Allergan’s rapastinel has failed to hit its primary endpoints in three late-stage studies assessing its potential as an adjunctive treatment for depression.

In three acute studies (RAP-MD-01,-02,-03), the rapastinel treatment arms “did not differentiate from placebo on the primary and key secondary endpoints,” in patients with major depressive disorder, the firm said.

On the plus side, in all three studies rapastinel was well tolerated without any signal of psychotomimetic side effects.

In addition, an interim analysis of the rapastinel relapse prevention study (RAP-MD-04) suggests the primary and key secondary endpoints will not be met, Allergan stressed.

"We are deeply disappointed with these results, and they are a vivid reminder that drug development is extremely challenging, especially in mental health, said David Nicholson, chief R&D at the firm.

“We remain committed to the development of new life changing medications to combat the rising global toll of mental illness," he added. "We will evaluate the impact of these data on the ongoing monotherapy MDD program and suicidality in MDD study. We expect to make a decision on these programs during the course of 2019."

Rapastinel (formerly known as GLYX-13) is an investigational intravenous formulation of a novel NMDA receptor partial agonist which, the firm says, has shown a rapid onset of antidepressant efficacy one day after a single dose in a Phase II clinical trial of patients with MDD who had an inadequate response other antidepressants.

Around 16 million people in the US are living with MDD and despite available therapies, there remains an unmet need for agents that demonstrate a rapid onset of action,

Detailed results from the trials will are to be presented at future scientific meetings.