General Information

Elaprase (idursulfase) is a purified form of the lysosomal enzyme human iduronate-2-sulfatase of recombinant DNA origin. It is designed to replace the natural enzyme, increasing catabolism of certain accumulated glycosaminoglycans (GAG), which abnormally accumulate in multiple tissue types in patients with mucopolysaccharidosis II (MPS-II, or Hunter syndrome).

Elaprase is specifically indicated for the treatment of Hunter syndrome (Mucopolysaccharidosis II, MPS II) in adults and children ages 5 and older. The drug has been shown to improve walking capacity in these subjects.

Elaprase is supplied as sterile, aqueous clear to slightly-opalescent colorless solution for intravenous infusion. Recommended initial dosing is 0.5 mg/kg administered via weekly infusion. The initial recommended infusion rate is 8 ml/hr for the first 15 minutes, which may be increased at 8/ml/hr increments at 15 minute intervals barring appearance of infusion reactions, to a maximum of 100 ml/hr. Total infusion duration is generally 1-3 hours, and should not exceed 8 hours. Infusions may be slowed, temporarily stopped, or discontinued for that dose if infusion reactions occur (see Side Effects, below).

Side Effects

Adverse events associated with the use of Elaprase may include, but are not limited to, the following:

• pyrexia
• headache
• arthralgia
• limb pain
• pruitis
• hypertension
• malaise
• visual disturbance

In addition, Elaprase was shown to cause anaphylactic reactions in some patients during infusions. It is contraindicated in patients with comprised respiratory function or acute respiratory disease.

Mechanism of Action

Hunter's Syndrome is an X-linked recessive disease caused by insufficient levels of the lysosomal enzyme iduronate-2-sulfatase. This enzyme cleaves the terminal 2-O-sulfate moieties from the glycosaminoglycans (GAG) dermatan sulfate and heparan sulfate. Due to the missing or defective iduronate-2-sulfatase enzyme in patients with Hunter's Syndrome, GAG progressively accumulate in the lysosomes of a variety of cells, leading to cellular engorgement, organomegaly, tissue destruction and organ system dysfunction. Treatment of Hunter's Syndrome patients with Elaprase provides exogenous enzyme for uptake into cellular lysosomes. Mannose-6-phosphate (M6P) residues on the oligosaccharide chains allow specific binding of the enzymes to the M6P receptors on the cell surface, leading to cellular internalization of the enzyme, targeting to intracellular lysosomes and subsequent catabolism of accumulated GAG.

Clinical Trial Results

FDA approval of Elaprase was based on the results of one clinical trial. This randomized, double-blind, placebo controlled trial enrolled 96 subjects with Hunter's Syndrom, aged 5-31 years. Subjects received Elaprase 0.5mg/kg every week, Elaprase 0.5mg/kg every other week or placebo. The treatment duration was 53 weeks. The primary efficacy endpoint was a score based on the change from baseline to week 53 in distance walked during a 6 minute walk test and the change in forced vital capacity percentages. The primary endpoints showed the greatest statistical significant difference between the weekly Elaprase treated group and the placebo group (p=0.0049). The subjects in the Elaprase weekly group showed a 35 meter mean increase in distance walked versus the placebo group. There was not a statistically significant difference in forced vital capacity percentages between the groups.