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What are Antibiotics?

Last updated on 3rd May 2023

Bacteria are tiny microorganisms, many of which can be helpful to the human body, with less than 1% of all known bacteria actually causing diseases in humans. However, when disease-causing bacteria enter the body, it can lead to an infection. When this happens, it is sometimes necessary to treat this infection with medicine known as antibiotics.

Penicillin, one of the most common types of antibiotics, was first discovered in 1928 and antibiotics started being widely used in the 1940s and 1950s. Since then, they have saved the lives of millions of people who would have otherwise died from infection.

Unfortunately, due in part to overuse, antibiotic resistance has occurred, meaning that some strains of bacteria can no longer be successfully treated with antibiotics in the way they once were.

To help reduce instances of antibiotic resistance it is important that antibiotics are used sensibly and for the correct ailments.

What are antibiotics?

Antibiotics are a type of medicine that is routinely used to treat or prevent some infections that are caused by bacteria.

Infections can be caused by bacteria, viruses and fungi and these infections can result in disease. The signs and symptoms of these diseases can range in severity from mild to moderate to very serious.

Only bacterial infections can be treated with antibiotics, meaning that if your infection is viral or fungal in nature you will need an alternative course of treatment. For the majority of people, mild bacterial infections will not require antibiotics.

Taking antibiotics to help treat infection

When are antibiotics needed?

Sometimes, bacterial infections can clear up by themselves, especially if the infection is only a moderate one. This is why a prescription for antibiotics is no longer immediately given out for common problems such as a chest infection or childhood ear infection.

Certain bacterial infections are more severe than others and they can be especially dangerous to those who are immunocompromised, very young or elderly. People in these groups might be more vulnerable to the effects of a bacterial infection and will require antibiotics to help them to recover.

For the general population, it is usually only necessary to take antibiotics when:

  • An infection is not clearing up without them or is unlikely to clear up on its own.
  • There is a risk of more serious complications if the infection is not treated.
  • Other people are at risk of becoming infected.

People who are at a very high risk of developing infections are sometimes given antibiotics as a precaution to reduce the chances of an infection developing. This is referred to as antibiotic prophylaxis.

Some common bacterial infections that usually require a course of antibiotics include:

  • Urinary tract infections (UTIs).
  • Sexually transmitted infections (STIs) such as chlamydia.
  • Pneumonia – Your doctor will need to perform tests to find out if your pneumonia is caused by a virus or bacteria so that you can get the right treatment.
  • Tooth infections/dental abscesses.

Antibiotics are also used to treat infections that occur in open wounds, those related to childbirth or breastfeeding (such as mastitis) and infections that occur post-surgery due to unsanitary equipment or conditions. They are also necessary in parts of the world where people still suffer from diseases such as tuberculosis (TB) where vaccinations are not widely available.

It is important to remember that antibiotics are not effective against other illnesses such as viruses. This means, for example, that taking antibiotics if you have the common cold or flu would not make you feel better, no matter how strong they are or how long you take them for.

Some medical problems such as meningitis or pneumonia can be viral or bacterial. This means it is important that your doctor makes the correct diagnosis and finds the underlying cause so you can get the correct treatment.

What are the different types of antibiotics?

In general, the hundreds of different types of antibiotics can be classified into six separate groups:

  • Aminoglycosides (for example tobramycin, neomycin) – This class of antibiotics are usually reserved for serious infections and are given intravenously in hospital as they are not absorbed well when given orally. They can have serious side effects including kidney failure and hearing loss.
  • Cephalosporins (for example cefalexin, cefadroxil) – This group of antibiotics are given orally for less serious infections such as skin infections, but when administered intravenously can be effective in treating serious infections such as meningitis and sepsis.
  • Fluoroquinolones (for example ciprofloxacin, moxifloxacin) – These are no longer used widely for a range of infections due to side effects including tendon problems, hypoglycaemia and nerve pain. These antibiotics are especially effective against respiratory and urinary tract infections and may also be useful against less common infections including the plague.
  • Macrolides (for example clarithromycin, fidaxomicin) – These are effective against a wide range of infections, and are often used as an alternative in patients who are allergic to penicillin or in cases of drug resistance where penicillin has not been effective.
  • Penicillins (for example penicillin, amoxicillin) – These are very common antibiotics used to treat a range of infections from pneumonia to UTIs.
  • Tetracyclines (for example doxycycline, tetracycline) – These are applied topically, and are useful in treating or preventing skin infections. It is also widely prescribed as a course of tablets to be taken orally in patients with sexually transmitted diseases and can also be prescribed to prevent malaria.

Your doctor will need to prescribe you the correct type and strength of antibiotic based on your condition, symptoms and medical history.

Antibiotics being given intravenously

How are antibiotics taken?

If you are prescribed antibiotics, you will receive an information leaflet in the box along with your medication. This will contain important information about the antibiotics.

This should include details about their:

  • Active ingredients/other ingredients.
  • Possible side effects.
  • Dosage and instructions.

There should also be a printed label on the box that outlines how and when you should take the medicine and for how long. They will usually be prescribed in a pill or capsule form that is swallowed whole with water.

As with any medicine, it is important that you take the antibiotics as directed and that you complete the course. Even if you begin to feel better before you have finished all of the medication:

  • Take the correct dose as directed in the instructions.
  • Space doses out evenly throughout the day or as directed.
  • If you forget to take your antibiotic, take it as soon as you remember.
  • Complete the full course.
  • Speak to a medical professional if you have any concerns or questions.

Although usually prescribed as a tablet or capsule, antibiotics can also be given in different forms, such as:

  • Liquid medicine that is swallowed (particularly if being used by infants/young children).
  • Lotions, creams, sprays or drops that are applied topically or directly to the affected area (usually for skin or eye infections).
  • Injections that are given intravenously either through a drip or as an injection directly into the bloodstream or muscle (this method is used to treat more serious infections).

Occasionally, a bacterial infection does not clear up after the initial course of treatment. In this case it may be necessary to:

  • Repeat the course.
  • Take stronger or different antibiotics.
  • Explore different treatment options.

If you find your symptoms do not improve once you have finished your course of antibiotics you should speak to your doctor as soon as possible. You should never ignore your symptoms or start any new treatment without consulting a medical professional.

How do antibiotics work?

When certain bacteria, viruses or other microbes enter into the body and begin to multiply, they can cause an infection. As the cells in your body get damaged as a result of the infection, you will start to show the signs and symptoms of illness.

Antibiotics are designed to kill bacteria or to stop them from growing. Some types of antibiotics will attack the bacterium’s cell wall, damaging and eventually killing off the cell. Others are designed to inhibit the ability of the bacteria to grow or multiply.

Each bacterial cell is surrounded by a cell wall. To multiply, the individual bacteria cells split into two, then these two will divide into four. This is called binary fission. Bacteria can reproduce in vast numbers very quickly. An antibiotic can disrupt this process by attaching itself to the cell wall so that the cell can no longer divide and is eventually destroyed.

Are there side effects with antibiotics?

You should always refer to the patient information leaflet that came with your medication and only use prescription medication as prescribed.

Antibiotics can cause side effects; common ones include:

  • Nausea and sickness.
  • An upset stomach, cramping or bloating.
  • Diarrhoea.

Occasionally people may suffer serious side effects or an allergic reaction to their antibiotics including rashes, breathing problems or internal bleeding. When used as directed, serious side effects from antibiotics are rare; however, if you are unsure of anything you should contact your GP or call the NHS 111 helpline for advice. In an emergency always dial 999.

Antibiotics do not usually cause drowsiness but certain antibiotics can alter the efficacy of other medication and the contraceptive pill. To avoid becoming pregnant, you may need to use another form of birth control whilst taking antibiotics.

Antibiotics can also react with other agents. Some antibiotics, for example, do not mix well with alcohol. Sometimes you will be directed to take your antibiotics on an empty stomach, whilst others must be taken with or after food. Herbal medicine, such as St John’s Wort, can also interact negatively with antibiotics and other prescribed medication. This is why it is so vital to read all of the information that comes with your medicine and only use it as directed.

Remember antibiotics must be taken as directed and you should never:

  • Take antibiotics if you know you are allergic to any of the ingredients.
  • Share antibiotics with other people.
  • Take prescription medicine that you have not been prescribed by a doctor.
  • Buy antibiotics online from unregistered or unknown vendors.
  • Double up doses when you forget to take your antibiotics.
  • Stop taking your antibiotics before you have finished the course.

Antibiotics are often given in courses of 3, 7 or 14 days, depending on the type and severity of the infection and the class of antibiotic that has been prescribed. You will usually begin to feel better after taking the medication, as directed, for several days.

Prescription being given to patient

Can you become resistant to antibiotics?

Antibiotics used to be widely prescribed; however, this is no longer the case. This is because antibiotic resistance is a serious problem. It is also due to a better understanding of how antibiotics work and when they are most useful.

  • Viruses, rather than bacteria, cause multiple infections and antibiotics are not at all effective against viruses.
  • Antibiotics cause side effects and are not always able to expedite the body’s natural healing process.
  • If antibiotics are over-prescribed to treat minor bacterial infections, a person can build up resistance. This means they are more likely to find that antibiotics are not effective if they develop a more serious infection in the future.

Global health organisations, including the NHS, are working to reduce reliance on antibiotics, especially for minor infections that will likely get better by themselves. This is because when people become resistant to antibiotics it can cause serious and even fatal consequences.

When bacteria become resistant to antibiotics it means that they can continue to grow and multiply even when they are exposed to the medicine that is designed to kill them.

Antibiotic resistance has led to ‘superbugs’ appearing in hospitals; these superbugs have developed resistance to a range of different antibiotics, making them very hard to control and treat.

These include:

  • MRSA (methicillin-resistant Staphylococcus aureus).
  • Clostridium difficile (C. diff).
  • Drug-resistant tuberculosis (DR-TB).

When infections become resistant to one or many types of antibiotics this limits the number of treatment options available, leading to higher mortality rates in patients. Antibiotic-resistant infections can also be challenging and costly for doctors to treat.

Scientific researchers are currently working on finding new drugs that will be effective against antibiotic-resistant superbugs.

Antibiotics are usually prescribed for short-term use to clear up a bacterial infection. They are not effective against infections that are caused by anything other than bacteria. Over the last 80 years since they have been widely available, antibiotics have undoubtedly saved countless lives. Unfortunately, their overuse and misuse has led to antibiotic resistance, meaning that despite their lifesaving capabilities, antibiotics should be used with caution.

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About the author

Vicky Miller

Vicky Miller

Vicky has a BA Hons Degree in Professional Writing. She has spent several years creating B2B content and writing informative articles and online guides for clients within the fields of sustainability, corporate social responsibility, recruitment, education and training. Outside of work she enjoys yoga, world cinema and listening to fiction podcasts.

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