Antibiotics - Classification, Applications in Detail - Imdip

In this article, we discussed all types of antibiotics and their classifications.

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Antibiotics are classified according to their mechanism of action and spectrum of activity.

Antibiotics and their classifications, applications in detail.

Beta-Lactam Antibiotics

Beta-lactam antibiotics are effective against Gram-positive and some Gram-negative bacteria.

Mechanism of action: It inhibits the cell wall synthesis of bacterial cells. So it can't grow and multiply itself.

Names of Beta-Lactam Antibiotics:

• Penicillins
• Amoxicillin
• Ampicillin
• Penicillin G & V
• Piperacillin (often combined with Tazobactam)

Cephalosporin Antibiotics (5 Generations) 

• 1st Gen: Cephalexin, Cefazolin
• 2nd Gen: Cefuroxime, Cefaclor
• 3rd Gen: Ceftriaxone, Ceftazidime
• 4th Gen: Cefepime
• 5th Gen: Ceftaroline (active against MRSA)

Carbapenems

Broad-spectrum, used for drug-resistant infections

• Imipenem
• Meropenem
• Ertapenem

Monobactams (Gram-negative coverage)

• Aztreonam

Macrolides

Mechanism of action: These types of antibiotics work by inhibiting protein synthesis by binding to the 50S ribosomal subunit in bacterial cells.

Good alternative for penicillin-allergic patients.

Example of Macrolides:

• Azithromycin
• Clarithromycin
• Erythromycin

Application of Macrolides:

These antibiotics are used for respiratory infections, skin infections for acne, Lyme disease, and atypical infections.

Tetracyclines

Tetracyclines are Broad-spectrum antibiotics.

Mechanism of action:They work by inhibiting protein synthesis by binding to the 30S ribosomal subunit in bacterial cells.

Example of Tetracyclines:

• Doxycycline
• Tetracycline
• Minocycline

Application of Tetracyclines:

used for acne, Lyme disease, and atypical infections.

Fluoroquinolones

Fluoroquinolones are generally considered a broad-spectrum class of antibiotics. They are effective against a wide range of bacterial species, including both Gram-positive and Gram-negative bacteria.

Mechanism of action: These types of antibiotics work by inhibiting DNA replication in bacterial cells. They primarily target two key bacterial enzymes, DNA gyrase and Topoisomerase IV.

• DNA gyrase (also known as topoisomerase II): Mainly in Gram-negative bacteria.
• Topoisomerase IV: Mainly in Gram-positive bacteria.

Example of fluoroquinolones:

• Ciprofloxacin
• Levofloxacin
• Moxifloxacin
• Delafloxacin
• Gemifloxacin
• Norfloxacin
• Oflaxacin
• Gatifloxacin (Available only as eye drops in the United States, Canada due to severe blood sugar abnormalities.)
• Grepafloxacin (Withdrawn globally, due to heart rhythm issues)
• Trovafloxacin (Withdrawn globally, including the United States and European Union, for systemic use due to liver toxicity)
• Temafloxacin (Withdrawn globally due to its allergic reactions, hemolytic anemia, and kidney problems.)

Application of fluoroquinolones:

These types of antibiotics are commonly used for urinary tract infections (UTIs) and Respiratory tract infections.

Aminoglycosides

Mechanism of action: Aminoglycoside antibiotics work by inhibiting protein synthesis by binding to the 30S ribosomal subunit in bacterial cells. Normally used for serious Gram-negative infections.
But you should know that they may cause nephrotoxicity (kidney damage) & ototoxicity (hearing loss) in some cases.

Example of Aminoglycosides:

• Gentamicin
• Amikacin
• Tobramycin

Application of Aminoglycosides:

These are used in the treatment of sepsis, pneumonia, urinary tract infections, and intra-abdominal infections caused by bacteria.

They are combined with beta-lactam antibiotics (like penicillin or vancomycin) for serious Gram-positive infections such as Endocarditis caused by Enterococcus, Staphylococcus, or Streptococcus species.

Sulfonamides (Inhibit folic acid synthesis)

Used for UTIs, MRSA infections, and respiratory infections

• Sulfamethoxazole + Trimethoprim (Co-trimoxazole / Bactrim)

Lincosamides

Mechanism of action: Lincosamide antibiotics inhibit protein synthesis by binding to the 50S ribosomal subunit in bacterial cells.

Example of Lincosamide antibiotics:

• Clindamycin
• Lincomycin

Application of Lincosamide:

Normally used for skin infections, dental infections, and anaerobic bacteria.

Glycopeptides

Mechanism of action: These antibiotics work by inhibiting cell wall synthesis.

Example of Glycopeptide antibiotics:

• Vancomycin
• Teicoplanin

Application of Glycopeptide:

Used for MRSA and drug-resistant Gram-positive infections

Oxazolidinones

Oxazolidinone antibiotics inhibit protein synthesis - 50S ribosome

Example of Lincosamide antibiotics:

• Linezolid
• Tedizolid

 

Application of Lincosamide:

Used for drug-resistant Gram-positive infections (MRSA, VRE)

Nitroimidazoles

Nitroimidazole antibiotics are primarily known for their effectiveness against anaerobic bacteria and certain protozoa.

Mechanism of action: These antibiotics work by causing DNA damage.

 

Example of Nitroimidazole antibiotics:

• Metronidazole (most widely used)
• Tinidazole
• Secnidazole
• Ornidazole

Application of Nitroimidazoles:

Used for anaerobic infections, H. pylori, and protozoal infections

Polymyxins

Mechanism of action: These antibiotics work by disrupting bacterial cell membranes.

Example of Polymyxin antibiotics:

• Colistin (Polymyxin E)
• Polymyxin B

Application of Polymyxins:

Used for multidrug-resistant Gram-negative bacteria

Rifamycins

Mechanism of action: Inhibits RNA synthesis

Example of Rifamycin antibiotics:

• Rifampin
• Rifabutin

Application of Rifamycins:

This type of antibiotic is used for tuberculosis (TB) and meningitis prophylaxis.

Another way to look at them:

• Gram-positive infections: Penicillins, Cephalosporins, Macrolides, Oxazolidinones
• Gram-negative infections: Fluoroquinolones, Aminoglycosides, Polymyxins
• Anaerobic infections: Metronidazole, Clindamycin
• Atypical infections (Mycoplasma, Chlamydia, Legionella): Tetracyclines, Macrolides, Fluoroquinolones
• Resistant infections (MRSA, VRE, MDR bacteria): Linezolid, Vancomycin, Colistin