Hunter syndrome medical therapy
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:
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Overview
On July 24, 2006, a synthetic version of I2S, called Elaprase (Idursulfase), was approved by the United States Food and Drug Administration as an enzyme replacement treatment for Hunter syndrome. Elaprase is a purified form of the lysosomal enzyme iduronate-2-sulfatase and is produced by recombinant DNA technology in a human cell line. Elaprase may be one of the most expensive drugs ever produced, with an estimated cost of USD300,000 per patient, per year. [1]
Medical Therapy
Idursulfase
A 53-week, randomized, double-blind, placebo-controlled Phase II/III trial demonstrated that Elaprase provides clinically important benefits to Hunter syndrome patients. The primary efficacy endpoint of the trial was a composite analysis of changes from baseline in two clinical measures: a 6-minute walk test and percent predicted forced vital capacity. Shire is pleased to report that this endpoint achieved statistical significance compared to placebo. After one year of treatment, patients receiving weekly infusions of Elaprase experienced a mean increase in the distance walked in six minutes of 35 meters compared to patients receiving placebo. Treatment with ELAPRASE was generally well-tolerated by patients in the Phase II/III trial. Adverse reactions were commonly reported in association with infusions, and were generally mild to moderate. The Elaprase label includes a boxed warning with information on the potential for hypersensitivity reactions. The boxed warning states that “Anaphylactoid reactions, which may be life threatening, have been observed in some patients during Elaprase infusions. Therefore, appropriate medical support should be readily available when Elaprase is administered. Patients with compromised respiratory function or acute respiratory disease may be at risk of serious acute exacerbation of their respiratory compromise due to infusion reactions, and require additional monitoring.”
In all phases of clinical study for Elaprase, eleven patients experienced significant hypersensitivity reactions during 19 of 8,274 infusions (0.2%) and no patients discontinued treatment permanently as a result of a hypersensitivity reaction. The most common adverse events observed in >30% of patients during the Phase II/III trial were pyrexia, headache and arthralgia.
Fifty-one percent (32 of 63) of patients in the weekly Elaprase treatment arm in the pivotal clinical study (53-week placebo-controlled study with an open-label extension) developed anti-idursulfase IgG antibodies.
Elaprase was originally developed by a company called Transkaryotic Therapies (TKT) of Cambridge, MA. TKT was acquired by Shire in 2005. [2]