Antibiotics are medications that are used to prevent and treat bacterial infections. Different antibiotics are used for different sorts of bacteria. Some antibiotics work only against a very small group of bacteria types, while others are effective against a broad spectrum of different bacteria. Generally, doctors try to use the most specific antibiotic they can to treat an infection, to minimize side effects.

A common misconception about antibiotics is that they are always needed after surgery to prevent infection or help wounds heal. While antibiotics are commonly given in the operating room right before an operation starts, the reality is that in almost all cases, antibiotics are not needed after the operation. While appropriate use of antibiotics is an important part of surgery, overuse of antibiotics, using overly broad-acting antibiotics, or using the wrong antibiotic can lead to serious complications. For a somewhat technical, but still readable, description of when antibiotics are indicated for surgery, see this article.

A large number of scientific studies have been done to try to figure out the best antibiotics to use and the best time to use them. The data can be a bit confusing, but there are some basic principles that are well agreed upon:

Before Your Operation

For planned operations, wound infections can be reduced by washing with an antibacterial soap such as chlorhexidine before surgery. Often your doctor will provide you with a bottle of this soap to use when you shower the night before or day of your operation. There is no need to take antibiotic pills before you have an operation.

At the Time of Your Operation

Just before your operation begins, a member of the surgical team will clean your skin with an antimicrobial scrub solution. Although it’s not possible to make the skin completely sterile, enough bacteria are eliminated by the scrub that wound infections are uncommon even when a patient does not receive intravenous (IV) antibiotics. For some simple operations with little risk of infection, such as minor skin surgery, a surgical scrub may be enough and IV antibiotics may not be necessary. For the most part, any operation that involves going deeper than the skin requires IV preoperative antibiotics.

If antibiotics are indicated, your anesthesiologist will give a dose of IV antibiotics shortly before the operation begins. The exact antibiotic used depends on the operation. Usually, an antibiotic that’s fairly specific to the bacteria found on the skin is used. This is because the inside of the body is mostly sterile — the big exception being the gastrointestinal tract — so the only bacteria likely to cause an infection are from the skin. For operations on the gastrointestinal tract, broader spectrum antibiotics are used. Many of these antibiotics are similar to penicillin or sulfa drugs, which many people are allergic to, so be sure to tell your medical team if you have any drug allergies.

After Your Operation

Antibiotic use after an operation is the area with the most controversy. While most people do not benefit from antibiotics after the operation is complete, there are some cases where antibiotics after an operation is indicated. Examples include an operation for an abdomen infection or an operation in which an artificial implant is inserted.

Why Not Use Antibiotics?

A common question from patients is why not take antibiotics, just to be safe? Unfortunately, antibiotics bring with them lots of potential problems. These are important to know about:

• Allergies: Antibiotics, like most medications, can cause allergic reactions, ranging from bothersome to very serious.

• Side effects: Diarrhea, nausea, and rashes are the most common antibiotic side effects, but more lasting damage, including damage to the liver and kidneys, can also occur.

• Resistance: Antibiotics don’t kill all bacteria, and the ones that survive can develop resistance to the drug, making it harder to fight infections, and even putting family, friends, and the community at risk. The most well-known example of antibiotic resistance is the MRSA (Methicillin-resistant Staphylococcus aureus) bacteria, where normally susceptible Staphylococcus bacteria became resistant to common antibiotics and can now only be treated with high-powered, sometimes toxic, antibiotics.

• Infections not treated with antibiotics: Infections can only be treated by antibiotics if the antibiotics can reach the infection through the blood stream. So infections that don’t get good blood flow, such as infected fluid collections or abscesses, may need surgical drainage rather than antibiotic therapy. Likewise, infections that are treated with surgery may not need antibiotics.

• Elimination of good bacteria: Some bacteria in your body play important roles in keeping you healthy. This is especially true in your intestine, where some “good” bacteria help to break down food and to protect your body from “bad” bacteria. Antibiotics can eliminate these good bacteria, which can lead to digestive problems and to overgrowth of bad bacteria – especially a bacteria called Clostridium difficile or C. diff. C. diff infections can be a serious problem, requiring weeks of antibiotic therapy or even emergency surgery to remove the infected bowel.

Want to know more? The CDC has put together a nice web page containing many links to good resources about surgical site infections, including information about pre-operative antibiotics.

This story originally appeared in the  Health Dialog Care Compass Blog.