Acorda Therapeutics (ACOR): Ampyra gets FDA approval

The FDA approved Acorda’s Ampyra (4-aminopyridine, 4-AP, fampridine-SR, dalfampridine) to improve walking speed for MS patients.   The 10 mg sustained release drug uses drug delivery technology developed by Elan (ELN) and is taken twice daily.   A risk mitigation strategy will be utilized to educate about the risk of seizures, which ocurred in less than 1% of patients in the phase III studies.  Unlike the immunomodulators, the drug can be used for patients with any type of MS who have leg weakness.   Primary progressive MS and non-relapsing secondary progresive MS will likely use the drug in monotherapy.  Those with realpsing remitting or relapsing sencondary progressive MS will be more likely to add the medication onto existing immunomodulatory therapy.   4-AP acts through a voltage gated potassium channel to prolong the action potential leading to improved conduction through demyelinated and poorly remyelinated axons and increasing the release of acetylcholine at the neuromuscular junction.   It has been shown to improve walking speeds in a subset of patients with multiple sclerosis. 

 

Patients with mild and moderate weakness are more likely to benefit than those with severe weakness or those with severe spasticity.  Many MS patients have no significant weakness.  Thus, one may assume that about 50% of MS patients are potential candidates for treatment.  In the trials, 35% of subjects with MS significantly benefited.  Hence, 17% of MS patients could potentially become long-term users of the drug.  Of course, penetration will be lower as some patients will have side effects, some will decide not to continue on therapy and some will never start due to fear of seizure.   Twice daily dosing will have minimal impact.  Others will not start due to cost, insurance barriers or be under management from a conservative physician.  Taking all this into account, I would expect a peak use of 7 – 9 % of all MS patients in the US, Canada, EU, Australia/NZ and Japan (1.2 to 1.5 million total patients).    This would be in the 90,000 – 135,000 patient range.   There will be minimal off label use for Lambert Eaton myasthenic syndrome, some neuropathies and possibly mild spinal cord injuries. 

 

The drug will likely be priced around $8000/yr.   Complicating the calculation, Biogen Idec (BIIB) has the rights to the drug outside the US.  4-aminopyridine is very inexpensive.  However, with 16% royalties to Elan, marketing expenses, and other overhead, the ultimate margin may average about 30-40% at steady-state but be far lower initially.  Hence, when steady state is reached in 4 years, profitability should be about 200-300 million (2500/yr x 100,000 patients).     There is no other agent to offer short-term competition, though 3, 4 diaminopyridine has a similar profile and is in clinical trials.