in the active group than in the placebo group.
Herpes zoster also occurred more frequently in the cladribine group (0.83 vs. 0.20). However, cladribine was not associated with systemic serious disseminated herpes zoster. Furthermore, the investigators found no overall increased risk of infections, including opportunistic infections, with cladribine tablets versus placebo, except for herpes zoster.
In addition, Dr. Cook and his colleagues found no increase in malignancy rates among patients who received cladribine, compared with those who received placebo. They also found no increase in the incidence of malignancies over time in the cladribine group.
The adverse event profile for cladribine tablets (3.5 mg/kg) as monotherapy has been well characterized, the investigators wrote. The results of this analysis are broadly similar to the short-term adverse event results reported in the individual trials.
EMD Serono and Merck Serono, two affiliates of Merck in Darmstadt, Germany, sponsored the study. Merck manufactures cladribine.
SOURCE: Cook S et al. Mult Scler Relat Disord. 2018 Nov 18. doi: 10.1016/j.msard.2018.11.021.