** Shares of drugmaker Arrowhead Pharmaceuticals ARWR.O rise 18.1% to $88 premarket

** Co says its approved RNA-based drug plozasiran met the main and all secondary goals in two late-stage trials testing it in a broader group of patients with severely high triglycerides, a type of fat in the blood

** The drug, branded as Redemplo, reduced triglyceride levels by 79% and 81% after 12 months in the two studies, versus about 27% for placebo

** Plozasiran also cut cases of acute pancreatitis, a potentially fatal inflammation of the pancreas, by 78% across the studies and prevented all such events among the highest-risk patients - ARWR

** Co says no new safety concerns were seen and plans to seek expanded U.S. approval by year-end; detailed results are due on Aug. 30

** As of last close, ARWR up 12.3% YTD