Prescription Drugs Information


Antibacterial Drugs


What Are Antibiotics?

Antibiotics are medications used to treat infectious diseases caused by bacteria. Penicillin was the first antibiotic discovered (in 1927). Since that time, more than 150 types of antibiotics have been developed. These drugs have dramatically lowered rates of death and illness associated with infectious disease.

Bacteria are tiny, single-cell living organisms. They can be found everywhere in the environment, including both on and within the human body. Most bacteria are harmless, and some are beneficial. However, certain bacteria cause infection when they are introduced into the human body. Once inside, bacteria reproduce rapidly, disrupting normal function and causing illness.

Antibiotics work to eliminate these microorganisms by halting their ability to grow and reproduce. Each type of antibiotic is effective against certain types of bacteria. About 90 percent of the antibiotics used today are created by chemically isolating them from bacteria, although a few are completely manufactured. “Broad spectrum” agents are antibiotics that harm or kill a wide variety of infectious bacteria.

Antibiotics can harm bacteria in several ways. Most antibiotics fall into one of the following categories:

  • Cell membrane inhibitors. These antibiotics directly kill bacteria cells by causing the outer membrane of the cell to break down. Most medications of this kind are used as topical antibiotics, such as skin ointments or creams. These types of antibiotics are not effective when administered systemically (provided to the entire body through the bloodstream, such as when taken in pill form).
  • Cell wall synthesis inhibitors. These antibiotics will not harm existing bacteria cells, but they prevent new bacteria cells from forming. Infections grow and spread because bacteria cells multiply rapidly, doubling their presence in the body once every 20 minutes. When bacteria divide in order to multiply, they create a wall or container for the new cell. Antibiotics considered cell wall synthesis inhibitors prevent bacteria from forming this cell wall, thus preventing bacteria from multiplying.
  • Protein synthesis inhibitors. These antibiotics prevent bacteria from converting proteins to energy, effectively starving bacteria to death.
  • Nucleic acid synthesis inhibitors. These antibiotics prevent bacteria cells from growing by interrupting communication between bacteria and its deoxyribonucleic acid (DNA) – the genetic material of the bacteria that tells it how to make proteins to survive and reproduce.
  • Competitive inhibitors. These antibiotics are mostly synthetic (manufactured) and are similar to the material in bacteria that regulate growth. Once this medication reaches bacteria, it replaces the bacteria's own growth-regulating material, preventing an infection from spreading.

Antibiotics are typically administered in oral form, although they also may be applied as topicals (applied directly to the skin) or injections, including intravenous injections (which are injected directly into the bloodstream). Antibiotics are taken until the infecting organism is completely eliminated from the body, which often does not occur until several days after symptoms cease. For this reason, antibiotics are rarely prescribed for periods of fewer than five days.

Different antibiotic drugs or combinations of drugs may be used to treat various conditions. Generally, treatments may be classified according to their effectiveness in the following manner:

  • First-line treatments: The first medication prescribed for treatment of a given diagnosis. First-line drugs are the most frequently used medications due to their low risk of toxicity (overdose), relatively low cost and broad availability.
  • Second-line treatments: The second medication provided if the patients have either relapsed following first–line treatment or were unresponsive to the initial drug used. Second-line treatments have a comparatively higher risk of side effects than first-line treatments.
  • Third-line treatments: These medications are provided when resistance develops to a second-line drug. Third-line treatments carry a greater risk of toxicity and other side effects than first- or second-line treatments. Consequently, they are only given when the potential benefits of a third-line medication are believed to outweigh its risks.

After a physician identifies the type of bacterium responsible for a person’s illness, a specific type of antibiotic known to be effective against that particular bacterium will be prescribed. In some cases, infection is the result of several different types of bacteria or a bacterium that does not have an established track record of being treated effectively by a certain type of antibiotic. In such instances, a physician may order laboratory tests to examine the effect of various antibiotics on the bacterium. When a promising drug is identified, it will be prescribed to the patient.

The effectiveness of an antibiotic depends on many factors, including how well the drug is absorbed into the bloodstream, how much of the drug reaches the site of infection in the body and how quickly the body eliminates the drug from the system.


Types and differences of antibiotics

There are more than 150 types of antibiotics available to treat a variety of infectious diseases caused by bacteria. Some of the more commonly prescribed antibiotics include:

Drug ClassGeneric NameBrand Name(s)



Amoxil, Polymox






Merrem IV



Cefizox, Rocephin



Cidomycin, Garamycin
Mycifradin, Myciguent



Dynacin, Minocin
Robitet, Panmycin












Floxin, Ocuflox


Conditions treated with antibiotics

Antibiotics are usually prescribed to treat bacterial infections. Such infections can cause many different types of illnesses, including:

  • Pneumonia
  • Strep throat
  • Urinary tract infections
  • Wound and skin infections (caused by Staph bacteria)
  • Certain sexually transmitted diseases (e.g., chlamydia, gonorrhea, syphilis)
  • Certain types of ear infections

In some cases, antibiotics are prescribed as a prophylactic measure to prevent infection. For example, people with artificial or abnormal heart valves often are required to take antibiotics before dental procedures. Antibiotics may also be used as a prophylactic in people with weakened immune systems. This may include patients with leukemia, AIDS and those undergoing chemotherapy treatment for cancer.

Antibiotics only treat infections caused by bacteria. They are not effective against any other type of infection, such as viral or fungal infections. In some cases, a physician may not know whether a virusvirus or bacteria is causing the infection, and may only prescribe antibiotics if the infection persists.

Side effects

Potential side effects of antibiotics

Antibiotics typically do not cause serious side effects. Some people may experience symptoms of minor discomfort, such as upset stomach. A person’s rate of digestion may be affected by antibiotics, causing food to leave the stomach and enter the intestines too early and increasing intestinal contractions, both of which can contribute to diarrhea. Antibiotic use can also increase a person’s photosensitivity (likelihood of sunburn when exposed to sunlight).

Vaginal yeast infections (candidiasis) are a common side effect of antibiotic use in women. By reducing bacteria levels, antibiotics can cause an overgrowth of other organisms in the body, such as yeast.

Yeast infections are treatable with both prescription and over-the-counter medications. These types of infections may also be avoided by the daily consumption of “live culture” yogurt (available at most grocery stores) while undergoing antibiotic treatment.

Some side effects associated with antibiotic use may be severe. Patients who take antibiotics may experience antibiotic-associated diarrhea (AAD). This occurs when antibiotics disrupt the natural bacterial balance in the body by killing too many good “good” bacteria, allowing “bad” bacteria to flourish in the intestinal tract. As the number of bad bacteria increase, the patient may experience frequent, watery bowel movements. Usually, a mild case of AAD begins about five to 10 days after starting antibiotic therapy. However, in some cases, AAD may be more severe. Such episodes can lead to inflammation of the large intestine (antibiotic-associated colitis) that causes abdominal pain, bloody diarrhea and fever.

A more serious version of this illness (pseudomembranous colitis) is potentially deadly. Concentrated supplements of beneficial bacteria (e.g., lactobacillus acidophilus) or consuming yogurt can sometimes help prevent or relieve symptoms associated with AAD.

Adverse reactions to antibiotics may be more serious in patients with weakened immune systems (e.g., due to HIV & AIDS). Some patients may also experience an allergic reaction, including a skin rash with or without itching. Severe allergic reactions include swelling, hives, shortness of breath and collapse (anaphylactic shock).

Patients who experience serious side effects associated with antibiotic use should seek medical attention. These side effects include:

  • Hives
  • Skin rash
  • Fever
  • Nausea
  • Dark or discolored tongue
  • Dizziness or lightheadedness
  • Abnormally fast heartbeat (tachycardia)
  • Unusual fatigue or weakness
  • Headache
  • Ringing in ears or deafness
  • Bloating
  • Unusual thirst
  • Loss of appetite
  • Weight loss
  • Unusual bleeding or bruising
  • Confusion
  • Back or joint pain or stiffness
  • Jaundice (yellow eyes and/or skin)
  • Itchiness of armpits, groin or rectum
  • Muscle twitches or spasms
  • Convulsions or seizures

Other possible but relatively rare complications include kidney failure and liver abnormalities.


Antibiotic resistance

Improper or excessive use of antibiotics can result in a condition known as antibiotic resistance. Antibiotics are developed to kill or neutralize specific bacteria. In some cases, bacteria and other microbes may adapt to this threat.

They may develop the ability to rapidly pump the antibiotic from the system or alter the site of antibiotic attacks, steering antibiotics away. Some microbes may undergo a mutation in their genetic material that allows them to become resistant to antibiotics. This mutation increases a person’s risk of being infected by bacteria that are difficult to treat.

Antibiotic resistance is a worldwide healthcare concern. In the last decade or so, many types of bacteria have become stronger and more resistant to antibiotics. New strains of antibiotic-resistant bacteria are continually emerging. In many cases, these strains can be treated with stronger antibiotics. However, eventually the bacteria begin to adapt to even these more powerful drugs.

Antibiotic-resistant germs can quickly become a threat to the health of family members, classmates and others in the community. This is because it is the microbe – and not the individual person’s body – that becomes resistant to the antibiotic. As an infection passes from person to person, the potential for a significant health crisis grows.

Patients who use antibiotics excessively or inappropriately are at risk of allowing the bacteria and other microbes in their bodies to become resistant to the medication. For this reason, patients are urged to strictly follow their physician’s recommendations while taking antibiotics.

Tactics to help slow the creation of antibiotic-resistant germs include the following:

  • Do not take antibiotics for viral infections. Illnesses such as the common cold, influenza, most sore throats, and most coughs and bronchitis are the result of viral infections rather than bacterial infections. Antibiotics cannot kill viruses, so taking antibiotics to treat such illnesses is not helpful and creates the potential for more antibiotic-resistant strains to emerge.
  • Take antibiotics exactly as prescribed. Do not skip doses of the medication. In addition, take all of the antibiotic medication prescribed, even if symptoms stop. Blood levels of the antibiotic must stay within a high enough range to kill bacteria. People also should not take antibiotics prescribed for someone else. Doing so may delay appropriate treatment and can allow bacteria to multiply.
  • Do not save antibiotics for future illness. Over time, the quality of medication contained in an antibiotic degrades and may be unsafe for consumption or ineffective against bacteria.
  • Avoid certain “antibacterial” soaps and cleansers. Choose products with bleach, alcohol, ammonia or hydrogen peroxide. Products with these chemicals kill bacteria without promoting resistance. At present, it is not known whether or not the use of antibacterial soaps increases antibiotic resistance.
  • Keep vaccines up-to-date. Many bacterial infections can be prevented through immunization. Patients can discuss their options with a physician.

Drug or other interactions with antibiotics

Patients should consult their physician before taking any additional prescriptions, over-the-counter medications, nutritional supplements or herbal medications while taking antibiotics. Of particular concern to individuals taking antibiotics are:

  • Other antibiotics. Physicians may prescribe several different types of antibiotics to be taken simultaneously to treat certain types of infections, but the use of multiple antibiotics can also increase the risk of side effects.
  • Anticoagulants. Medications that prevent the formation of blood clots. Certain types of antibiotics may increase the effect of anticoagulants.
  • Antacids. Medications that balance gas and acids in the stomach. The use of antacids with certain antibiotics (e.g., fluoroquinolones, tetracyclines) may decrease the effectiveness of both medications.
  • Insulin. The antibiotic tetracycline has been shown to interfere with insulin production in the body and increase a person’s insulin resistance.
  • Nonsteroidal anti-inflammatory drugs (NSAIDs). Medications that reduce pain and inflammation by inhibiting the production of certain chemicals in the body. Certain antibiotics may increase the incidence or severity of side effects due to NSAIDs.
  • Antiviral medications. Certain antibiotics may decrease the effectiveness of these virus-fighting medications.
  • Diarrhea medications. These may increase the effects of certain types of antibiotics.
  • Calcium supplements. These may decrease the effectiveness of certain types of antibiotics.
  • Oral contraceptives. Medications that control a woman’s menstrual cycle and prevent pregnancy. Antibiotics can lessen the effectiveness of birth control pills, and women may require a back-up birth control method.
  • Bronchodilators. Medications that widen airway passages in the lungs and are often used in the treatment of asthma. Certain types of antibiotics may increase the concentration levels of some bronchodilators, although the two medications are routinely used together.
  • Gout medications. Gout is a painful joint inflammation. Gout medications may increase the effects of certain types of antibiotics.
  • Alcohol. Certain antibiotics may increase the risk of liver damage from alcohol abuse.
  • Caffeine. Certain antibiotics may increase the risk of toxicity (or overdose) from caffeine.
How to use

Pregnancy use issues with antibiotics

The U.S. Food and Drug Administration (FDA) has classified most antibiotics as belonging in either category B or category C. Category B indicates that either animal studies have shown no risk to an animal fetus, but there have been no human studies, or that animal studies have revealed a risk to an animal fetus but human studies have revealed no risk. Category C indicates that animal studies have shown a risk to animal fetuses, but the drugs have not been adequately studied in humans.

The use of antibiotics during pregnancy or while breastfeeding depends on the nature of the infection and the potential benefits and risks to both the mother and baby. In many cases, the benefit of treating an infection may outweigh a slight or theoretical risk associated with the medication.

Certain classes of antibiotics generally have been considered safe throughout pregnancy, including the penicillins and cephalosporins. Others should be avoided during certain trimesters because they may interfere with embryonic or fetal development. Tetracyclines are usually avoided during the first trimester because they may affect developing bones. In the second trimester, aminoglycosides may be toxic to auditory development in the fetus. Still other antibiotics should be avoided throughout pregnancy, such as quinolones.

During the third trimester, a pregnant woman may be tested for group B strep infection. This infection may cause no problems but may be passed to the infant during delivery. Women who test positive for the infection are given antibiotics during labor to prevent transmission to the baby.

Similar benefits and risks apply to antibiotic use while breastfeeding. Some antibiotics pass into breast milk and others do not. During pregnancy, most of the medications are processed by the mother's liver and kidneys. After birth, the infant's liver and kidneys must filter the medications that pass through breast milk. The filtering capacity of the infant's organs are much lower than those of the mother. A woman may be advised not to breastfeed while taking certain antibiotics.

Pregnant and breastfeeding women should consult their physicians about any antibiotic use.

Child use issues with antibiotics

Most antibiotics are safe for use in children. Certain antibiotics are not, such as tetracycline, which has been shown to delay bone growth and discolor developing teeth. Thus, tetracycline is not recommended for use in children under age 9. Parents should consult their child’s pediatrician about the types of antibiotics that may be appropriate for their child.

Frequent or inappropriate use of antibiotics in both children and adults has made many strains of bacteria resistant to antibiotic treatment. Because children have weaker immune systems than healthy adults, the emergence of antibiotic resistance is an especially serious children’s health issue. A physician should be notified immediately if a child’s condition does not begin to improve within one to two days following treatment with antibiotics because this may indicate the presence of antibiotic-resistant bacteria.

Elderly use issues with antibiotics

In most instances, antibiotics may be administered to elderly individuals in much the same way as younger adults. However, older adults may have specific issues related to antibiotics and are encouraged to consult a physician prior to beginning antibiotic treatment. Reduced doses and longer dosing intervals may be necessary for older people. In addition, older adults are more likely to spend time in hospitals and nursing homes, which may increase their risk for side effects and complications associated with antibiotic use, such as antibiotic-associated diarrhea or pseudomembranous colitis.

Symptoms of antibiotic overdose

Symptoms of antibiotic overdose can be similar to the medication side effects, but are usually more severe. Patients exhibiting any of these symptoms should contact their physician immediately:

  • Nausea
  • Vomiting
  • Inability to coordinate muscle movement
  • Seizures

Questions for your doctor regarding antibiotics

Patients may wish to ask their doctor the following antibiotic-related questions:
  1. Are antibiotics required to treat my medical condition? Should I try something else before taking antibiotics?
  2. Which antibiotics are likely to help my condition?
  3. What are the side effects associated with the antibiotics you are recommending for me? Are there alternative types of medications you recommend?
  4. Which, if any, side effects should I immediately report to you? Which are likely to resolve with time?
  5. What is the risk of my developing diarrhea or pseudomembranous colitis with the antibiotics you are recommending? Is this of particular concern for me?
  6. If these side effects or complications occur, how should they be treated? Are there over-the-counter medications you recommend?
  7. Are there any over-the-counter medications that I should avoid taking while using the antibiotic you are prescribing?
  8. Are there any dietary changes I can make to reduce the potential side effects of these antibiotics?
  9. Are there any lifestyle changes that may help?
  10. Are antibiotics safe to use if I am pregnant or breastfeeding? What types of antibiotics would you recommend in these cases?

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