Antibiotics

A drug is a substance taken into the body that affects chemical reactions in the body. Antibiotics are drugs used to treat bacterial infections by killing bacteria.

Antibiotics do not affect viruses, so they cannot treat viral infections. An infection must be caused by bacteria for an antibiotic to be useful against it.

Some bacteria are resistant to an antibiotic: the antibiotic does not kill them effectively. If resistant bacteria cause an infection, that antibiotic may be less effective at treating it.