Idursulfase

Elaprase (Genzyme)
5 mL glass vials containing 2 mg/mL concentrate solution for infusion
Approved indication: Hunter syndrome
Australian Medicines Handbook Appendix A

Hunter syndrome is a very rare lysosomal storage disease. Patients have a deficiency of the enzyme iduronate sulfatase and this leads to an accumulation of mucopolysaccharides. (Hunter syndrome is also known as mucopolysaccharidosis II.) Early onset of this X-linked disorder results in developmental delay, coarse facial features, impaired vision, deafness, stiff joints, hepatosplenomegaly and cardiorespiratory problems.

Idursulfase is a genetically engineered form of iduronate sulfatase. A solution of the enzyme is diluted and infused over 1-3 hours. Although it only has a half-life of approximately 45 minutes, idursulfase only needs to be infused once a week.

The efficacy of enzyme replacement therapy was assessed in 96 patients with a median age of approximately 14 years (range 5-31 years). These patients were randomised to receive a weekly infusion of idursulfase or placebo or an infusion of idursulfase every other week. After a year, liver volume had decreased by approximately 25% with enzyme replacement. Lung function (absolute forced vital capacity) improved, but was only significantly better than placebo with weekly infusions. From a baseline mean of 396 metres, the distance the patients could walk in six minutes increased by 44 metres with weekly infusion, 30 metres with infusions every other week and 7 metres with placebo.¹

Adverse reactions which occurred more frequently with idursulfase than with placebo included headache, abdominal pain, arthralgia and rashes. Many reactions were infusion-related so the infusion may need to be slowed or stopped. Life-threatening anaphylaxis has been reported and these reactions may have a delayed onset. Patients who develop antibodies to idursulfase have an increased incidence of infusion reactions.

While the evidence shows that weekly infusions improve walking capacity, more research is needed to show if idursulfase has any effect on the progression of Hunter syndrome. The main trial of idursulfase did not report on the neurological aspects of the syndrome.¹ It is also unclear if the development of antibodies will eventually lead to a loss of efficacy. Although idursulfase replaces the deficient enzyme, it cannot be regarded as a cure for Hunter syndrome.

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The Transparency Score is explained in New drugs: transparency', Vol 37 No 1, Aust Prescr 2014;37:27.

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