How Many Classifications Do Antibiotics Have?

Antibiotics are designed to slow the growth of or kill bacteria. They are drugs that are derived from or chemically produced by microorganism like bugs, fungi or bacteria. They are just one class of antimicrobials, a larger group of drugs which also contains anti-fungal, anti-parasitic and anti-viral medications. There is a broad range of antibiotics, each with its own sets of usage and action mechanisms.

Classification of Antibiotics

The most effective classification is one derived from the chemical composition. Antibiotics with similar structural classes typically have comparable patterns of toxicity, effectiveness and allergic potential.

The main classifications are:

  • Beta-Lactams (Penicillin & Cephalosporin)
  • Macrolides
  • Fluroquinolones
  • Tetracycline
  • Aminoglycoside

Even though each class consists of a variety of drugs, each one is still unique in its own way.

1. Beta-Lactam Antibiotics


The eldest type of antibiotics is penicillin which shares a common chemical composition as cephalosporin. Generally bactericidal, penicillin hinders bacteria's ability to form their cell walls. This antibiotic is often used in cases of dental, skin, respiratory tract, ear, and urinary tract infections as well as gonorrhea.

The different types of penicillin are:

Natural penicillin

Founded on the unique penicillin-G structure, this type of antibiotics is used to fight staphylococci and streptococci gram-positive strains as well as gram-negative strains like meningococcus.

Penicillinase-resistant penicillin

Notably oxacillin and methicillin, this type of penicillin works even when exposed to bacterial molecules that typically deactivates natural penicillin.


Broad spectrum antibiotics like amoxicillin and ampicillin are used to fight a wider range of bacterial infections.


Cephalosporin is in the same classification of antibiotics as penicillin even though its chemical structure differs in several respects. They both have a structure that hinders the growth of bacterial cell walls. The main difference is cephalosporin is cephalosporium acremonium based.

Cephalosporin has a broad range of usage including the treatment of strep throat, pneumonia, tonsillitis, staph infections, skin infections, otitis media, kidney and bladder infections, bone infections and gonorrhea. Every time a new generation of cephalosporin emerges, it carries with it a broader spectrum of activity.

2. Fluoroquinolones

The newest classification of antibiotics is fluoroquinolones. A synthetic antibiotic, fluoroquinolones belong to the family of quinolones and are not derived from bacteria. Older forms of quinolones are mostly used to treat urinary tract infects as they were not well absorbed into the body's system. However, the newer versions are broad-spectrum bacteriocidal antibiotics that are easily absorbed into the body. Because of this, fluoroquinolones can be administered in both pill form or intravenously.

Fluoroquinolones work by inhibiting bacteria ability to produce DNA, making it difficult to reproduce. This antibiotic is mostly used to treat skin infections, urinary tract infection and respiratory infections like bronchitis and sinusitis.

3. Tetracycline

Having a chemical structure with four rings, tetracyclines are derived from a type of Streptomyces bacteria. They are broad-spectrum bacteriostatic antibiotics, effective against a multitude of microorganisms.

The most common use today for tetracyclines is the treatment of moderately severe rosacea and acne. They can also treat respiratory tract infections, sinus infections, intestinal infections, ear infections and urinary tract infections as well as Lyme disease, gonorrhea and Rocky Mountain spotted fever.

4. Macrolides

Obtained from the Streptomyces bacterium, macrolides are types of antibiotics that are bacteriostatic, thus inhibiting protein synthesis. The prototype of this class is erythromycin and is used similarly as penicillin. Newer versions like clarithromycin and azithromycin are used to treat respiratory tract infections because of their substantial ability to permeate the lung region. They are also used to treat gastrointestinal tract infections, genital infections and bacterial infections of the skin.

5. Aminoglycosides

Aminoglycosides are made from different Streptomyces species, which are derived from a fungus called Streptomyces griseus. They are bactericidal and stop bacteria from producing proteins.

This classification of antibiotics is used to fight gram-negative bacteria and can be used in combination with cephalosporin or penicillin. While they work well, bacteria can easily become resistant to aminoglycosides. They are given intravenously because the stomach breaks them down more easily. They are considered a short-term antibiotic.

Will There Be Any Side Effects?

Below is a table of the possible side effects of different types of antibiotics.

Mechanism of Action


Possible Side Effects

Beta-lactam antibiotics (Penicillin and Cephalosporin) inhibit bacterial cell wall production.

  • Ampicillin

  • Amoxicillin

  • Cefuroxime

  • Ceftriaxone

  • Ceforanide

  • Ceforperazone

  • Cefozopran

Common side effects of penicillin include diarrhea, nausea, upset stomach and vomiting. In very rare cases, individuals may have an allergic reaction.

In rare cases, cephalosporin results in nausea, mild stomach cramps and diarrhea. Individuals may experience an allergic reaction such as a skin rash or fever.

Macrolides hinder bacterial protein production

  • Erythromycin

  • Clarithromycin

  • Azithromycin

  • Dirithromycin

  • Roxithromycin

  • Troleandomycin

Possible side effects include nausea, vomiting and diarrhea. Rarely, a temporary auditory impairment may develop. In rare cases, there may be an allergic reaction. These symptoms would include anaphylaxis and dermatologic infections.

Fluoroquinolones prevent bacteria from producing DNA.

  • Ciprofloxacin

  • Levofloxacin

  • Lomefloxacin

  • Norfloxacin

  • Sparfloxacin

  • Clinafloxacin

  • Gatifloxacin

  • Ofloxacin

  • Trovafloxacin

Relatively safe and well tolerated, fluoroquinolones can cause several mild side effects, with the most common as vomiting, diarrhea, nausea and abdominal pain. Less common but more serious side effects include headache, confusion and dizziness, phototoxicity and convulsions.

Fluoroquinolones are classed as pregnancy category C.

Tetracyclines inhibit bacteria ability to produce protein.

  • Tetracycline

  • Doxycycline

  • Minocycline

  • Oxytetracycline

It's important to note tetracycline becomes toxic over time and can cause a dangerous syndrome leading to kidney damage. They should not be used in children under age 8 as they will interfere with tooth development.

Common side effects include cramps, diarrhea, sore tongue or mouth. Tetracyclines can also cause skin photosensitivity and sensitivity to sunlight. Rarely, a secondary intracranial hypertension will form accompanied by vision problems and a severe headache.

Aminoglycosides inhibit bacterial protein synthesis.

  • Amikacin

  • Gentamicin

  • Kanamycin

  • Neomycin

  • Streptomycin

  • Tobramycin

Aminoglycosides may cause irreversible toxic damage to the ear and hearing. Also, note aminoglycoside antibiotics may be nephrotoxic and cause kidney damage.

Recommended Usage

With knowledge of the classification of antibiotics, you should also pay attention to the safe using of the medication. Always follow the instructions or your doctor's advice.

  • To minimize chances of producing resistant strains of bacteria, antibiotics should only be prescribed when it is evident that a bacterial infection is present. Antibiotics should not be used to treat viral infections. Avoid the use of fluoroquinolones for less serious infections.
  • In the case of severe infections, it is recommended to start with a broad spectrum antibiotic and switch to a narrow spectrum drug as soon as the bacterial infection is identified.
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