Gemifloxacin It works by stopping the growth of bacteria. This antibiotic treats only bacterial infections. It will not work for viral infections (such as common cold, flu). Using any antibiotic when it is not needed can cause it to not work for future infections. Gemifloxacin is used to treat bronchitis and pneumonia caused by bacterial infections. Gemifloxacin belongs to the class of medicines known as quinolone antibiotics. It works by killing bacteria or preventing their growth. However, this medicine will not work for colds, flu, or other virus infections.