Piper Jaffray analyst David Amsellem says that while his survey of 25 neurologists did not necessarily suggest that Supernus Pharmaceuticals' (SUPN) migraine prophylaxis treatment Trokendi XR will see pressure due to the availability of Amgen's (AMGN) Aimovig, there were data points that suggest Trokendi's volume growth "could slow meaningfully. 64% of respondents have patients with either moderate or significant difficulty with insurance coverage when trying to get a Trokendi XR prescription filled, Amsellem tells investors in a research note. He sees a "more tepid sales growth trajectory" for Trokendi XR going forward and reiterates a Neutral rating on Supernus with a $47 price target.