HomeDiscoverHow It WorksHow long does it take for antibiotics to work?

How long does it take for antibiotics to work?

Bacterial infections are experienced by individuals globally.

In developing countries, infections are considered one of the largest contributors of death. Antibiotics have been around for over a century, aimed at treating bacterial infections.

Due to the prevalence of bacterial infections worldwide, antibiotics are commonly used in healthcare settings for therapeutic treatment.

So, how do antibiotics work? And more specifically, how long does it take for antibiotics to work?

Antibiotics can be used to treat bacterial infections such as urinary tract infections, sinus infections, and strep throat among many others.

They cannot be used to treat viral infections such as the flu or common cold.

In recent times, issues regarding strains of bacteria becoming antibiotic resistant have emerged, likely due to the widespread use of antibiotics globally, challenging the role of antibiotic treatment for bacterial infections.

How do antibiotics work?

Not all antibiotics work the same way in an individual’s body – classes of antimicrobial agents are based on their effect on the bacteria of interest.

There are two general types of antibiotics: bacteriostatic and bactericidal. Bacteriostatic agents will typically inhibit the bacteria’s growth while bactericidal agents will kill the bacterial cells.

This is not always the case, however, as some bacteriostatic agents will kill particular bacterial cells and some bactericidal agents will simply inhibit the cell growth of certain bacteria.

Antibiotics can be further distinguished by their target of a specific cellular component or process in bacterial cells.

For example, antibiotics will typically disrupt the synthesis of DNA, cell walls, or protein in the targeted bacteria. Commonly, bactericidal antibiotics – those which induce cell death – work by targeting the cell wall and bacterial cells’ DNA synthesis.

Bacteriostatic antibiotics will often disrupt the bacterial cells’ growth by inhibiting its protein synthesis.

Choosing the right antibiotic to treat infections is ideally based on the patient’s diagnosis after bacterial culture testing is completed.

Often though, the symptoms which the patient presents will allow the doctor to determine the suspected bacterial source of the infection and prescribe antibiotic treatment before test results are received.

In many cases, especially if the bacterial infection is serious, doctors prescribe broad-spectrum antibiotics, which work by targeting numerous types of bacteria, before a diagnosis based on test results is made.

Once test results reveal the bacterial source of infection, a narrower spectrum antibiotic may be given in replacement of the initial course of antibiotics that may work to better treat the infection.

When determining the right antibiotic to prescribe, a doctor will take into account the patient’s medical history, especially any previous allergic reactions to medications.

The dosage of antibiotics is often selected with the patient’s age, weight, and renal function in mind.

How long does it take for antibiotics to work?

For most cases of mild to moderate bacterial infections requiring treatment, doctors prescribe oral antibiotics which can be taken by an individual at home.

For serious or hospitalized bacterial infections, antibiotics administered intravenously may be required.

The length of the course of antibiotics prescribed by a doctor will depend on the antibiotic drug selected in conjunction with the severity of the bacterial infection and the patient’s response to the antibiotic.

Minor infections may only take days of antibiotic treatment to be treated, whereas for more serious infections, weeks to months of antibiotic treatment may be required.

As such, drug treatment duration will be individualized to each patient’s situation. In recent years, studies have been conducted to provide evidence for an optimal treatment duration, with a focus on limiting antibiotic treatment duration for certain uncomplicated, minor bacterial infections such as urinary tract infections.

It is recommended that in order for the antibiotics to work fully, the entire prescribed course of antibiotics is taken to ensure that the infection is fully treated and to prevent the bacteria strain from becoming resistant to the antibiotic, making the infection difficult to treat.

Side effects of antibiotics

Antibiotic treatment may result in undesirable side effects for patients, similar to most drugs.

Immune system reactions to a prescribed antibiotic are called allergic reactions.

On the other hand, some adverse reactions are due to antibiotic levels in the body that are too high, causing harm rather than simply treating the bacterial infection.

Side effects of antibiotic treatment occur when an individual experiences a reaction not due to an medication allergy or the drug level in the body.

Side effects include, but are not limited to, rash, fever, and diarrhea.

Some groups of people – the elderly, individuals with multiple conditions, hospitalized patients – are more likely to experience a side effect of antibiotic treatment.

Hospitalized patients should be carefully monitored throughout the course of antibiotics for any allergic reactions, harmful drug levels, and presence of side effects.

Non-hospitalized individuals can monitor their own symptoms and call their doctor if they start to feel any side effects while taking antibiotics for further instruction.


Aminov, R. I. (2010). A brief history of the antibiotic era: Lessons learned and challenges for the future. Frontiers in Microbiology1, 134. https://doi.org/10.3389/fmicb.2010.00134

Calhoun, C., Wermuth, H. R., & Hall, G. A. (2020). Antibiotics. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK535443/#_NBK535443_pubdet_

Kapoor, G., Saigal, S., & Elongavan, A. (2017). Action and resistance mechanisms of antibiotics: A guide for clinicians. Journal of Anaesthesiology, Clinical Pharmacology33(3), 300–305. https://doi.org/10.4103/joacp.JOACP_349_15

Leekha, S., Terrell, C. L., & Edson, R. S. (2011). General principles of antimicrobial therapy. Mayo Clinic Proceedings86(2), 156–167. https://doi.org/10.4065/mcp.2010.0639

NHS Inform. (2020). Antibiotics. Retrieved from https://www.nhsinform.scot/tests-and-treatments/medicines-and-medical-aids/types-of-medicine/antibiotics#:~:text=Antibiotics%20are%20used%20to%20treat,most%20coughs%20and%20sore%20throats.

Image by Arek Socha from Pixabay 


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