The development of antibiotics was the most significant medical break-through of the 20th century. The overuse of antibiotics has reduced their effectiveness. Learn how antibiotics work, conditions they can treat and those they can’t, common side effects, and how to use antibiotics responsibly.

What are antibiotics? 

Antibiotics are powerful and important medications that are capable of destroying bacteria, which cause certain diseases and infections. They achieve this by blocking bacteria's ability to feed, grow or reproduce, and in doing so the bacteria die.

Surprisingly, about 90% of the antibiotics in use today are made from different types of fungi or bacteria that are naturally capable of destroying or stopping the growth of other microorganisms (in a bid to keep competition at bay). There are also a few antibiotics on the market which are made partially or completely from synthetic materials.

How do antibiotics work?

An antibiotic is a selective poison, in that it can be used to kill bacteria but does not harm the cells in our body. Different antibiotics destroy bacteria is different ways, so each one may be more or less effective on specific types of bacteria.

Antibiotics are classified as narrow-spectrum when they are effective against only a few types of bacteria, and broad-spectrum when they are effective against a wider range of bacteria.

3 different ways antibiotic medications work to destroy bacteria include... 

  • Some block bacteria's ability to turn glucose into energy.
  • Some block bacteria's ability to construct its cell wall.
  • Others interfere with the production of essential proteins need for bacteria's survival. 

The bacteria dies instead of reproducing as a result of any one of these three things occurring.

Why antibiotics are useless against viruses

Both bacteria and viruses are capable of reproducing and causing disease and infections in humans, animals and plants. However, antibiotics are only effective in the treatment of bacterial infections. This is because bacteria and viruses are very different.

Bacteria are tiny single-celled living organisms that can survive independently for long periods of time. Although bacteria can invade our bodies (where they reproduce in the billions) they do not invade the cells of our body. Antibiotics can be used to target bacteria, either killing them or disabling them without destroying the cells of our own body.

A virus is not a cell, but rather a small strand of DNA (or RNA) material that can enter and hide inside the cells of our body. A virus does not feed or reproduce like bacteria do, so unlike bacteria, a virus cannot be destroyed by antibiotics.  Antibiotics have no impact in the treatment of illnesses caused by viruses. 

There are millions of different viruses that affect humans. Most cause minor fleeting illnesses. However, there are some viral infections, such as hepatitis and HIV (AIDS) which cause life long and life threatening conditions.

Although there are over 150 different types of antibiotic medications available today, we only have medications to treat half a dozen or so viruses. These are called anti-viral medications.

How do I know when my child needs antibiotics? 

The answer depends on what is causing your child's illness. The following are some basic guidelines. 

Bacteria cause...

  • Most ear infections
  • Some sinus infections
  • Strep throat
  • Urinary tract infections
  • Skin infections
  • Wound infections
  • Some gastrointestinal infections
  • Illnesses such as pneumonia, meningitis, toxic shock syndrome, leprosy, tuberculosis, scarlet fever and Lyme disease (tick-transmitted). 

Viruses cause...

  • All colds and flu
  • Most coughs or bronchitis
  • Most sore throats
  • Most gastro-intestinal infections
  • Many childhood illnesses such as rubella, chicken pox, measles, mumps etc.
  • Illnesses such as hepatitis, HIV (AIDS), herpes.

A viral infection may temporarily or permanently (in the case of AIDS) weaken your child's (or your) immune system, increasing the risk of a secondary bacterial infection.

Different types of antibiotics 

Today, over 150 different antibiotics are available to cure minor discomforts and well as life-threatening infections. All individual antibiotics are grouped into one of the following families... 

  • cephalosporins
  • fluoroquinolones
  • penicillins
  • erythromycins
  • polypeptides
  • tetracyclines
  • aminoglycosides
  • quinolones
  • streptogramins
  • sulfonamides

Penicillin, erythromycin, amoxicillin and gentamicin are the most widely used antibiotic drugs.


Since penicillin's discovery in 1928 (and its widespread availability in the 1940's) antibiotics have made it possible to cure diseases caused by bacteria which would have previously resulted in the death of millions of people worldwide; for example, pneumonia, tuberculosis and meningitis.

Antibiotics are also responsible for dramatically reducing pain, suffering and disabilities that can develop as a result of severe or prolonged bacterial infections.


Antibiotics are generally safe and helpful in fighting disease but there are certain cases where they can be harmful. Some antibiotics can be harmful if you are pregnant or breastfeeding.

1.  Side effects

Side effects are commonly experienced by babies and young children then taking antibiotics (or in the case of a breastfed baby when the mother is taking antibiotics). Side effects include...

  • nausea (resulting in poor appetite)
  • vomiting
  • diarrhea (affects up to 30% of people)
  • stomach pain
  • lightheadedness
  • headaches

Sometimes certain types of antibiotics, like streptomycin, can damage the nerves involved with balance and hearing. Call your doctor straight away if you or your child experiences any of the following symptoms while taking antibiotics.

  • nausea
  • dizziness
  • 'ringing' sound in ears

Taking the antibiotic erythromycin with Lipitor (a drug used to lower cholesterol) can cause...

  • muscle damage

Some antibiotics such as doxycycline, ciproflaxacin and ofloxacin can cause...

  • light sensitivity

2.  Allergic reactions

Allergic reactions to antibiotics (particular those belong to the penicillin or sulphamide families) are quite common. Some people experiencing an allergic reaction may develop symptoms, such as an itchy rash, hives or breathing difficulties, soon after taking the first dose or within a few days of starting antibiotics.

3.  Antibiotics destroy helpful bacteria

Antibiotics destroy both good and bad bacteria, this includes the friendly gut bacteria (needed for digestion and protection against infection) which keep our intestines healthy. The decline in the number of friendly bacteria allows the yeast (fungus), Candida, which is naturally present in and on our body to overpopulate. Thus a yeast infection is common complication of using antibiotics. 

  • Babies: This overgrowth of yeast may result in intestinal upset, oral thrush or a thrush diaper rash.
  • Women: Antibiotics can lead to vaginal yeast infection. This happens because antibiotics kill the normal bacteria in the vagina, allowing the yeast to grow more rapidly. In the case of a nursing mother, antibiotics may also increase the risk of nipple and/or breast thrush, a painful condition which can cause some women to give up breastfeeding. 

5.  Antibiotics reduce the effectiveness of the contraceptive pill

6.  Antibiotic resistance

Last but far from least important is antibiotic resistance. Antibiotic resistance has become a major health concern facing the world today. It has the potential to impact on the future health of every man, woman and child. 

Bacteria are living organisms; they are always changing in an effort to resist anything that might destroy them. When antibiotics are used incorrectly, bacteria can adapt and become resistent. When resistance develops the antibiotic is no able to kill the bacteria causing the infection.

Antibiotic resistance occurs due to the following reasons...

  • Overuse of antibiotics in humans, animals and agriculture.
  • Unnecessary use of antibiotics (i.e. to treat viral infections).
  • Failure to complete the entire course of antibiotics.
  • Using the wrong type of antibiotics.
  • Inappropriate disposal of unused antibiotics (i.e. down the drain or in the garbage).

Every time an antibiotic is taken, a small number of bacteria may become resistant and survive the treatment. When the survivors reproduce, the entire new crop of bacteria is now resistant, making the antibiotic which was previously effective, useless against these bacteria in the future.

Some strains of Staphylococcus aureus, that may cause boils, pneumonia or bloodstream infections are resistant to almost all antibiotics, making these conditions difficult to treat. Alarmingly, there are a few different kinds of resistant bacteria which are untreatable to any present day antibiotic. The number of different strains of bacteria that become resistant to different types of antibiotics increases each year, and the number of people who become infected with these 'super bugs' worldwide grows every day.

Overuse of antibiotics 

Antibiotics are among the most frequently prescribed medications in modern medicine. Unfortunately, they are also among the most overly prescribed and misused medications. While antibiotics are still the best defense against bacterial infections, more and more they are also being used to 'treat' illnesses that can't be helped by these medications.

How big is the problem of overuse?

HUGE! A study from the Harvard School of Public Health reported that half of the 100 million antibiotic prescriptions written by doctors each year in the USA were prescribed for illness that are not caused by bacteria.

Up to 60% of children with common colds (which are caused by viruses) are treated with antibiotics. About 40% of the time when a child sees a doctor, parents leave with a prescription for antibiotics.

The overuse of antibiotics is not confined to humans but extend to animal and plants as well. Animals like chickens, pigs, turkeys, cattle also receive large doses of antibiotics to improve the rate of growth and the feed efficiency of animals, so that they produce more meat or milk on less feed; and to prevent and treat diseases, just as in humans. Fruits and vegetables are also not spared as antibiotics are sprayed to prevent bacterial infections.

Why does overuse occur?

  • Many doctors report feeling pressured by worried parents or patients to prescribe antibiotics. Doctors feel that parents of babies and children, suffering from a cold or flu, won't be satisfied unless they leave with a prescription.
  • Rather than take the time to explain to parents why an antibiotic is not needed, it is quicker to write a prescription.
  • Sometimes doctors aren't sure whether an infection is caused by a bacteria or a virus, prescribing an antibiotic has been a way doctors make sure "all bases are covered" instead of doing lab test or waiting out the illness.
  • In some countries antibiotics are available over the counter so people self-medicate, often inappropriately. 


1.  Antibiotics will help a child recover from a cold faster

FALSE:  This is one of the common myths that help contribute to overuse of antibiotics. While some parents now realise their child will get over their cold symptoms on their own, many still believe their child will get better faster with antibiotics. Antibiotics will not shorten the length of a viral infection (which causes colds and flu). Taking these drugs just make parents think they are helping their child get better faster. 

2.  A green nasal discharge means a child needs antibiotics

FALSE:  Most colds (which are caused by a viruses) are accompanied by green or yellow runny noses. Because children average 3 to 8 colds each year, treating a green or yellow runny nose with antibiotics would result in many rounds of unnecessary (and therefore harmful) antibiotic medications.

3.  Antibiotics will prevent a secondary infection

FALSE:  Antibiotics won't prevent your child from developing an ear infection or sinus infection when he/she has a cold. In some situations the inappropriate use of antibiotics may weaken your child's natural body defenses making him/her more prone to a secondary infection.

4.  It won't hurt to give antibiotics "just in case"

FALSE:  Every time your child (or yourself) takes an antibiotic that is not necessary, or use antibiotics inappropriately (i.e. stopping before the entire course is completed), it increases your child's chances of some day getting an illness that is resistant to antibiotics.  When given unnecessarily or inappropriately antibiotics may cause an infection to last longer, and instead of getting better your child may get worse. Unnecessary antibiotics put your child at risk of side effects and allergic reactions; it's also a waste of money. 

5.  Its okay to stop taking antibiotics once symptoms improve

FALSE:  To completely clear up infections (and to help prevent antibiotic resistance) antibiotics need to be taken exactly as directed. Do not stop taking the medicines just because symptoms begin to improve.

An antibiotic will normally kill all of the bacteria it targets over the course of a week or 10 days. If your child is feeling better before that time it's because the antibiotic has killed the majority of the bacteria... but not all. The ones that are left may develop resistance to that particular antibiotic. This new strain of resistant bacteria can then multiply, possibly causing a secondary infection. 

Using antibiotics wisely

Antibiotics are used so often these days that we tend to forget that they are strong drugs. Unfortunately the problem of antibiotic resistance means the medical profession now needs to resort to stronger and stronger antibiotics in order to treat common bacterial infections.

The correct use of antibiotics is the best way to ensure that they continue to remain useful in treating infections. There are a number of things you can do to prevent antibiotic-resistant infections in your child and yourself (as well as others), these include...

  • Reduce the risk of illness in the first place by regularly washing your hands thoroughly, and handling food correctly.
  • Never take an antibiotic for viral illnesses such as cold or flu.
  • Take antibiotics exactly as your doctor prescribes them.
  • Take the antibiotic until the course has been completed, even if you are feeling better.
  • Never save antibiotics to treat yourself or others later.
  • Do not discard left over antibiotics down the drain or in the garbage. Return left over antibiotics to your pharmacy for safe disposal.
  • Keep capsules or tablets in a cool dry place.  Store liquid mixtures in the refrigerator.

If side effects occur or if the condition shows no signs of improvement have your child seen by your doctor again.

Written by Rowena Bennett.

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