Praxis Precision Medicines has recorded a midphase win in epilepsy, linking the high dose of PRAX-628 to a 100% complete response rate to clear the path for a larger study in the second half of the year.
The phase 2a trial tested the sodium-channel drug candidate in epilepsy patients with photoparoxysmal response (PPR), a form of photosensitivity. Patients needed to have demonstrated PPR during screening to be evaluated in the trial. After treatment with PRAX-628, Praxis saw a 100% complete response rate in the high, 45mg cohort. The complete response rate on the lower dose was 80%.
Shares in Praxis rose 25% to almost $64 in the opening hours of trading on Tuesday from a Monday closing price of $50.58.
On a conference call with investors to discuss the results, Dan Friedman, M.D., professor of neurology at NYU Grossman School of Medicine, said the photoparoxysmal model is very useful for first-in-patient studies because “it has predictive ability for drugs that are ultimately efficacious in the clinic, especially those with broad spectrum activity.” Friedman cited cenobamate, brivaracetam and levetiracetam as molecules that suppressed PPR and were then shown to be efficacious.
Yet, it is unclear exactly what the effect on PPR means for the prospects of PRAX-628. Friedman said the field lacks “a really good relationship between the degree of suppression we see in these relatively small studies with a heterogeneous group of patients with a specific type of epilepsy, usually a generalized epilepsy, and ultimate efficacy in the clinic.”
Praxis wants to answer the question of what efficacy PRAX-628 will ultimately achieve and is planning to start a study in focal epilepsy in the second half of the year.
“There are about 30% excess patients there when you count for focal, so we’re growing the available pool by at least 30%,” Praxis CEO Marcio Souza explained on the call. “That is a fair bit of upside. We are now running the numbers … to look into how we can accelerate towards that indication as well. We’re looking forward to getting a development program that can cover not only focal, but also generalized as well.”