It’s a common misconception that antibiotics work for any and all illnesses. Antibiotics are only effective against infections caused by bacteria. They do not work on colds or the flu because these illnesses are caused by viruses, not bacteria. Antiviral medicines are sometimes prescribed to treat influenza, better known as the flu. Most cases of the flu and colds get better on their own, without medication.
Bacteria and viruses have several important differences. Bacteria are microscopic, living germs that can cause an array of human infections. They cause disease by invading your body tissues, and then growing and multiplying. Some disease-causing bacteria also produce toxins, which contribute to the harm they cause in the body. Common bacterial infections include strep throat, urinary tract infections and pneumonia. If you contract one of these illnesses, your doctor will likely prescribe an antibiotic to kill the bacteria causing the infection.
Viruses cause infections in a completely different way than bacteria do. Viruses -- including those that cause colds and the flu -- use your own cells against you by taking them over and using their internal machinery to make more viruses. This causes the invaded cells to burst and die, releasing new viruses to infect other cells. Antibiotics are not effective at killing viruses or disrupting this cycle of invasion.
Although not as commonly used as antibiotics, antiviral medications are effective for treating or controlling some viral infections, such HIV, hepatitis C and influenza. Antiviral medications are not routinely used to treat the flu.
Cold and Flu Treatment
Because antibiotics are not effective for colds or the flu, treatment is usually limited to relieving the symptoms. These treatments do not kill the viruses but can make you more comfortable until the illness runs its course and your body gets rid of the viral infection on its own. For example, an over-the-counter decongestant can soothe symptoms such as a runny nose, while a fever-reducer -- such as acetaminophen (Tylenol) or ibuprofen (Motrin, Advil) -- can alleviate fever and chills.
Antiviral drugs are sometimes used to treat people who are hospitalized with the flu or have a high risk of flu complications, including people with certain health problems, children younger than age 2, adults older than 65 and pregnant women. Antivirals approved by the U.S. Food and Drug Administration for the treatment of season influenza include zanamivir (Relenza) and oseltamivir (Tamiflu).
When to Get Help
Although most people with a cold or the flu recover without medical attention -- and without antibiotics -- complications can develop with these viral illnesses, especially from influenza. Call your doctor for a fever of 100.4 F or higher in a child younger than 3 months, or 104 F in an older child. If you or your child experience shortness of breath, call your doctor right away.
Pregnant women, adults older than 65 and people with a weakened immune system or chronic illness should also call their doctor right away if symptoms of the flu develop. Antiviral therapy is most effective if started within the first 48 hours after the onset of flu symptoms.