Initial efforts at Humanigen Inc. to win an FDA emergency use authorization (EUA) for treating hospitalized COVID-19 patients with its monoclonal antibody, lenzilumab, have failed to gain the regulator's buy-in, sending company shares (NASDAQ:HGEN) down 47.3% to $7.97 on Sept. 9 after touching a 52-week low during the session, a reaction part of a volatile arc that has seen shares climb as high as $29.20 during the same time span.