Safety of OnabotulinumtoxinA with Concomitant Antithrombotic Therapy in Patients with Muscle Spasticity: A Retrospective Pooled Analysis of Randomized Double-Blind Studies

Background OnabotulinumtoxinA is approved as a treatment across multiple indications. For the treatment of spasticity, onabotulinumtoxinA is injected directly into affected muscles. Intramuscular injections may result in local bleeding and related complications, especially in patients receiving anticoagulant therapy. Despite anticoagulants being commonly used, there is limited information in the medical literature regarding the safety of intramuscular medications in patients receiving oral anticoagulants. This retrospective analysis included pooled safety data from Allergan-sponsored studies evaluating onabotulinumtoxinA for the treatment of patients with muscle spasticity. Objective The objective of this study was to determine the risk of bleeding complications in patients with post-stroke spasticity receiving antithrombotic therapy and intramuscular onabotulinumtoxinA. Methods We conducted a retrospective analysis of pooled safety data from 16 randomized, double-blind, placebo-controlled Allergan-sponsored studies of onabotulinumtoxinA for the treatment of post-stroke upper or lower limb muscle spasticity, including adult patients with at least moderate upper or lower limb spasticity and receiving at least one dose of the study drug. Bleeding-related adverse events starting within 4 weeks of study treatment were assessed. The incidence rates of bleeding complications were compared for patients receiving classes of antithrombotic therapy vs those not receiving antithrombotic therapy and for those receiving onabotulinumtoxinA vs placebo (with or without antithrombotic therapy). Results Of 1877 patients, 1182 received antithrombotic therapy. The overall incidence of bleeding complications was < 2%. In those receiving any antithrombotic therapy, the incidence of bleeding was 1.0% vs 1.4% (no antithrombotic therapy); after onabotulinumtoxinA, it was 0.9% for those receiving antithrombotic therapy vs 1.4% (no antithrombotic therapy), and for placebo 1.2% vs 1.4%, respectively. Subgroup results were similar. Conclusions No apparent increased risk of bleeding complications was observed following administration of onabotulinumtoxinA to patients receiving antithrombotic therapy. Nonetheless, patient education and careful observation of the injection site in patients receiving antithrombotic therapy remains warranted.