Catalyst's shares have been on a roller-coaster ride ever since the FDA approved Ruzurgi, and for good reason. Although this rival LEMS medication is approved only for patients between the ages of 6 to 17 years, it could, in theory, be prescribed for off-label use by adults, which means it poses a significant competitive threat to Catalyst's LEMS drug, Firdapse. Firdapse was launched as a treatment for adult LEMS patients last January, and it quickly grabbed the lion's share of the market.