July 20 (Reuters) - Alnylam Pharmaceuticals (ALNY.O) and Cubist Pharmaceuticals (CBST.O) said a mid-stage study of their experimental drug for a respiratory infection met the main goal. The companies, which had reported promising results from mid-stage studies last month, said the inhaled drug, ALN-RSV01, met the main goal of safety and tolerability in the phase 2 study.