Powerful antibiotic drugs are normally injected once a day—a problem for patients who contract infections in hospital wards and are sent home. But a new study found that an experimental antibiotic may work just as well when given in one gigantic dose, marking progress in the treatment of drug-resistant infections, including MRSA. The research was conducted by Targanta Therapeutics Corp., a company that has applied to sell the antibiotic, oritavancin, in the U.S.