Saturday, January 28, 2012


-      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



Common Uses

Side Effects


Infections caused by gram-negative bacteria, such as Escherichia coli and Klebsiella species
Hearing loss
Kidney damage


Gangrene, sepsis, pneumonia, abdominal and urinary infections,infections due to susceptible bacteria resistant to other antibiotics, and (except for ertapenem) Pseudomonas infections

Seizures (especially with imipenem)

Cephalosporins, 1st generation

Mainly skin and soft-tissue infections
Gastrointestinal upset and diarrhea
Allergic reactions

Cephalosporins, 2nd generation

Some respiratory and, for cefoxitin, abdominal infections
Gastrointestinal upset and diarrhea
Allergic reactions

Cephalosporins, 3rd generation

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
Allergic reactions

Cephalosporins, 4th generation

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
Allergic reactions

Cephalosporins, 5th generation

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)



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, sometimes fatal liver damage


Complicated abdominal infections and complicated skin infections due to susceptible bacteria, such as Escherichia coli, Staphylococcus aureus (including those resistant to methicillin), 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



Streptococcal infections, syphilis, respiratory infections, mycoplasmal infections, and Lyme disease
Nausea, vomiting, and diarrhea (especially at higher doses)
Abnormal heart rhythms


Infections caused by gram-negative bacteria
Allergic reactions
Can be used in patients allergic to antibiotics such as penicillins, cephalosporins, and carbapenems



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)
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)


Urinary tract infections (except sulfasalazine, sulfacetamide, and mafenide)
For mafenide 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



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

Typhoid, other salmonellal infections, and meningitis
Severe decrease in white blood cell count (rare)
Streptococcal and staphylococcal infections, respiratory infections, and lung abscess
Antibiotic-associated diarrhea and inflammation of the colon (colitis)
Complicated skin infections, bloodstream infections, and certain heart valve infections (endocarditis) due to susceptible bacteria, including methicillin-resistant Staphylococcus aureus (MRSA)
Not used when infection involves the lungs

Gastrointestinal upset
Muscle pain and weakness

Vision disturbances
Bladder infections

Nausea and vomiting
Serious infections caused by gram-positive bacteria that are resistant to many other antibiotics
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)

Vaginitis caused by Trichomonas or Gardnerella species and pelvic and abdominal infections
Headache (especially if the drug is taken with alcohol)
Metallic taste
Numbness and tingling in the hands and feet (peripheral neuropathy)
Dark urine
Urinary tract infections
Nausea and vomiting
Liver dysfunction
Gout (occasionally)
Serious infections caused by gram-positive bacteria that are resistant to other antibiotics
Aching muscles and joints
Tuberculosis and leprosy
Liver dysfunction
Red-orange saliva, sweat, tears, and urine
Mild to moderate community-acquired pneumonia (Community-acquired pneumonia refers to pneumonia acquired outside of hospitals or extended-care facilities)

Visual disturbances
Liver damage (possibly fatal)
Worsening of symptoms in people with myasthenia gravis (possibly fatal)
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.

Gonorrhea spreads easily and can lead to infertility in both men and women, if untreated. Antibiotics stop the infection
Symptoms: Common symptoms are burning during urination and discharge, but often there are no early symptoms. Later, the infection may cause skin rashes or spread to the joints and blood.

In Men: Discharge from the penis, swollen testicles.

In Women: Vaginal discharge, pelvic pain, spotting. Symptoms may be mild and are easily confused with a urinary tract or vaginal infection.

Most people don't notice the early symptoms of syphilis. Without treatment, it can lead to paralysis, blindness, and death. Syphilis can be cured with antibiotics.

Signs and Symptoms: The first sign is usually a firm, round, painless sore on the genitals or anus. The disease spreads through direct contact with this sore. Later there may be a rash on the soles, palms, or other parts of the body (seen here), as well as swollen glands, fever, hair loss, or fatigue. In the late stage, symptoms come from damage to organs such as the heart, brain, liver, nerves, and eyes.

Chlamydia is a common STD that can lead to infertility if left untreated. It clears up quickly with antibiotics. But it often goes unnoticed because symptoms are vague or absent. Chlamydia can also infect the rectum and throat.

Symptoms in Men: Burning and itching at the tip of the penis, discharge, painful urination.

Symptoms in Women: Vaginal itching, discharge that may have an odor, pain during sex, painful urination.

Trichomoniasis is caused by a parasite that spreads during sexual contact. It can be cured with prescription drugs.

Signs and Symptoms in Men: Most men have no obvious symptoms. Some develop a mild discharge or slight burning during urination.

Signs and Symptoms in Women: Women may develop a yellow-green discharge with a strong odor, vaginal itching, or pain during sex or urination. Symptoms usually begin 5 to 28 days after acquiring the parasite.

Not an STD itself, pelvic inflammatory disease (PID) is a serious complication of untreated STDs, especially chlamydia and gonorrhea. It happens when bacteria spread to infect the uterus and other female reproductive organs. Prompt treatment is essential to prevent damage to a woman's fertility.

Signs and Symptoms: Lower abdominal pain, fever, unusual discharge, painful intercourse, painful urination, and spotting. There are often no warning signs.

Lyme disease is a bacterial illness caused by a bacterium called a "spirochete," which may be transmitted to humans by the bite of infected ticks (Ixodes scapularis and Ixodes pacificus). The actual name of the bacterium in the United States is Borrelia burgdorferi. In Europe, another bacterium, Borrelia afzelii, also causes Lyme disease.

Staphylococcus is a group of bacteria that can cause a multitude of diseases as a result of infection of various tissues of the body. Staphylococcus is more familiarly known as Staph (pronounced "staff"). Staph-related illness can range from mild and requiring no treatment to severe and potentially fatal. Over 30 different types of Staphylococci can infect humans, but most infections are caused by Staphylococcus aureus. Staphylococci can be found normally in the nose and on the skin (and less commonly in other body locations) of 25%-30% of healthy adults. In the majority of cases, the bacteria do not cause disease. However, damage to the skin or other injury may allow the bacteria to overcome the natural protective mechanisms of the body, leading to infection.

This tiny cluster of bacteria is methicillin-resistant Staphylococcus aureus (MRSA), seen under a microscope. This strain of the common "staph" bacteria causes infections in different parts of the body - including the skin, lungs, and other areas. MRSA is sometimes called a "superbug" because it is resistant to many antibiotics. Though most MRSA infections aren't serious, some can be life-threatening.

MRSA Skin Infection: Symptoms

MRSA infections can look exactly like ordinary staph infections of the skin: a small red bump, pimple, or boil. The area may be red, painful, swollen, or warm to the touch. Pus or other fluids may drain from the sore. Most MRSA skin infections are mild, but they can change, becoming deeper and more serious.

MRSA, Spider Bite or Something Else?

Bug bites, rashes, and other skin conditions can be confused with MRSA because the symptoms may be similar: red, swollen, warm, or tender. ER doctors routinely ask patients who arrive with a painful spider bite whether they actually saw the spider, because these "bites" so often turn out to be MRSA instead. When a skin infection spreads or does not improve after 2-3 days on usual antibiotics, it may be MRSA.

MRSA Skin Infection: Cellulitis

MRSA can lead to cellulitis, an infection of the deeper layers of skin and the tissues beneath. On the surface, the skin looks pink or red, like a sunburn, and may be warm, tender, and swollen. Cellulitis may spread quickly over a few hours.

MRSA Skin Infection: Abscess

MRSA can sometimes cause a deeper infection called an abscess, which is a collection of pus that can be underneath the skin. A minor skin infection that goes without proper, timely treatment, can develop into an abscess. This type of infection may require surgical drainage and antibiotics to heal.

MRSA: How Do People Catch It?

MRSA can spread through physical contact with an infected person or something you've touched. Conditions that help to spread MRSA include: close skin-to-skin contact; cuts or scrapes in the skin; sharing personal hygiene articles such as razors and towels; and contact with contaminated items including door handles and athletic equipment. One in 100 people carry the bacteria on their bodies, but don't get sick.

Who Gets MRSA?

People who've recently had surgery or a hospital stay have an increased risk of developing MRSA. It's also seen in older people, those living in nursing homes, and people with weakened immune systems. A chronic medical condition like diabetes, cancer, or HIV increases your chances of getting this stubborn infection.