Satralizumab is a recombinant humanized monoclonal antibody targeted against human interleukin-6 (IL-6) receptors, similar to tocilizumab, which is produced in Chinese hamster ovary cells and based on an IgG2 framework. Satralizumab is used in the treatment of neuromyelitis optica spectrum disorder (NMOSD), a rare autoimmune inflammatory disorder of the central nervous system (CNS) involving demyelinating lesions in the optic nerve, spinal cord, brainstem, and cerebrum. Some of the pro-inflammatory mechanisms involved in NMOSD are thought to be mediated, at least in part, by IL-6, including increased production of anti-aquaporin-4 (AQP4) autoantibodies and increased permeability of the blood-brain barrier, which allows for the passage of pro-inflammatory mediators into the CNS. Satralizumab is thought to exert its therapeutic benefits by blocking IL-6 receptors and, subsequently, these inflammatory responses. Enspryng®, a satralizumab formulation developed by Chugai Pharmaceutical and Roche, is uniquely formulated with "recycling antibody technology" whereby the association of satralizumab to IL-6 receptors occurs in a pH-dependent manner - this allows satralizumab to bind an IL-6 receptor until it reaches an endosome, after which the drug may dissociate from the receptor and move back into the plasma to act again. This novel mechanism effectively increases the duration of action of satralizumab, as it allows for single drug molecules to interact with multiple endogenous IL-6 receptors prior to elimination. Satralizumab was first approved for use in Canada in June 2020 for the treatment of AQP4 antibody-positive patients with NMOSD. It received subsequent approvals in Switzerland and Japan, and was approved for use by the FDA in August 2020, becoming the 3rd treatment to receive FDA approval for NMOSD (after eculizumab in June 2019 and inebilizumab in June 2020).