Antibiotics Classification, Mechanism of Action, Brand Generics and Mnemonics

Antibiotics Classification

Antibiotics are categorized based on their core chemical structure, which determines their mechanism of action, spectrum of activity, and resistance profiles.

The chemical structure of an antibiotic dictates its target interaction, spectrum, and resistance mechanisms. Understanding these structural classes helps in drug design, resistance management, and combination therapy strategies.

Below is a detailed breakdown of the primary classification systems:

1. Classification by Chemical Structure

Antibiotics with similar structures often share mechanisms of action and resistance profiles.

Chemical Class	Examples	Key Feature
β-Lactams	Penicillins, Cephalosporins, Carbapenems	Contain a β-lactam ring; inhibit cell wall synthesis.
Aminoglycosides	Gentamicin, Amikacin	Amino sugars; bind 30S ribosomal subunit.
Tetracyclines	Doxycycline, Minocycline	Four-ring structure; block 30S ribosomal subunit.
Macrolides	Azithromycin, Clarithromycin	Macrocyclic lactone ring; inhibit 50S subunit.
Fluoroquinolones	Ciprofloxacin, Levofloxacin	Synthetic; inhibit DNA gyrase/topoisomerase.
Sulfonamides	Sulfamethoxazole, Trimethoprim	Folate synthesis inhibitors (PABA analogs).
Glycopeptides	Vancomycin, Teicoplanin	Large molecules; disrupt cell wall (Gram+).
Oxazolidinones	Linezolid	Synthetic; bind 50S ribosomal subunit.

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2. Classification by Mechanism of Action

Antibiotics target specific bacterial processes:

Mechanism	Drug Classes	Effect
Cell Wall Synthesis Inhibitors	β-Lactams, Glycopeptides, Fosfomycin	Cause bacterial lysis.
Protein Synthesis Inhibitors	Aminoglycosides, Macrolides, Tetracyclines	Block ribosomes (30S/50S).
Nucleic Acid Synthesis Inhibitors	Fluoroquinolones, Rifampin	Target DNA/RNA enzymes.
Folate Pathway Inhibitors	Sulfonamides, Trimethoprim	Block nucleotide synthesis.
Cell Membrane Disruptors	Polymyxins (e.g., Colistin)	Damage bacterial membranes.

3. Classification by Bacterial Target (Gram Stain)

Target	Antibiotics	Coverage
Gram-Positive	Vancomycin, Clindamycin, Oxacillin	Staphylococci, Streptococci
Gram-Negative	Aztreonam, Polymyxins, Ceftazidime	E. coli, Pseudomonas
Anaerobes	Metronidazole, Clindamycin	Bacteroides, Clostridium
Atypicals	Macrolides, Tetracyclines	Mycoplasma, Legionella

4. Classification by Spectrum of Activity

(a) Narrow-Spectrum

Target specific bacteria (Gram+ or Gram-).

Examples:

Penicillin G (Gram+ cocci).
Vancomycin (Gram+ MRSA).

(b) Broad-Spectrum

Target both Gram+ and Gram- bacteria.

Examples:

Tetracyclines, Fluoroquinolones, Carbapenems.

(c) Extended-Spectrum

Cover Pseudomonas, anaerobes, or drug-resistant strains.

Examples:

Piperacillin-tazobactam (Pseudomonas + anaerobes).
Ceftazidime (ESBLs).

5. Classification by Route of Administration

Oral: Amoxicillin, Ciprofloxacin.
IV/IM: Vancomycin, Meropenem.
Topical: Neomycin, Mupirocin.

6. Classification by Origin

Natural: Penicillin (from Penicillium mold), Streptomycin (from Streptomyces).
Semi-synthetic: Amoxicillin, Ceftriaxone.
Synthetic: Fluoroquinolones, Sulfonamides.

Penicillin Antibiotics

Chemical Class	Brand Name	Generic Name	Mechanism of Action	Mnemonics
Penicillins	Amoxil	Amoxicillin	Inhibit cell wall synthesis (peptidoglycan cross-linking)	“PENs Write On Bacteria Walls.” PENicillins = inhibit cell wall synthesis
	Principen, Omnipen	Ampicillin
	Augmentin	Amoxicillin-clavulanate
	Pen V K	Penicillin V potassium
Ending in ___cillin is a penicillin

Macrolides Antibiotics

Chemical Class	Generic Name	Brand Name	Mechanism of Action	Mnemonics
Macrolides	Azithromycin	Zithromax, Z-Pak	Inhibit protein synthesis (bind 50S ribosomal subunit)	ACE your Macrolide exam!” Azithromycin Clarithromycin Erythromycin
	Clarithromycin	Biaxin
	Erythromycin	Ery-Tab, Erythrocin, E.E.S.
Ending in ___mycin is grouped as an Macrolides or Erythromycins

Antibiotic Tetracycline

Chemical Class	Generic Name	Brand Name	Mechanism of Action	Mnemonics
Tetracyclines (TCN)	Doxycycline	Vibramycin	Inhibit protein synthesis (bind 30S ribosomal subunit)	“Tetra = 4 wheels = Stops protein machine.”
	Tetracycline	Sumycin, Tetracyn
	Minocycline	Minocin
Take on an empty stomach Avoid Sun Exposure (Photosensitivity Risk) Avoid with dairy and Antacids (binds with calcium) Tetracyclines are Fatal if expired, never take expired drug Tooth discoloration (avoid in pregnancy & children <8 years old)

Quinolones Antibiotics

Antibiotic Class	Generation	Generic Name	Brand Name	Mechanism of Action	Mnemonics
Quinolones	1st Generation	Nalidixic acid	Discontinued	Inhibit bacterial DNA gyrase and topoisomerase IVBlocks DNA replication.	“Fluoro = Flow of DNA stopped.” Block DNA gyrase (DNA replication)
Fluoroquinolones	2nd Generation	Ciprofloxacin	Cipro, Ciproxin
		Ofloxacin	Floxin, Ocuflox
		Norfloxacin	Noroxin
	3rd Generation	Levofloxacin	Levaquin, Iquix
	4th Generation	Moxifloxacin	Avelox, Vigamox
	4th Generation	Gemifloxacin	Factive

Take with water only
Avoid dairy, antacids, or calcium-fortified juices
Photosensitivity (sunburn risk)

Antibiotic Cephalosporin

Antibiotic Class	Generation	Generic Name	Brand Name	Mechanism of Action	Mnemonics
Cephalosporins	1st Generation	Cefazolin	Ancef, Kefzol	Inhibit cell wall synthesis, similar to penicillins. Bind to penicillin-binding proteins (PBPs) → disrupt bacterial cell wall synthesis → cause cell lysis	“CEF the chef cooks in 5 generations.” All start with CEF (e.g., Ceftriaxone, Cephalexin) 5 generations: each with broader Gram-negative coverage.
	1st Generation	Cephalexin	Keflex
	2nd Generation	Cefuroxime	Ceftin, Zinacef
		Cefoxitin	Mefoxin
		Cefaclor	Ceclor
	3rd Generation	Ceftriaxone	Rocephin
		Cefotaxime	Claforan
		Ceftazidime	Fortaz, Tazicef
		Cefdinir	Omnicef
	4th Generation	Cefepime	Maxipime
	5th Generation	Ceftaroline	Teflaro
	5th Generation	Ceftobiprole	Zevtera

Class: β-Lactam antibiotics (structurally similar to penicillins)
All starts with Cef______
Photosensitivity (sunburn risk)

Sulfonamides Antibiotics

Chemical Class	Generic Name	Brand Name	Mechanism of Action	Mnemonics
Sulfonamides	Sulfamethoxazole + Trimethoprim	Bactrim, Septra	Inhibit folic acid synthesis (DNA synthesis)	“Sulfa drugs STOP Folic acid.” Inhibit folic acid → block DNA synthesis
	Sulfasalazine	Azulfidine
	sulfisoxazole	Gantrisin

Be hydrated, drink enough water, else Crystalluria (Kidney Damage)
Risk of Sun Sensitivity (Photosensitivity)”

aminoglycosides antibiotics

Chemical Class	Generic Name	Brand Name	Mechanism of Action	Mnemonics
Aminoglycosides	Gentamicin	Garamycin, Genoptic	Inhibit protein synthesis cause mRNA misreading	“A Mean GNATS can’t hear.” G = Gentamicin N = Neomycin A = Amikacin T = Tobramycin S = Streptomycin Side effect: ototoxicity + nephrotoxicity
	Neomycin	Neo-Fradin, Myciguent
	Amikacin	Amikin
	Tobramycin	Tobrex, Bethkis, TOBI
	Streptomycin	Streptomycin

aminoglycosides antibiotics

Nitroimidazoles are a structurally distinct class of antimicrobials defined by their 5-nitroimidazole core, with selective toxicity against anaerobes and protozoa. Their mechanism relies on nitro group reduction, making them irreplaceable for treating certain infections. Nitroimidazole Antibiotic (not a typical antibacterial like β-lactams or macrolides).

Mechanism of Action:
The nitro group is reduced in anaerobic bacteria/protozoa, producing toxic intermediates that damage DNA.
Only active against anaerobic bacteria & certain parasites (not aerobic bacteria).

Antibiotic Class	Generic Name	Brand Name	Mechanism of Action	Important
Nitroimidazoles	Metronidazole	Flagyl	The nitro (–NO₂) group on the imidazole ring is reduced by microbial enzymes (nitroreductases), Causes DNA strands to breaks, disrupts microbial nucleic acids, then cell death	NO alcohol (beer, wine, liquor, mouthwash, cough syrup) during treatment and for ≥3 days after finishing. Common: Metallic taste, nausea, dark urine (harmless). Take with food to reduce stomach upset.

Antibiotics Classification, Mechanism of Action, Brand Generics and Mnemonics

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