Antibiotics are a very important part of modern medicine. These drugs are used to fight many infections caused by bacteria. The following facts about antibiotics will help you understand how these drugs work, possible side effects, and the importance of taking antibiotics as directed by your doctor.

Antibiotics do not work against all infections.

Antibiotics work only against infections that are caused by bacteria. These drugs are not effective at all against most viral infections. This is why your doctor will not always prescribe an antibiotic if you have an infection.

Some antibiotics are effective against only certain types of bacteria; others can effectively fight a wide range of bacteria. Bacterial infections include strep throat, most (but not all) ear infections, and some sinus, bladder, and lung infections. Most common infections (such as colds, bronchitis and sore throats) are caused by viruses. Antibiotics should not be used for these viral infections because they don't help, they may cause side effects, and overuse of antibiotics contributes to the growing problem of bacterial resistance (see below). Some viral infections such as herpes infection, some cases of influenza, and HIV/AIDS can be treated with antiviral drugs. Based on your illness and symptoms (and laboratory tests, if necessary), your doctor can determine if prescribing an antibiotic is appropriate. Your doctor will then select the antibiotic that will work best for your infection.

Antibiotics may cause side effects.

If your doctor prescribes an antibiotic, be sure to ask him or her what possible side effects to watch for. Antibiotics can cause nausea, diarrhea and stomach pain. In some people, an allergic reaction (characterized by rash and itching; or in severe cases, difficulty breathing) can occur. Some antibiotics kill naturally occurring bacteria that are needed by the body; these "good" bacteria are then replaced by bacteria that can cause diarrhea or yeast infections. If you experience any side effects when you are taking an antibiotic, you should call your doctor.

Bacteria can become resistant to an antibiotic.

Bacteria can become resistant to an antibiotic that was previously effective. Resistance is most likely to develop after long-term treatment with an antibiotic or with antibiotics that kill a wide variety of bacteria. Resistance is a growing problem, and there is concern that some types of infections will eventually not be treatable with antibiotics. This resistance is ascribed to overuse of antibiotics, especially for common viral infections.

It is very important that antibiotics be taken as prescribed.

Antibiotics should only be used when prescribed by your doctor. Consult with your doctor before taking any other medications (including over-the-counter medications). You should never take antibiotics given to you by someone else or prescribed for a previous illness. Below are three basic guides to help ensure that your antibiotic treatment will be effective:

The dosage is a very important factor in antibiotic effectiveness.

If the dosage of the antibiotic is not adequate, it will not be effective for treatment of the infection and bacteria are more likely to develop resistance. This is because the bacteria can continue to grow and develop ways to disrupt the antibiotic's effects.

Antibiotics must be taken for the full amount of time prescribed by your doctor.

Many times, patients will stop the use of an antibiotic when they begin to feel better and it seems that the illness has gone. However, even after the symptoms are gone, the bacteria may still be present in small amounts and an infection can return if use of the antibiotic is stopped. Not completing the prescribed dose may also promote resistance.

Antibiotics should not be saved and reused.

You should always take the full course of antibiotic treatment, so none of the drug should be "left over." However, if this has occurred the antibiotics should not be taken to treat any other illness. Different types of infections require different types of antibiotics, so taking leftover medications is often not effective.

Always consult your doctor if you have an infection.