Elaprase (idursulfase)

The standard of care for the somatic disease in Hunter syndrome since 2006 and the only option for patients outside the Avlayah label: adults, patients with the attenuated non-neuronopathic form, and children whose neurologic disease has already advanced.

Hunter syndrome is an X-linked disease in which the body lacks iduronate-2-sulfatase, one of the enzymes that dismantles long sugar chains called glycosaminoglycans inside cells. Without it, heparan sulfate and dermatan sulfate pile up in the lysosomes of cells across the body, enlarging organs, stiffening joints, narrowing airways and, in the severe form, damaging the brain. Elaprase is a manufactured copy of the enzyme, infused weekly, that cells take up and use to clear the backlog. Its limit is the blood-brain barrier: the enzyme is too large to cross it, so Elaprase treats the body's disease and not the neurologic disease that defines severe Hunter syndrome.

Elaprase carries a boxed warning for anaphylaxis, which the label notes has occurred during infusions and up to 24 hours afterward, regardless of how long a patient has been on treatment, and which has included respiratory distress, low oxygen, low blood pressure, hives and swelling of the throat or tongue. Infusions are given by staff trained in resuscitation with emergency services accessible. The label singles out a higher-risk group: children aged 7 and younger whose Hunter syndrome is caused by a complete gene deletion, large rearrangement, nonsense, frameshift or splice-site mutation had more hypersensitivity reactions, serious reactions and anti-drug antibodies. Patients with compromised breathing or an acute respiratory illness may be at higher risk from a reaction, and delaying the infusion is an option. Patients who are prone to fluid overload, or whose heart or lung function is weak, can have a serious worsening of their heart or breathing during infusions and may need extra monitoring and longer observation. The most common reactions in patients 5 and older were headache, itching, musculoskeletal pain, hives, diarrhea and cough; in children 7 and younger, fever, rash, vomiting and hives.

A weekly, lifelong enzyme replacement biologic for an ultra-rare disease, among the most expensive chronic therapies in medicine on an annual basis. Coverage is well established after 20 years on the market, which makes the practical question continuity rather than approval.

Pick your insurance to see which help fits. Drugmaker copay cards can't be used with Medicare, Medicaid or TRICARE; charity funds are the usual route there.

More ways to get help paying for treatment →

Approved for patients with Hunter syndrome. The label states it improves walking capacity in patients 5 and older, that in children 16 months to 5 years it reduces spleen volume without demonstrated symptom benefit, and that safety and efficacy under 16 months are not established. Since March 2026, children with neuronopathic disease and preserved neurologic function may be candidates for Avlayah instead; the Avlayah label advises against combining the two.

Source: FDA Drugs@FDA (BLA 125151)

Access program details are provided for informational purposes and may vary based on insurance coverage, geographic location, and individual circumstances. Confirm current eligibility directly with the manufacturer or your specialty pharmacy.

The pivotal trial was a 53-week randomized, double-blind, placebo-controlled study of 96 patients aged 5 to 31 with reduced lung function, comparing weekly Elaprase, every-other-week Elaprase and placebo. The primary endpoint combined change in 6-minute walk distance with change in percent-predicted forced vital capacity. Weekly Elaprase beat placebo on the composite (p=0.0049), driven by walking: patients on weekly treatment walked 35 meters farther after a year than those on placebo (p=0.01). The change in lung function was not statistically significant. In children aged 16 months to 5 years, the label notes that spleen volume fell as it did in older patients but that no data show improvement in symptoms or long-term outcomes.

Developed by Shire Human Genetic Therapies and approved by the FDA on July 24, 2006 as the first treatment for Hunter syndrome. Shire was acquired by Takeda in 2019, which now markets it. For 2 decades it was the only option, and its inability to cross the blood-brain barrier defined the disease's central unmet need until Avlayah, a brain-penetrant version of the same enzyme, was approved in March 2026.