The Food and Drug Administration (FDA) has approved Mepsevii (vestronidase alfa-vjbk) for the treatment of Mucopolysaccharidosis VII (MPS VII, Sly syndrome) in pediatric and adult patients. This enzyme replacement therapy is intended to replace the deficient lysosomal enzyme beta-glucuronidase in MPS VII patients.

The approval of Mepsevii was based on a clinical trial program that included 23 patients with MPS VII; the patients ranged in age from 5 months to 25 years. Patients received Mepsevii at doses up to 4mg/kg once every two weeks for up to 164 weeks. Efficacy was primarily assessed through the 6-minute walk test (6MWT) in 10 patients who could perform the test. 

After 24 weeks, the mean difference in distance walked relative to placebo was 18 meters. Additional follow-up for up to 120 weeks suggested continued improvement in 3 patients and stabilization in the remaining 7 patients. After 120 weeks of exposure, 1 patient demonstrated a 21% improvement over baseline in forced vital capacity (FVC% predicted) on pulmonary function testing in addition to a 105 meter improvement in the 6MWT. Two other patients with baseline hepatosplenomegaly had reduction in liver volume (24% and 53%) and spleen volume (28% and 47%) after 36 weeks of Mepsevii treatment. The effect of Mepsevii on the central nervous system manifestations of MPS VII has not been determined. 

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The most common side of effects of treatment include infusion site reactions, diarrhea, rash, and anaphylaxis.

Mepsevii is supplied as a carton containing one 10mg/5mL single-dose vial. It is expected to be available later this month.

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