A post-marketing trial assessing a lower dose of Acorda's multiple sclerosis drug Ampyra has failed to meet its efficacy targets, but shares in the group were on the rise as the result actually leaves the drug with greater intellectual protection.

Ampyra (dalfampridine) is a potassium channel blocker approved in the US in 2010 as a treatment for improving walking in patients with MS.

However, the medicine can cause seizures, and as this risk increases the higher the dose, US regulators asked Acorda to investigate whether a 5mg twice daily version is as effective as the approved 10mg twice a day.

The four-week study randomised 430 participants to receive either placebo, or 5mg or 10mg of Ampyra twice daily. 

Unfortunately, neither dose of the Acorda's drug showed a stastically-significant improvement in the primary endpoint - change in walking speed - compared with the placebo arm.

But the company pointed out that the fact the approved 10mg dose failed to show a significant benefit was due to increased patient variability and study design.

Backing for 10mg dose

Moreover, it stressed that in a post-hoc analysis, data were analysed with "methods similar to those used in the pivotal studies", which indeed found that walking speed was significantly greater for the 10mg group compared to placebo.

“We believe the current study, together with the Ampyra registration studies, continue to show that 10mg twice daily is the appropriate, safe and effective dose," said Enrique Carrazana, Acorda’s chief medical officer. 

In addition no new safety signals were observed in this study, and no seizures were reported, the firm said.

Also pleasing shareholders, in a strange twist, had the 5mg version been effective, copycat forms of the drug could have entered the market as early as 2017, but the 10mg is protected by patents until 2027, according to Reuters. 

Last month, European regulators gave the drug - where it is sold by Biogen Idec as Fampyra - a conditional approval.