Antibiotics Classification

Bacterial infections were and still are one of the biggest problems in the world, causing serious illnesses and even deaths every year. To fight these bacterial infections, antibiotics have become the most reliable defence mechanism of humankind, saving countless lives every year. However, with time, the bacteria have shown modifications in their genes to fight back this defence mechanism, which makes it essential to understand the classification of antibiotics. 

1.0Antibiotics Classification Definition

The Classification of antibiotics describes the way in which these medications are grouped according to their structure, mechanism of action, spectrum of activity, and type of bacteria they act on. This knowledge is crucial for choosing the right antibiotic to treat different infections effectively. Antibiotics are a central part of modern medicine, providing life-saving treatment for what would otherwise be fatal conditions.

2.0Working Principle of Antibiotics

Antibiotics work on different principles based on the target site and the process it follows to fight these disease-causing bacteria, which include: 

1. Inhibition of Cell Wall Synthesis: Antibiotics interfere with the synthesis of the cell wall of bacteria, which causes bacteria to lose their structural strength and integrity, which eventually causes them to die. 
2. Inhibition of Protein Synthesis: These antibiotics block the production of proteins in bacteria by making bonds with bacterial ribosomes. 
3. Inhibition of Nucleic Acid Synthesis: The antibiotics directly target the DNA replication or RNA synthesis in bacteria and prevent bacteria from multiplying. 
4. Disruption of Cell Membranes: Some antibiotics also damage the cell membrane of a bacteria, which makes it leaky and eventually cell death.  

3.0Classification of Antibiotics

Antibiotics can be classified in several ways, including their chemical structure, mechanism of action, spectrum of activity, and origin. Below is a detailed classification of antibiotics with examples: 

Chemical Classification of Antibiotics

The chemical structure of antibiotics is a key classifier among bathochromic drugs. Antimicrobials with a similar molecule structure generally have a shared mechanism of action. Some common chemical classifications include:

• Beta-lactam: Antibiotics classification: this group includes antibiotics with a β-lactam ring in their structure. They include Penicillins and Cephalosporins. 
• Tetracyclines: These are broad-spectrum antibiotics, including Doxycycline, Tetracycline, and Minocycline. 
• Fluoroquinolones: These are synthetic antibiotics with a fluoroquinolone ring structure. Examples include Ciprofloxacin, Levofloxacin, and Moxifloxacin. 
• Sulfonamides: These synthetic antibiotics block the folate analogue's production in bacteria. Examples include Sulfamethoxazole, often combined with Trimethoprim (Co-Trimoxazole). 
• Macrolides Antibiotics classification: This class has a characteristic macrocyclic lactone ring. Examples include Erythromycin, Azithromycin, and Clarithromycin.

Mechanism of Action Classification

Antibiotics can be categorised according to their mechanism of action, which is a mode of inhibition of bacterial growth. The major mechanisms of action are as follows: 

• Cell Wall Synthesis Inhibitors: These antibiotics inhibit the synthesis of bacterial cell walls. Thus, it causes cell death. Examples include Penicillins, Cephalosporins, and Vancomycin. 
• Protein Synthesis Inhibitors: These antibiotics fill the vacuoles on bacterial ribosomes, thus preventing protein synthesis and, consequently, bacterial growth. Examples include Aminoglycosides (Gentamicin), Macrolides (Erythromycin), Tetracyclines (Doxycycline), 
• Nucleic Acid Synthesis Inhibitors: These antibiotics block the DNA or RNA synthesis of bacteria. Examples include Fluoroquinolones (Ciprofloxacin), Rifamycins (Rifampin), 
• Folate Synthesis Inhibitors: These antibiotics inhibit the bacterial ability to synthesise folic acid, an essential nutrient. Examples include Sulfonamides (Sulfamethoxazole) and Trimethoprim 

Spectrum of Activity

Antibiotics are also grouped according to their activity spectrum, i.e., the number of bacteria which can be successfully treated. The spectrum can be classified as: 

• Narrow-spectrum Antibiotics Classification: These are potent against a defined spectrum of bacteria. They are useful for the treatment of infections with a pathogenic agent. Examples include Penicillin G (effective against Gram-positive bacteria) and isoniazid (used for treating tuberculosis). 
• Broad-spectrum Antibiotics Classification: These antibiotics are active against a broad spectrum of bacteria, including Gram-positive and Gram-negative. They are frequently used when the infecting specific pathogen is unknown or involved in polymicrobial infection. Examples include Amoxicillin (broad-spectrum penicillin), Tetracyclines, and Ciprofloxacin (a fluoroquinolone). 
• Extended-spectrum Antibiotics Classification: These are adaptations of broad-spectrum antibiotics effective on a wide range of organisms, some of which may be resistant, meaning that they deal with the elimination of a wide representation of pathogenic bacteria rather than the damage of one specific strain (or class of strains). Examples include Extended-spectrum cephalosporins like Ceftriaxone and Ceftazidime. 

Antibiotics Based on Source 

Antibiotics can also be categorised based on the source of their origin, which includes: 

• Natural Antibiotics: These antibiotics are natural products of microorganisms, such as bacteria and fungi. Examples include Penicillins (from Penicillium fungi) and Streptomycin (from Streptomyces bacteria). 
• Semisynthetic Antibiotics: These are chemically altered forms of natural antibiotics to enhance the effect and/or circumvent resistance. Examples include Amoxicillin (a semisynthetic derivative of penicillin), Cephalexin (derived from cephalosporin), 
• Synthetic Antibiotics: These are the antibiotics which are completely synthesised chemically in laboratories. Examples include Sulfonamides and fluoroquinolones. 

4.0Antibiotic Resistance

Antibiotic resistance is becoming the biggest threat to global health. It occurs when bacteria develop the ability to resist the efforts of drugs that were once used to kill or stop their growth. The resistance of bacteria can develop over time with irregular or incomplete course of antibiotics. Reasons for resistance to these antibiotics can be: 

1. Enzyme Production: There are bacteria which can produce enzymes that have the power to break down the antibiotic before it can even start to work properly. 
2. Alteration of Target Sites: Some Bacteria can also mutate or alter the target site for antibiotics, which causes the drug to be ineffective. 
3. Efflux Pumps: Bacteria which have specialised pump-like projections that can effectively expel the antibiotic from the cell, which prevents it from working. 
4. Reduced Permeability: Some bacteria have the power to change the structure of cell membranes, which results in reduced ability of antibiotics to enter the cell.