Buy the Book

Print This Topic Email This Topic

Pronunciations aminoglycosides anaphylaxis arrhythmia aztreonam cephalosporins chloramphenicol clindamycin coccal colitis endocarditis Escherichia coli ethambutol gastrointestinal gonorrhea imipenem isoniazid Klebsiella macrolide meningitis metronidazole myasthenia gravis myelitis neuropathy nitrofurantoin osteomyelitis pneumonia polyp prophylaxis prostatitis Pseudomonas pyrazinamide quinolones rickettsial rifampin salmonella sepsis serotonin spectinomycin staphylococcal sulfasalazine sulfonamides vancomycin warfarin

• Although doctors try to use antibiotics for specific bacterial infections, they sometimes start antibiotics without waiting for tests that identify the specific bacteria.
• Bacteria can develop resistance to the effects of antibiotics.
• Taking antibiotics as directed, even after symptoms disappear, is essential to curing the infection and to preventing the development of resistance in bacteria.
• Antibiotics can have side effects, such as upset stomach, diarrhea, and, in women, vaginal yeast infections.
• Some people are allergic to certain antibiotics.

Antibiotics (antibacterials) are drugs derived wholly or partially from bacteria or molds and are used to treat bacterial infections. They are ineffective against viral (see Fungal Infections: Risk Factors for Developing Fungal Infections) and fungal infections (see Viral Infections: Antiviral Drugs). Antibiotics either kill microorganisms or stop them from reproducing, allowing the body's natural defenses to eliminate them.

Selecting an Antibiotic

Each antibiotic is effective only against certain bacteria. In selecting an antibiotic to treat a person with an infection, doctors estimate which bacteria are likely to be the cause. For example, some infections are caused only by certain types of bacteria. If one antibiotic is predictably effective against all of these bacteria, further testing is not needed. If infections may be caused by many different types of bacteria or by bacteria that are not predictably susceptible to antibiotics, a laboratory is asked to identify the infecting bacteria from samples of blood, urine, or tissue taken from the person (see Biology of Infectious Disease: Biological Warfare and Terrorism). The infecting bacteria are then tested for susceptibility to a variety of antibiotics. Results of these tests usually take a day or two and thus cannot guide the initial choice of antibiotic.

Antibiotics that are effective in the laboratory do not necessarily work in an infected person. The effectiveness of the treatment depends on how well the drug is absorbed into the bloodstream, how much of the drug reaches the sites of infection in the body, and how quickly the body eliminates the drug. These factors may vary from person to person, depending on other drugs being taken, other disorders present, and the person's age. In selecting an antibiotic, doctors also consider the nature and seriousness of the infection, the drug's possible side effects, the possibility of allergies or other serious reactions to the drug, and the cost of the drug.

Combinations of antibiotics are sometimes needed to treat the following:

• Severe infections, particularly during the first days when the bacteria's susceptibility to antibiotics is not known
• Certain infections caused by bacteria that rapidly develop resistance to a single antibiotic
• Infections caused by more than one type of bacteria if each type is susceptible to a different antibiotic

Antibiotics Drug Common Uses Side Effects Aminoglycosides Amikacin Some Trade Names AMIKIN Gentamicin Some Trade Names GARAMYCIN Kanamycin Some Trade Names KANTREX Neomycin Netilmicin Some Trade Names NETROMYCIN Streptomycin Tobramycin Some Trade Names NEBCIN TOBREX Infections caused by gram-negative bacteria, such as Escherichia coli and Klebsiella species Hearing loss Dizziness Kidney damage Carbapenems Ertapenem Some Trade Names INVANZ Doripenem Imipenem-cilastatin Some Trade Names PRIMAXIN Meropenem Some Trade Names MERREM Gangrene, sepsis, pneumonia, abdominal and urinary infections, infections due to susceptible bacteria resistant to other antibiotics, and (except for ertapenem Some Trade Names INVANZ ) Pseudomonas infections Seizures (especially with imipenem) Confusion Cephalosporins, 1st generation Cefadroxil Some Trade Names DURICEF Cefazolin Some Trade Names ANCEF KEFZOL ZOLICEF Cephalexin Some Trade Names KEFLEX Mainly skin and soft-tissue infections Gastrointestinal upset and diarrhea Nausea Allergic reactions Cephalosporins, 2nd generation Cefaclor Some Trade Names CECLOR Cefoxitin Some Trade Names MEFOXIN Cefprozil Some Trade Names CEFZIL Cefuroxime Some Trade Names CEFTIN ZINACEF Loracarbef Some Trade Names LORABID Some respiratory and, for cefoxitin Some Trade Names MEFOXIN , abdominal infectionss Gastrointestinal upset and diarrhea Nausea Allergic reactions Cephalosporins, 3rd generation Cefixime Some Trade Names SUPRAX Cefdinir Some Trade Names OMNICEF Cefditoren Some Trade Names SPECTRACEF Cefoperazone Some Trade Names CEFOBID Cefotaxime Some Trade Names CLAFORAN Cefpodoxime Some Trade Names VANTIN Ceftazidime Some Trade Names FORTAZ TAZICEF TAZIDIME Ceftibuten Some Trade Names CEDAX Ceftizoxime Some Trade Names CEFIZOX Ceftriaxone Some Trade Names ROCEPHIN Given by mouth: Broad coverage of many bacteria for people with mild-to-moderate infections, including skin and soft-tissue infections Given by injection: Serious infections (such as meningitis or infections acquired in a hospital) Gastrointestinal upset and diarrhea Nausea Allergic reactions Cephalosporins, 4th generation Cefepime Some Trade Names MAXIPIME Serious infections (including Pseudomonas infections), particularly in people with a weakened immune system and infections due to susceptible bacteria resistant to other antibiotics Gastrointestinal upset and diarrhea Nausea Allergic reactions Cephalosporins, 5th generation Ceftobiprole Complicated skin infections, including foot infections in people with diabetes, due to susceptible bacteria, such as Escherichia coli, Pseudomonas aeruginosa, and methicillin-resistant Staphylococcus aureus (MRSA)   Fluoroquinolones Ciprofloxacin Some Trade Names CILOXAN CIPRO Levofloxacin Some Trade Names QUIXIN LEVAQUIN Lomefloxacin Some Trade Names MAXAQUIN Moxifloxacin Some Trade Names AVELOX Norfloxacin Some Trade Names NOROXIN Ofloxacin Some Trade Names FLOXIN OCUFLOX Trovafloxacin Some Trade Names TROVAN Sepsis, urinary tract infections, bacterial prostatitis, bacterial diarrhea, and gonorrhea Nausea (rare) Nervousness, tremors, and seizures Inflammation or rupture of tendons Abnormal heart rhythms (arrhythmias) Antibiotic-associated diarrhea and inflammation of the colon (colitis) With trovafloxacin Some Trade Names TROVAN , sometimes fatal liver damage Glycylcycline Tigecycline Complicated abdominal infections and complicated skin infections due to susceptible bacteria, such as Escherichia coli, Staphylococcus aureus (including those resistant to methicillin Some Trade Names STAPHCILLIN ), and anaerobes Gastrointestinal upset Sensitivity to sunlight Permanent staining of teeth in the fetus if used late in pregnancy or in children under 8 years of age Macrolides Azithromycin Some Trade Names ZITHROMAX Clarithromycin Some Trade Names BIAXIN Dirithromycin Some Trade Names DYNABAC Erythromycin Some Trade Names E-MYCIN ERYTHROCIN ILOSONE Troleandomycin Some Trade Names TAO Streptococcal infections, syphilis, respiratory infections, mycoplasmal infections, and Lyme disease Nausea, vomiting, and diarrhea (especially at higher doses) Jaundice Abnormal heart rhythms Monobactam Aztreonam Some Trade Names AZACTAM Infections caused by gram-negative bacteria Allergic reactions Can be used in patients allergic to antibiotics such as penicillins, cephalosporins, and carbapenems Penicillins Amoxicillin Some Trade Names AMOXIL POLYMOX TRIMOX Ampicillin Some Trade Names OMNIPEN POLYCILLIN PRINCIPEN Carbenicillin Some Trade Names GEOCILLIN Cloxacillin Some Trade Names TEGOPEN Dicloxacillin Some Trade Names DYCILL DYNAPEN PATHOCIL Nafcillin Some Trade Names UNIPEN Oxacillin Some Trade Names PROSTAPHLIN Penicillin G Penicillin V Some Trade Names PEN-VEEK VEETIDS Piperacillin Some Trade Names PIPRACIL Ticarcillin Some Trade Names TICAR Wide range of infections, including streptococcal infections, syphilis, and Lyme disease Nausea, vomiting, and diarrhea Allergy with serious anaphylactic reactions Brain and kidney damage (rare) Polypeptides* Bacitracin Some Trade Names AK-TRACIN Colistin Some Trade Names COLY-MYCIN Polymyxin B Ear, eye, skin, or bladder infections Usually applied directly to the skin, and rarely given by injection Kidney and nerve damage (when given by injection) Sulfonamides Mafenide Some Trade Names SULFAMYLON Sulfacetamide Some Trade Names BLEPH-10 SULAMYD Sulfamethizole Sulfasalazine Some Trade Names AZULFIDINE Sulfisoxazole Some Trade Names GANTRISIN Trimethoprim-sulfamethoxazole Some Trade Names BACTRIM SEPTRA Urinary tract infections (except sulfasalazine Some Trade Names AZULFIDINE , sulfacetamide Some Trade Names BLEPH-10 SULAMYD , and mafenide Some Trade Names SULFAMYLON ) For mafenide Some Trade Names SULFAMYLON only topically for burns Nausea, vomiting, and diarrhea Allergy (including skin rashes) Crystals in urine (rare) Decrease in white blood cell and platelet counts Sensitivity to sunlight Possibly increased tendency to bleed if used along with warfarin Some Trade Names COUMADIN Tetracyclines Demeclocycline Some Trade Names DECLOMYCIN Doxycycline Some Trade Names VIBRAMYCIN Minocycline Some Trade Names MINOCIN Oxytetracycline Some Trade Names TERRAMYCIN Tetracycline Some Trade Names ACHROMYCIN V TETRACYN SUMYCIN Syphilis, chlamydial infections, Lyme disease, mycoplasmal infections, and rickettsial infections Gastrointestinal upset Sensitivity to sunlight Staining of teeth in children under 8 years old or in the fetus if used late in pregnancy Miscellaneous antibiotics Chloramphenicol Some Trade Names CHLOROMYCETIN Typhoid, other salmonellal infections, and meningitis Severe decrease in white blood cell count (rare) Clindamycin Some Trade Names CLEOCIN Streptococcal and staphylococcal infections, respiratory infections, and lung abscess Antibiotic-associated diarrhea and inflammation of the colon (colitis) Daptomycin Complicated skin infections, bloodstream infections, and certain heart valve infections (endocarditis) due to susceptible bacteria, including methicillin Some Trade Names STAPHCILLIN -resistant Staphylococcus aureus (MRSA) Not used when infection involves the lungs Gastrointestinal upset Muscle pain and weakness Ethambutol Some Trade Names MYAMBUTOL Tuberculosis Vision disturbances Fosfomycin Some Trade Names MONUROL Bladder infections Diarrhea Isoniazid Some Trade Names INH NYDRAZID Tuberculosis Nausea and vomiting Jaundice Linezolid Some Trade Names ZYVOX Serious infections caused by gram-positive bacteria that are resistant to many other antibiotics Nausea Headache Diarrhea Anemia and low white blood cell and platelet counts Numbness and tingling in the hands and feet (peripheral neuropathy) Visual disturbances Confusion, agitation, tremors or coma in some people who also use selective serotonin-release inhibitors (SSRIs) Metronidazole Some Trade Names FLAGYL Vaginitis caused by Trichomonas or Gardnerella species and pelvic and abdominal infections Nausea Headache (especially if the drug is taken with alcohol) Metallic taste Numbness and tingling in the hands and feet (peripheral neuropathy) Dark urine Nitrofurantoin Some Trade Names FURADANTIN MACRODANTIN Urinary tract infections Nausea and vomiting Allergy Pyrazinamide Tuberculosis Liver dysfunction Gout (occasionally) Quinupristin-dalfopristin Some Trade Names SYNERCID Serious infections caused by gram-positive bacteria that are resistant to other antibiotics Aching muscles and joints Rifampin Some Trade Names RIFADIN RIMACTANE Tuberculosis and leprosy Rash Liver dysfunction Red-orange saliva, sweat, tears, and urine Spectinomycin Some Trade Names TROBICIN Gonorrhea Allergy Fever Telithromycin Mild to moderate community-acquired pneumonia Visual disturbances Liver damage (possibly fatal) Worsening of symptoms in people with myasthenia gravis (possibly fatal) Vancomycin Some Trade Names VANCOCIN Serious infections, especially those due to MRSA or Enterococcus, and those resistant to other antibiotics Flushing, itching Allergic reactions Decrease in white blood cell and platelet counts *Polypeptide antibiotics are usually applied directly to the skin or eye and are rarely given by injection.

Antibiotic Resistance

Bacteria, like all living organisms, change over time in response to environmental challenges. Because of the widespread use and misuse of antibiotics, bacteria are constantly exposed to these drugs. Although many bacteria die when exposed to antibiotics, some develop resistance to the drugs' effects. For example, 50 years ago, Staphylococcus aureus (a common cause of skin infections) was very sensitive to penicillin. But over time, strains of this bacteria developed an enzyme able to break down penicillin, making the drug ineffective. Researchers responded by developing a form of penicillin that the enzyme could not break down, but after a few years, the bacteria adapted and became resistant to this modified penicillin. Other bacteria have also developed resistance to antibiotics.

Spotlight on Aging When doctors prescribe antibiotics for older people, they may start with a lower dose than usual because the kidneys tend to function less well as people age. In such cases, the kidneys may not be able to eliminate antibiotics from the body as effectively, increasing the risk of side effects. Doctors also consider the following: What other drugs the person is taking because older people tend to take many drugs and drug interactions are a risk Whether the antibiotic regimen is complex and hard to follow Whether the person has family members or caregivers who can help the person take the antibiotic as prescribed Whether the person lives in a nursing home because different bacteria may cause infections in such situations

Medical research continues to develop drugs to combat bacteria. But patients and doctors can help prevent the development of resistance in bacteria (see Antibiotics: Antibiotic Resistance). Taking antibiotics only when necessary can help. That is, people should take antibiotics only for infections caused by bacteria, not for those caused by viruses such as a cold or the flu. Also, taking antibiotics for the complete time prescribed helps limit the development of resistance.

Taking Antibiotics

For severe bacterial infections, antibiotics are usually first given by injection (usually into a vein but sometimes into a muscle). When the infection is controlled, antibiotics can then be taken by mouth. For less severe infections, antibiotics can be given by mouth from the start.

Antibiotics need to be taken until the infecting bacteria are eliminated from the body, which may be days after the symptoms disappear. So people must take them for the entire time prescribed whether they have symptoms or not. Antibiotics are rarely given for fewer than 5 days. (An exception is certain uncomplicated urinary tract infections.) Stopping treatment too soon can result in a return of the infection or the development of antibiotic-resistant bacteria.

Did You Know... If a virus is causing the infection, taking antibiotics is useless and can contribute to the development of resistance in bacteria.

A doctor, nurse, or pharmacist can explain how the prescribed antibiotic should be taken and what side effects it may have. Some antibiotics must be taken on an empty stomach. Others may be taken with food. Metronidazole Some Trade Names
FLAGYL
, a common antibiotic, causes an unpleasant reaction with alcohol. Also, some antibiotics can interact with other drugs people may be taking, possibly reducing the effectiveness or increasing the side effects of the antibiotic or the other drugs. Some antibiotics make the skin sensitive to sunlight.

Antibiotics are sometimes used to prevent infections (called prophylaxis). Antibiotics may be given to people who have been exposed to a person with meningitis to prevent meningitis from developing. Some people with abnormal or artificial heart valves take antibiotics before dental and surgical procedures to prevent bacteria from infecting the damaged or artificial valves (such procedures can allow bacteria to enter the body). People undergoing surgery with a high risk of introducing infection (such as major orthopedic or intestinal surgery) may be given antibiotics immediately before the operation. To be effective and to avoid the development of resistance in bacteria, preventive antibiotics are used for only a short time. Antibiotics may also be given to people who have a weakened immune system, such as people with leukemia, people taking chemotherapy for cancer, or people with AIDS, because such people are particularly susceptible to serious infections. They may need to take the antibiotics for a long time.

Home Antibiotic Therapy

Usually, antibiotics are given by mouth, and the length of treatment does not cause hardship. However, some infections—such as those involving bone (osteomyelitis) or the heart (endocarditis)—require antibiotics to be given intravenously for a long time, often 4 to 6 weeks. If people have no other conditions that need treatment in the hospital and are feeling relatively well, intravenous (IV) antibiotics may be given at home. When antibiotics have to be given a long time, the short IV catheters that are inserted into a small vein in the arm or hand (such as are used in most routine hospital procedures) may not be desirable. These catheters last only up to 3 days. Instead, a special type of IV catheter may be inserted into a large central vein, usually in the neck or chest.

Some devices for infusing antibiotics are simple enough that people and their family members can learn to operate them on their own. In other cases, a visiting nurse must come to the home to give each dose. In either situation, people are carefully supervised to make sure the antibiotic is being given correctly and to watch for possible complications and side effects.

If antibiotics are given at home through an IV catheter, the risk of developing an infection at the site where the catheter is inserted and in the bloodstream is increased. Pain, redness, and pus at the catheter insertion site or chills and fever (even without problems at the insertion site) may indicate a catheter-related infection.

Side Effects and Allergic Reactions

Common side effects of antibiotics include upset stomach, diarrhea, and, in women, vaginal yeast infections. Some side effects are more severe and, depending on the antibiotic, may impair the function of the kidneys, liver, bone marrow, or other organs. Blood tests are sometimes used to check for effects on kidney and other organ function.

Some people who take antibiotics, especially cephalosporins, clindamycin Some Trade Names
CLEOCIN
, or fluoroquinolones, develop colitis, an inflammation of the large intestine. This type of colitis results from a toxin produced by the bacteria Clostridium difficile, which is resistant to many antibiotics and which grows in the intestines unchecked when other normal bacteria in the intestine are killed by the antibiotics (see Clostridium difficile–Induced Colitis).

Antibiotics can also cause allergic reactions. Mild allergic reactions consist of an itchy rash or slight wheezing. Severe allergic reactions (anaphylaxis) can be life-threatening and usually include swelling of the throat, inability to breathe, and low blood pressure.

Many people tell their doctor that they are allergic to an antibiotic when they have only experienced side effects that are not allergy-related. The distinction is important because people who are allergic to an antibiotic should not be given that drug or an antibiotic closely related to it. However, people who have experienced minor side effects can usually take related drugs or even continue taking the same one. Doctors can determine the significance of any unpleasant reaction people have to an antibiotic.

Last full review/revision September 2008 by Matthew E. Levison, MD