The US Food and Drug Administration has issued a green light for Valeant to market Siliq as a treatment for adults with moderate-to-severe plaque psoriasis, but with a boxed warning on suicide and a restricted prescriber programme.

The approval allows use of the injected drug to treat those who are candidates for systemic therapy or phototherapy and have failed to respond, or have stopped responding to other systemic therapies.

Siliq (brodalumab) is a novel human monoclonal antibody that binds to the interleukin-17 receptor and inhibits inflammatory signalling by blocking the binding of several types of IL-17 to the receptor. By stopping IL-17 from activating the receptor, the drug prevents the body from receiving signals that may lead to inflammation.

Its safety and efficacy were established in three randomised, placebo-controlled clinical trials with a total of 4,373 adult participants with moderate-to-severe plaque psoriasis who were candidates for systemic therapy or phototherapy, which showed that significantly more patients treated with Siliq compared to placebo had skin that was clear or almost clear.

On the safety side, suicidal ideation and behaviour, including completed suicides, have occurred in patients given Valeant's drug during clinical trials, the regulator noted, but said a causal association between treatment with Siliq and increased risk of suicidal ideation and behaviour has not been established.

However, because of the observed risk of suicidal ideation and behaviour, the drug's labelling includes a Boxed Warning and it is only available through a restricted programme under a Risk Evaluation and Mitigation Strategy (REMS), which requires that prescribers must be certified with the programme and counsel patients about this risk.

Also, patients must sign a Patient-Prescriber Agreement Form and be made aware of the need to seek medical attention should they experience new or worsening suicidal thoughts or behaviour, feelings of depression, anxiety or other mood changes.

The approval triggers a $130 million milestone payment to AstraZeneca as per the terms of a license agreement signed by the firms in July last year. Brodalumab is also under review in Europe, where LEO Pharma currently holds rights.