Alnylam rare disease drug may be delayed

Alnylam may have to put hold off plans for an early FDA approval for its gene-silencing drug givosiran – because recruitment to a rare disease trial is going better than expected.

Rare disease trials are notoriously difficult to conduct because of a paucity of available patients, but Alnylam said that the trial of givosiran in acute hepatic porphyria has attracted more participants than expected.

The firm had hoped to seek an accelerated approval from the FDA on early data before the trial completes – but because of the fast pace of enrolment, Alnylam said the regulator may choose to wait for full results.

Citing a company conference call, Reuters reported that this would push a filing back by four to six months.

“It is possible the FDA could ask [the] company to wait another 6 months until the full data is released,” an unnamed executive said.

Another concern could be safety - there were no deaths on the trial, but 22% of those on the drug reported serious side effects, compared with 10% of patients given a placebo.

There are no approved treatments for acute hepatic porphyria and the Cambridge, Massachusetts-based biotech reckons about 1,000 patients have a severe form of the disease, without around 5,000 suffering less frequent attacks.

Interim data revealed this week showed patients with the condition that were given givosiran had a significant reduction in aminolevulinic acid (ALA) protein in their urine.

High levels of ALA are considered to trigger an increase in the “attacks” experienced by patients.

There were no other details about efficacy, or further data on the drug’s safety, according to Reuters.

In August, Alnylam’s Onpattro (patisiran) became the first ever RNA interference drug approved by the FDA to treat the nerve damage caused by the rare disease hereditary transthyretin-mediated amyloidosis (hATTR) in adults.

The drug’s $450,000 per year price tag is expected to be mitigated by discounts and “value-based” deals with insurers.

Alnylam beat competition from biotech Ionis to get the approval, which is developing a rival hATTR drug, Tegsedi (inotersen).