Antibiotic

An antibiotic is a type of antimicrobial substance that acts specifically against bacteria. Antibiotics are a central component of modern medicine, used both to treat active bacterial infections and to prevent infection in at-risk individuals. Depending on their mode of action they may either kill bacteria (bactericidal) or inhibit their growth (bacteriostatic). A small number also have antiprotozoal activity, such as metronidazole. Antibiotics are ineffective against viruses, which require antiviral drugs, and they also do not treat fungal infections, which are managed with antifungal medicines.
Although the term antibiotic is sometimes loosely used to describe any antimicrobial substance, its traditional meaning refers to compounds produced naturally by microorganisms to inhibit other microbes. Synthetic substances with similar antibacterial effects—such as sulfonamides—are classified as antibacterials but not technically as antibiotics. Both antibiotics and non-antibiotic antibacterials form the basis of antimicrobial chemotherapy.

Historical Background

Antibacterial substances have been used since antiquity. Many early cultures applied mouldy bread to infected wounds, with written references found in ancient Egypt, China, Nubia, Greece, Serbia and Rome. The first documented account of the medicinal use of moulds was recorded by the botanist John Parkinson in the seventeenth century.
The scientific development of antibacterials began in the late nineteenth century with the work of Paul Ehrlich, whose studies in Germany laid the foundations of synthetic antimicrobial therapy. Modern antibiotic therapy was transformed by Alexander Fleming’s discovery of penicillin in 1928 and its subsequent mass production, which revolutionised medical care during wartime. The first widely used synthetic antibacterial drug, Prontosil, was developed in the early 1930s in Germany.
The success and availability of antibiotics, however, has led to widespread misuse and overuse. As a result, many bacteria have developed resistance, reducing the effectiveness of formerly reliable treatments. Antimicrobial resistance is now considered a major global health threat, with millions of deaths each year associated with drug-resistant infections.

Etymology

The term antibiosis—meaning “against life”—was introduced in the nineteenth century to describe the inhibition of one microorganism by another. This phenomenon was later termed antibiotic by the microbiologist Selman Waksman, who initially applied the word to naturally produced substances effective at very low concentrations. Although Waksman’s definition excluded synthetic compounds, current usage is broader and includes any drug that kills or inhibits bacteria. The word derives from Greek roots meaning “against life”, while antibacterial comes from the Greek for “against rod-shaped organisms”, reflecting the appearance of some of the first bacteria studied.

Medical Uses

Antibiotics are used to treat or prevent bacterial infections and, in some cases, protozoan infections. When a patient presents with signs of infection but the exact pathogen is unknown, treatment often begins with empiric therapy using a broad-spectrum antibiotic. Once laboratory identification is available, a targeted therapy using a narrow-spectrum drug is preferred, which reduces toxicity, cost and the risk of promoting resistance.
Antibiotics are used to avoid surgery in selected conditions, such as uncomplicated acute appendicitis. They are also administered prophylactically to individuals at high risk of infection, including those with weakened immune systems, patients undergoing surgery and those requiring protection against certain dental or cardiac complications. They are widely used to prevent infection during episodes of severe neutropenia in cancer patients.
Antibiotics are not effective for preventing coronary heart disease and, in some cases, may even increase cardiovascular risks if used inappropriately.

Routes of Administration

Antibiotics can be administered via several routes. The most common is oral administration, suitable for mild to moderate infections. Severe or systemic infections may require intravenous therapy or injection to achieve rapid and effective drug concentrations.
Topical antibiotics are applied to accessible sites such as the eyes, ears or skin, where they can treat conjunctivitis, otitis externa, acne or cellulitis. Topical treatment achieves high local concentrations with minimal systemic exposure but may still cause allergic reactions or dermatitis. Dosing accuracy is also more difficult to control with topical applications.
In life-threatening infections, it is essential to administer antibiotics as quickly as possible, which is why emergency departments maintain immediate access to key treatments.

Global Consumption

Worldwide antibiotic consumption varies greatly. Observational data show that some countries have very high usage rates, whereas others use relatively little. Amoxicillin and its combinations are among the most widely consumed antibiotics globally. Variability in consumption reflects differences in disease burdens, prescribing practices, access to healthcare and regulatory oversight.

Side Effects

Although generally safe, antibiotics can cause a wide range of side effects that depend on the drug, the dose, the patient and the microbial target. Adverse effects range from mild gastrointestinal upset to severe allergic reactions, organ toxicity or disruption of normal microbial flora. Because of these risks—and the global threat of resistance—antibiotics must be prescribed judiciously.