Alkermes PLC jumped after the company said its treatment for schizophrenia continued to show effectiveness in a midstage study, with patients showing significantly less weight gain, on average, than those using olanzapine, an established antipsychotic drug. The biopharmaceutical plans to request a meeting with US regulators to move its treatment, ALKS 3831, into a late-stage study this year. Alkermes, based in Ireland but with a large campus in Waltham, estimates the treatment could hit the market in 2019.