Colistimethate Sodium For Injection IP 2000000 IU is an antibiotic that fights bacteria. It is used to treat severe bacterial infections of the body. It is commonly used for critically ill patients admitted to the hospital. Colistimethate Sodium For Injection IP 2000000 IU is used to treat certain infections caused by bacteria. Colistimethate injection is in a class of medications called antibiotics. It works by killing bacteria. Antibiotics such as colistimethate injection will not work for colds, flu, or other viral infections.