Xenon Pharmaceuticals Inc. CEO Simon Pimstone said it's going to be hard to ultimately define the reason that the firm's sodium channel Nav1.7 inhibitor, TV-45070, failed to outperform placebo in a phase II postherpetic neuralgia (PHN) trial, but that "if the drug is not fully engaging the targets at the right sites, it doesn't really matter: there's not going to be an effect."