Antibiotics in Modern Medicine

Antibiotics are a class of medications that kill off or stop the reproduction of bacteria. Thanks to their antimicrobial agents they treat a range of bacterial infections, starting from mild bacterial infections to those more severe, which could result in a life-threatening disease. Before they were discovered people died from common bacterial infections like strep throat, or due to complications after surgeries that now are completely preventable. Despite their wonderful qualities it is important to use them with precaution. Taking antibiotics not as intended might cause unwanted side effects, or even contribute to the global problem of antibiotic resistance. In this article, we will learn all the essentials about antibiotics, how to properly take them to effectively eliminate infection, as well as talk about antibiotic resistance and what can we do to avoid it.
 Zofia Łukaszczyk

Zofia Łukaszczyk

Zofia is a University College London graduate with a bachelor’s degree in biomedical sciences with a focus on neurobiology.

An image of a pill surrounded by bacteria.

What Are Antibiotics?

All of us in our day-to-day lives are exposed to bacteria which might be harmful to our health. Usually, our immune system, responsible for the defence of our body, manages well to get rid of any dangerous pathogens or microorganisms. However, sometimes it might not keep up with the propagation of infection and need extra help. Antibiotic medicine helps with just that. It kills off, stops, or prevents the growth of bad bacteria in the organism, therefore helping us fight off any bacterial infection.

Types of Antibiotics

There are three ways in which we can group different antibiotics, by their:

  • drug administration
  • mode of action: bactericidal vs. bacteriostatic antibiotics
  • spectrum of action: broad vs. narrow-spectrum antibiotics

Administration of Antibiotics

There is a variety of different antibiotics that treat different conditions ranging from skin infections to the innermost organs. As the target of antibiotic therapy changes, the way of taking it does as well. The two main types are oral antibiotics, usually in the form of pills, as well as, topical antibiotics, usually used to treat bacterial skin infections. Antibiotic medicine is also found in the form of injections, e.g. ceftriaxone, which can be injected straight into the blood (intravenous antibiotics), or muscle to treat more severe infections.

Bactericidal vs. Bacteriostatic Antibiotics:

Bactericidal antibiotics work by directly killing the harmful bacteria. Their antimicrobial agents rupture the bacterial cell wall to rupture or interfere with essential cellular functions, such as protein synthesis or other metabolic pathways. For example, the first antibiotic discovered - penicillin inhibits the process of cell wall synthesis, leading to bacterial cell rupture and death.

Bacteriostatic antibiotics, on the other hand, slow down the growth and reproduction of bacteria without directly killing them. This allows the body's immune system to catch up and eliminate the weakened bacteria. This class of antibiotics disrupts protein synthesis, DNA replication, or other cellular processes, causing cell dysfunction. Tetracyclines and macrolides are classic examples of such antibiotics.

Broad vs. Narrow-Spectrum Antibiotics

Bacteria can be divided into two main types, based on the physical and chemical structure of their cell walls. Bacteria with peptidoglycan present are called Gram-positive, and those without Gram-negative. The Gram stain is found by a basic, but very valuable test, which is at default used in clinical and research laboratories.

Broad-spectrum antibiotics target a wide range of bacteria, both Gram-positive and Gram-negative. They are often used when the specific bacteria causing the infection is not known or in common infections when multiple types of bacteria are the cause.

Narrow-spectrum antibiotics are more selective, focusing on a specific group or strain of bacteria. They are advantageous in cases where the infecting bacteria are well-identified and responsive to these antibiotics.

What Are Antibiotics Made From?

In 1928 antibiotics were discovered fully by accident. Sir Alexander Fleming returned to his lab after a holiday when he observed mould growing in his Petri dish with Staphylococcus aureus bacteria. Upon a closer look, he noticed that the mould was preventing bacteria from growing around it. Turns out the mould, Penicillium notatum produced a self-defence substance that killed the bacteria. This led to the development of the first antibiotic, penicillin, which is still widely used to this day. Some antibiotics, similarly to penicillin, are derived from natural products, i.e. microorganisms, while others are designed and produced in a lab by scientists.

Can Antibiotics Treat Viruses? Antibiotics vs. Antivirals

The structure and function of viruses are very different from bacteria. As mentioned before, antibiotics have antibacterial, not antiviral, properties, which means they will not help with common viral infections like flu, common cold, runny noses or stomach flu. For viral infections, antiviral medications have been created. In opposite to antibiotics, antivirals are very specific and can target only one type of virus, which makes them much harder to develop.

Antibiotic resistance

Antimicrobial resistance occurs when microorganisms like bacteria evolve to become immune to antibiotics, or other drugs designed to kill them. This allows them to propagate and form resistant infections, which do not respond to different antibiotics and therefore are much more difficult, if not impossible, to treat. It is one of the top public health threats with even 1.27 mln deaths a year worldwide [1, 2].

Antimicrobial resistance is a natural process that happens through genetic changes in microorganisms. However, overuse or misuse of antibiotics accelerates the development of resistance. There are more than 2.8 mln resistant bacteria infections created each year in the United States alone [2]. This resistance can result in increased risk of disease spread, severe illnesses, disabilities and also death. untreatable infections, posing a serious risk to public health.

How to Prevent Antibiotic Resistance?

To slow down the process of resistant infections the World Health Organization has invented the antimicrobial stewardship program to educate health care professionals to preserve the effectiveness of antibiotic medicine. To do your part in preventing this health crisis please follow these guidelines:

  • take the antibiotic exactly as prescribed, each dosage, for the full duration, even if you start feeling better
  • do not save antibiotics after you're done with your antibiotic therapy, safely dispose of the leftover medicine
  • do not take antibiotics prescribed for someone else
  • consult with your health professional in case of any unusual or severe side effects [3].

What are the side effects of antibiotics?

Taking antibiotics might cause mild side effects, which should pass shortly after you're done with the treatment. The most common side effects include diarrhoea, stomach pain or nausea [4].

Sometimes patients might have an allergy to specific antibiotics, so if you're experiencing any itchy skin rashes, coughing, tightness of the throat, or difficulties breathing you might be having an allergic reaction and you should contact your doctor immediately.

Specific antibiotics might also have other rare side effects. For instance, tetracyclines might increase your skin's sensitivity to light, or fluoroquinolones might cause tingling, numbness or joint pain.

In case of any concerns or questions you have regarding your antibiotic treatment contact your healthcare provider.

How to Prevent Side Effects?

To ensure that antibiotics work as efficiently as they can while minimizing the possibility of side effects it is beneficial these guidelines:

  • take antibiotics as directed: some might be taken only with water, some with food
  • drink 1.5-2l of water per day
  • probiotics:
  • apart from killing the bad bacteria antibiotics also weaken the good bacteria in your gut
  • taking a probiotic will help you prevent bloating or diarrhoea
  • to maximise the beneficial effects take the probiotic a few hours after the antibiotic
  • fermented foods are a great source of gut-healthy bacteria
  • prebiotics:
  • this is the food for the healthy bacteria living in our gut
  • a great natural source of prebiotics is yoghurt, cereals or bread
  • eat a diet rich in fibre
  • helps stimulate the growth of healthy bacteria in the gut [5].

Do Antibiotics Affect Birth Control?

Recent studies show that certain antibiotics, specifically enzyme-inducing antibacterials, decrease the efficiency of birth control pills. The study by Aronson and Ferner from 2021 reports that women taking antibiotics had 7 to 13 times more unplanned pregnancies than women not taking any antibiotics [6]. Many common antibiotics have been shown to interfere with contraception, for instance: rifampin, amoxicillin, ampicillin, griseofulvin, metronidazole, and tetracycline [7, 8].

To prevent pregnancy it is important to be more mindful and use additional birth control as condoms, for the whole duration of the antibiotic treatment and a few days longer. Please remember to contact your care providers in case of any questions or concerns.

Can I Take Antibiotics When Pregnant?

During pregnancy, mothers are advised to be very conscious of their nutrition and anything else they consume, since it filters through the placenta and directly affects the fetus. This also includes antibiotics. Some antibiotic therapies are safe when pregnant, while others might pose serious risks to the pregnancy. Nevertheless, they are still prescribed, with even 1 in 4 women being prescribed antibiotics [9]. Pregnant women's immune systems are often weakened, which makes even common bacterial infections dangerous for the mother, as well as the baby. Some of the most common infections treated with antibiotics in pregnant women are urinary tract infection (UTI), group B streptococcus (strep throat), kidney infections, bacterial vaginosis, or infections of the placenta or the amniotic fluid.

Antibiotics SAFE to take when pregnant:

  • penicillin
  • ampicillin
  • amoxicillin
  • clindamycin
  • erythromycin

Antibiotics UNSAFE during pregnancy, which may lead to hearing loss or stunt bone growth of the fetus:

  • streptomycin
  • kanamycin
  • tetracyclines
  • fluoroquinolones
  • aminoglycosides
  • metronidazole [10].

If you're considering any antibiotic treatments contact your health care provider to discuss potential risks and to ultimately choose the best treatment option most suited for you and your possible health problems. Some other guidelines include: avoiding antibiotic therapy in the first trimester, using the lowest effective dose and of course using antibacterial only if needed and confirmed with a doctor.

Can Antibiotics Affect Blood Work Results?

Antibiotic therapy might have an effect on blood test results, especially those related to liver function and blood cell counts. For instance, certain beta-lactam antibiotics, such as penicillin, cause temporary platelet dysfunction, which might show up in blood work [11].

Therefore it is important to inform your health professional if you are undergoing blood tests while taking antibiotics. This will allow them to analyze results correctly and choose the best treatment.


Antibiotics have revolutionized and shaped modern medicine into what it is today. Since their discovery in the 20th century, they prevented countless health problems and saved millions of lives. To ensure they continue to do so we need to stay educated and remember to use them responsibly to prevent antibiotic resistance. Understanding how to properly use antibiotics is crucial for their effectiveness and for limiting the possibility of severe side effects. Remember to consult your healthcare provider for guidance on any concerns or questions you may have about antibiotics and their impact on your health.

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 Zofia Łukaszczyk

Zofia Łukaszczyk

Zofia is a University College London graduate with a bachelor’s degree in biomedical sciences with a focus on neurobiology. She’s worked on projects ranging from genetics of susceptibility of chronic pain, to studies measuring and analyzing loneliness patterns in older populations. She is most passionate about applying scientific thinking to real-world public health problems, which she will continue as a postgraduate student at the Donders Institute of Radboud Universiteit.