Effect of an Excess Dose of Cladribine on the Subsequent Therapeutic Regimen and Pregnancy

Cladribine is an oral immune reconstitution therapy approved for the treatment of highly active relapsing–remitting multiple sclerosis. It selectively reduces CD4 + and CD8 + T lymphocytes, induces an immune reconstitution effect, and enables a short treatment course with durable disease control. Although generally well tolerated, it is associated with dose-dependent adverse effects, most notably severe (grade III–IV) lymphopenia, reported in up to 40% of patients, particularly during the second treatment year. Strict adherence to weight-based dosing is therefore essential. Miscalculations of cumulative doses may lead to prolonged immunosuppression and related complications. We report a rare clinical case of excessive cumulative cladribine dosing and its subsequent clinical, hematological, and reproductive outcomes. To our knowledge, this is the first reported case describing the consequences of exceeding the cladribine dosage in multiple sclerosis.