The US biotech has been positioning the non-stimulant drug as a safer, more tolerable alternative to already-marketed non-stimulants for ADHD such as Eli Lilly’s Strattera (atomoxetine) and Shire’s Intuniv (guanfacine), both of which have cheap generic variants available in the US.

It is testing the drug in four placebo-controlled phase III trials, including two in children aged six to 11 that have just generated results, as well as two in adolescents aged 12 to 17, one of which will read out later this month and the other in early 2019.

The two trials in younger patients show that SPN-812 – also known as viloxazine hydrochloride – both showed that the drug performed significantly better than placebo on hyperactivity, impulsivity and inattention scales, sufficient for Supernus to say it will press ahead with plans for a regulatory filing with the FDA in the second half of 2019.

Despite the company’s upbeat assessment – perfectly reasonable since the drug hit all its objectives in the two studies – shares nevertheless fell more than 13% after the data were announced. The problem is that questions are being asked as to whether SPN-812 is sufficiently better than a generic non-stimulant drug to justify a brand name price.

On a conference call to discuss the results, Supernus’ chief executive Jack Khattar pointed to a rapid onset of action, with statistical significance for improvement over control on two doses (100 mg and 200 mg) within a week of starting treatment, and effects on inattention and hyperactivity as factors that should differentiate the drug against rival non-stimulant ADHD drugs.

"We feel extremely good about the effect size we have demonstrated … and more importantly about the consistency and tight range for the effect size across all our phase II and III studies," he said, noting that in Strattera studies there was a wide and unpredictable effect in trials, and it is necessary to wait for four or five weeks to gauge its effect.

"The data provides a very strong differentiating point to other products on the market," he insisted, noting that SPN-812 should also avoid warnings on liver or cardiovascular toxicity, which are present on Strattera’s labelling.

Viloxazine has been sold as an antidepressant in a number of markets so has plenty of clinical experience but was never launched in the US and Supernus will have five years of market exclusivity if it is approved by the FDA.

Supernus has been guiding on a 3% to 5% market share for SPN-812 in the market – which is estimated to be worth several billion dollars a year – although Khattar told analysts he felt those predictions might be conservative given the data from its first two phase III studies. Based on the new data, Mizuho Securities has suggested sales could reach $600 million in 2025.

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