Antibiotics are only effective against bacteria and not against viruses. The common cold, the flu, and acute otitis media are usually viral infections. Hence, antibiotics do not work in these cases.
The following fact boxes will help you weigh the benefits and harms of antibiotics.
Note on the Use of Antibiotics
An overuse of antibiotics can lead to antibiotic resistance. Antibiotic resistance means that antibiotics lose their ability to kill bacteria or inhibit their growth. Acquired resistance, which occurs through genetic changes to bacteria, is problematic because it reduces the effectiveness of antibiotic treatment.