Dementia-related psychosis readout could lead to label expansion for Acadia's Nuplazid

A new Phase III readout could speed Acadia's timeline to a potential regulatory submission of pimavanserin to treat dementia-related psychosis, an indication that afflicts a much larger population than the one for which the molecule is already approved as Nuplazid.

Acadia Therapeutics Inc. (NASDAQ:ACAD) climbed $15.05 (63%) to $38.85 on the news, adding more than $2.1 billion in market cap, on Monday after the company said it would stop early the Phase III HARMONY trial of pimavanserin to treat dementia-related psychosis based on interim data that met criteria requiring a one-sided p-value of less than 0.0033 on the study's primary endpoint, which measured time to relapse.

Top-line data were due in 2H20, but a prespecified stopping rule allowed for the trial to end earlier if statistical significance met a "very high" threshold at the interim analysis, President Srdjan Stankovic said during Acadia's 2Q19 earnings call in late July.

HARMONY's design included an open-label period, followed by a randomized, double-blind portion in which placebo or pimavanserin was given only to patients who met response criteria during the first stage. There are no approved treatments for dementia-related psychosis.

Acadia now hopes to meet with FDA and then submit an sNDA next year for pimavanserin. On a conference call Monday, Stankovic said the company and FDA had agreed at an end-of-Phase II meeting that Acadia could submit pimavanserin for the dementia indication based on "a single well-controlled study whose results were both statistically and clinically very persuasive."

According to Acadia, about 1.2 million patients in the U.S. have been diagnosed with dementia-related psychosis -- about half of the 2.4 million who have the disorder, which represents about 30% of the roughly 8 million U.S. patients with dementia.

Approval in the dementia indication would open up a substantially larger market for Acadia beyond Nuplazid's approved indication: hallucinations and delusions related to Parkinson's disease psychosis. "The addressable population for dementia-related psychosis is approximately tenfold larger than Parkinson's disease psychosis," CEO Stephen Davis said on Monday's call.

Acadia is conducting two Phase III trials of pimavanserin as an adjunctive treatment for major depressive disorder. The company said the potential U.S. market in that indication includes roughly 2.5 million patients.

Nuplazid's label carries a black box warning noting a risk of increased mortality in elderly patients with dementia-related psychosis. On the call, Stankovic said no new safety concerns emerged in HARMONY.

Sales of Nuplazid grew 38% to $146.2 million in 1H19 from $105.9 million in 1H18. The drug is a small molecule serotonin receptor 2A (5-HT2A; HT2RA) receptor inverse agonist.

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