Your head throbs, your nose is stuffy, and you're too tired to do anything but flop into bed at the end of the day. You're probably coming down with a cold or the flu. But if you think that antibiotics will help you feel better, think again. Antibiotics won't do a thing for viral illnesses such as colds, flu and most sore throats. What's more, taking antibiotics when you don't need them actually can be harmful. Here's more information on what antibiotics are, when they should and shouldn't be used, and what you can do to combat antibiotic resistance.

Antibiotics are powerful drugs used for treating many serious and life-threatening infectious diseases. Most infections result from either bacteria or viruses.

Bacteria are responsible for:

• Many ear infections
• Some sinus infections
• Strep throat
• Urinary tract infections
• Many wound and skin infections

Viruses are responsible for:

• Colds
• Influenza
• Most sore throats
• Most coughs

Antibiotics can help you get better if a bacterial infection is responsible for your illness, but they'll have no effect if you have a virus. Taking antibiotics when you don't need them can lead to germs that are antibiotic-resistant — one of the gravest threats to public health worldwide.

The first antibiotic, penicillin, was introduced in the 1940s. Since then, scientists have developed more than 150 of these drugs to help stop the spread of infectious disease. But although these drugs have saved millions of lives, they also have a dark side — their frequent use has given rise to bacteria that are resistant to most, if not all, commonly used antibiotics.

Superbugs emerge when an antibiotic fails to kill every all of the bacteria it targets, and the surviving bacteria become resistant to that particular drug. Doctors then prescribe a stronger antibiotic, but the bacteria quickly learn to withstand the more potent drug as well, perpetuating a cycle in which increasingly powerful drugs are required to treat infections. Superbugs also can exchange survival information with other bacteria — even different species — allowing additional drug-resistant organisms to emerge.

For years, the potent antibiotic vancomycin (Vancocin) was a reliable last defense against certain severe infections, notably those caused by staphylococcus and enterococcus bacteria. But in recent years, some superbugs have figured out how to resist vancomycin; a strain of vancomycin-resistant enterococci (VRE) first appeared in the late 1980s and has thrived ever since. Scientists worry that VRE not only will continue to multiply but will share its genetic secrets for survival with other bacteria.

When more and more bacteria become resistant to first-line treatments, the consequences are severe. Illnesses last longer, and the risk of complications and death increases. In the United States alone, nearly 100,000 people die each year from infections they contract in the hospital, often because the bacteria that cause hospital-acquired infections are resistant to antibiotics. The inability to treat a particular infection leads to longer periods in which a person is contagious and able to spread the resistant strains to others.

The failure of first-line treatments also means that doctors have to resort to less- conventional medications, many of which are much more costly and more toxic than common drugs are. For instance, the drugs needed to treat multidrug-resistant forms of tuberculosis (TB) are 100 times more expensive than the drugs used to treat nonresistant TB. The course of treatment is long — up to two years — and the side effects can be severe.

Other consequences are the increased costs associated with prolonged illnesses, including the direct expense for additional laboratory tests, treatments and hospitalization, and the indirect costs from loss of income or time away from family.

Frequent and unnecessary antibiotic use accounts for most of the increase in resistant bacteria. Here are some things you can do to promote proper use of antibiotics:

• Understand when antibiotics should be used. Don't expect to take antibiotics every time you're sick. Antibiotics are effective in treating most bacterial infections, but they're not useful against viral infections, such as colds or the flu. Each year in the United States, doctors write an estimated 50 million antibiotic prescriptions for viral illnesses for which antibiotics offer no benefit. And even some common bacterial ailments, such as bronchitis, don't respond well to antibiotics.
• Take antibiotics exactly as prescribed. Follow your doctor's instructions when taking prescribed medication, including how many times a day and for how long. Avoid stopping treatment a few days early if you start feeling better — a complete course of antibiotics is needed to kill all of the harmful bacteria. A shortened course of antibiotics, on the other hand, often wipes out only the most vulnerable bacteria, while allowing relatively resistant bacteria to survive.
• Never take antibiotics without a prescription. If you didn't complete a full course of antibiotics, you might be tempted to use the leftover medication the next time you get sick or to pass it along to someone else. But this is never a good idea. For one thing, the antibiotic might not be appropriate for your own or another person's illness. And even if it is, you're not likely to have enough pills to combat the germs making you sick, which can lead to more resistant bacteria.
• Don't pressure your doctor for antibiotics if you have a viral illness. Instead, talk with your doctor about ways to relieve the symptoms of your viral illness — a saline nasal spray to clear a stuffy nose, for instance, or a mixture of warm water, lemon and honey to temporarily soothe a sore throat.
• Protect yourself from infection in the first place. You can keep many germs at bay by adopting preventive habits, such as washing your hands thoroughly and often, handling and preparing food safely, and keeping up-to-date on immunizations.

When you abuse antibiotics, the resistant microorganisms that you help create can become widely established, causing new and hard-to-treat infections. That's why the decisions you make about antibiotic use — unlike almost any other medicine you take — extend far beyond your reach. Responsible antibiotic use protects the health of your family, neighbors and ultimately the global community.