The US Food and Drug Administration (FDA) has declined to approve Irish biopharmaceutical company Alkermes’ depression drug ALKS 5461, and requested additional clinical data.

Alkermes submitted a new drug application (NDA) to the FDA in February last year, seeking approval for ALKS 5461 as an adjunctive treatment for major depressive disorder (MDD).

The therapeutic is an investigational, oral, once-daily fixed-dose combination of buprenorphine and samidorphan.

Buprenorphine is a partial mu-opioid receptor agonist and kappa-opioid receptor antagonist, while samidorphan is a mu-opioid receptor antagonist.

ALKS 5461 is designed to act as an opioid system modulator. It is intended for MDD patients who experience an inadequate response to conventional antidepressant therapies.

In a complete response letter (CRL) regarding ALKS 5461’s NDA, the US regulatory agency said that additional substantial evidence is required to support the drug’s effectiveness.

“Alkermes plans to meet with the FDA to discuss the contents of the CRL and potential next steps for ALKS 5461.”

Responding to the letter, the company said: “Alkermes plans to meet with the FDA to discuss the contents of the CRL and potential next steps for ALKS 5461. This interaction with the Agency will inform whether there is a viable path forward for the ALKS 5461 programme.”

The NDA included findings from a clinical efficacy and safety package comprising data from more than 30 clinical trials and more than 1,500 patients with MDD.

During the clinical development programme, ALKS 5461 demonstrated a consistent antidepressant activity, safety and tolerability profile.

In April last year, the FDA sent a Refusal to File letter to Alkermes, saying that the NDA offers insufficient evidence of overall effectiveness to carry out a substantive review of the drug.

It recommended additional clinical trials and a bioavailability study to generate additional bridging data between ALKS 5461 and the reference listed drug, buprenorphine.