antibiotics

CLASSIFICATION

OF ANTIBIOTICS



Khalid Mehmood

(2005-va-54)

M.Phil (Clinical Medicine)

ANTIBIOTICS CLASSIFICATION

 What are Antibiotics?

The word "antibiotics" comes from the Greek anti

("against") and bios ("life"). Antibiotics are drugs

that either destroy bacteria or prevent their

reproduction. Antibiotics that kill bacteria are

called "bactericidal" and the ones that stop the

growth of bacteria are called "bacteriostatic".

ANTIBIOTICS CLASSIFICATION

The main classes of antibiotics are:



 Beta-Lactams

 Penicillins

 Cephalosporins

 Macrolides



 Quinolones



 Tetracyclines



 Aminoglycosides



 Sulphonamides

ANTIBIOTIC TARGETS IN BACTERIAL

CELLS

Class Mechanism of action Examples



Penicillins

Penicillin G



Amoxicillin

B-lactam antibiotics

Flucloxacillin

Penicillins

Inhibit bacterial cell wall synthesis

Cephalosporins

Cephalosporins

Cefoxitin



Cefotaxime



Ceftriaxone



 Erythromycin



Macrolides Inhibit bacterial protein synthesis  Azithromycin



 Clarithromycin

 Tetracycline



 Minocycline

Tetracyclines Inhibit bacterial protein synthesis

 Doxycycline



 Lymecycline

 Gentamicin

Aminoglycosides Inhibit bacterial protein synthesis

 Amikacin

 Norfloxacin



 Ciprofloxacin

Quinolones Inhibit bacterial DNA synthesis

 Enoxacin



 Ofloxacin

 Co-trimoxazole

Blocks bacterial cell metabolism by inhibiting

Sulphonamides

enzymes  Trimethoprim

PENICILLINS (BACTERICIDAL)

 In 1929 Alexander Fleming inadvertently

discovered penicillin.

 Fleming eventually extracted the compound from

the mold that had been responsible for

destruction of the bacterial colonies.

 The product was named penicillin

Mode of Action

 All bacterial cells have a cell wall that protects

them.

 Penicillins (beta-lactam antibiotics) work by

interfering with interpeptide linking of

peptidoglycan, the a strong, structural molecule

found specifically bacterial cell walls.

PENICILLINS (BACTERICIDAL)

Antimicrobial Spectrum of Penicillins

 Penicillins have a bacteriocidal effect on Gram-

positive bacteria.

 In Gram-positive cells, peptidoglycan makes up

as much as 90% of the thick, compact cell wall,

and is the outermost layer.

 Penicillins are not effective against Gram-

negative bacteria,

 Peptidoglycan is not the outermost layer, but

that lies between the plasma membrane and a

lipopolysaccharide (LPS) outer membrane.

 Penicillin cannot access the peptidoglycan of

Gram-negative cells.

PENICILLINS (BACTERICIDAL)

 Penicillins antibiotics are:

 Penicillins-G

 Penicillins-V

 Ampicillin

 Amoxycillin

 Naficillin

 Methicillin

 Flucloxacillin

 Phenethicillin

 Cloxacillin

 Oxacillin

CEPHALOSPORINS (BACTERICIDAL)

 Cephalosporin compounds were first isolated

from cultures of Cephalosporium acremonium

Mode of action

 Cephalosporins have a mechanism of action

identical to that of the penicillins.

 Like the penicillins, cephalosporins have a beta-

lactam ring structure that interferes with

synthesis of the bacterial cell wall

 Cephalosporins disrupt the synthesis of the

peptidoglycan layer of bacterial cell walls, which

causes the walls to break down and eventually

the bacteria die.

CEPHALOSPORINS (BACTERICIDAL)

 Cephalosporins are among the most diverse

classes of antibiotics, they are grouped into

"generations" by their antimicrobial properties.

Each newer generation has a broader spectrum of

activity than the one before.

 The first generation cephalosporins:They

possess generally excellent coverage against most

gram-positive pathogens cephalothin

 cefazolin

 cephapirin

 cephradine

 cephalexin

 cefadroxil

CEPHALOSPORINS (BACTERICIDAL)

 The second generation cephalosporins. In

addition to the gram positive spectrum of the

first generation cephalosporins, these agents

have expanded gram negative spectrum. The

second generation includes:

 cefaclor

 cefamandole

 cefonicid

 ceforanide

 cefuroxime

CEPHALOSPORINS (BACTERICIDAL)

 The third generation cephalosporins have much

expanded gram negative activity. However, some members

of this group have decreased activity against gram-positive

organisms. The third generation includes:

 cefcapene

 cefdaloxime

 cefditoren

 cefetamet

 cefixime

 cefmenoxime

 cefodizime

 cefoperazone

 cefotaxime

 cefpimizole

 cefpodoxime

 Ceftibuten

 ceftriaxone

CEPHALOSPORINS (BACTERICIDAL)

 The fourth generation cephalosporins are

extended-spectrum agents with similar activity

against gram-positive organisms as first-generation

cephalosporins. They also have a greater resistance to

beta-lactamases than the third generation

cephalosporins. Many fourth generation

cephalosporins can cross blood brain barrier and are

effective in meningitis. The fourth generation

includes:

 cefclidine

 cefepime

 cefluprenam

 cefozopran

 cefpirome

 cefquinome

QUINOLONES (BACTERICIDAL)

 Quinolones (fluoridated quinolones) are the

newest class of antibiotics. Their generic name

often contains the root "floxacin". They are

synthetic antibiotics, and not derived from

bacteria.

 a. Mode of action

These antimicrobials bind to the A subunit of

DNA gyrase (topoisomerase) and prevent

supercoiling of DNA, thereby inhibiting DNA

synthesis.

 b. Spectrum of activity

These antibiotics are active against Gram-

positive cocci and are used in urinary tract

infections

QUINOLONES (BACTERICIDAL)

 Quinolones are used to treat most common urinary tract

infections, skin infections, and respiratory infections (such

as sinusitis, pneumonia, bronchitis).

 Quinolone grope includes:

 ciprofloxacin

 levofloxacin

 Lomefloxacin

 nalidixic acid

 oxolinic acid

 norfloxacin

 sparfloxacin

 clinafloxacin

 gatifloxacin

 ofloxacin

 trovafloxacin

TETRACYCLINES (BACTERIOSTATIC)



 Tetracyclines got their name because they share

a chemical structure that has four rings. They

are derived from a species of Streptomyces

bacteria.

 a. Mode of action

The tetracyclines reversibly bind to the 30S

ribosome and inhibit binding of aminoacyl-t-RNA

to the acceptor site on the 70S ribosome.

 b. Spectrum of activity

These are broad spectrum antibiotics and are

useful against intracellular bacteria

TETRACYCLINES (BACTERIOSTATIC)

 Tetracyclines are used in the treatment of

infections of the respiratory tract, sinuses, middle

ear, urinary tract, skin, intestines.

 Tetracycline antibiotics are:



 tetracycline



 doxycycline



 minocycline



 oxytetracycline

MACROLIDES (BACTERIOSTATIC)

 The macrolide antibiotics are derived from

Streptomyces bacteria, and got their name

because they all have a macrocyclic lactone

chemical structure.

 a. Mode of action

The macrolides inhibit translocation of the

peptidyl tRNA from the A to the P site on the

ribosome by binding to the 50S ribosomal 23S

RNA.

 b. Spectrum of activity

Gram-positive bacteria, Mycoplasma, Legionella

 Macrolide antibiotics are used to treat

respiratory tract infections (such as pharyngitis,

sinusitis, and bronchitis), genital,

gastrointestinal tract, and skin infections.

MACROLIDES (BACTERIOSTATIC)

Macrolide antibiotics are:

 erythromycin



 clarithromycin



 azithromycin



 dirithromycin



 roxithromycin



 troleandomycin

AMINOGLYCOSIDES (BACTERICIDAL)

 Aminoglycosides are derived from various species

of Streptomyces

 Aminoglycoside antibiotics are used to treat

infections caused by gram-negative bacteria.

Aminoglycosides may be used along with

penicillins or cephalosporins to give a two-

pronged attack on the bacteria.

 a. Mode of action

The aminoglycosides irreversibly bind to the 30S

ribosome and freeze the 30S initiation complex

(30S-mRNA-tRNA), so that no further initiation

can occur. The aminoglycosides also slow down

protein synthesis that has already initiated and

induce misreading of the mRNA.

AMINOGLYCOSIDES (BACTERICIDAL)

 b. Spectrum of Activity

Aminoglycosides are active against many gram-

negative and some gram-positive bacteria. They

are not useful for anaerobic bacteria,

 d. Synergy

The aminoglycosides synergize with β-lactam

antibiotics such as the penicillins. The β-lactams

inhibit cell wall synthesis and thereby increase

the permeability of the bacterium to the

aminoglycosides.

AMINOGLYCOSIDES (BACTERICIDAL)

Aminoglycoside grope includes:

 amikacin



 gentamicin



 kanamycin



 neomycin



 streptomycin



 tobramycin

Sulphonamides (Bacteriostatic)

 Sulfonamide drugs were the first antimicrobial

drugs, and paved the way for the antibiotic

revolution in medicine.

 The first sulfonamide, trade named red dye

Prontosil, was actually a prodrug.

 It was later proved by French researchers that

the active agent of Prontosil was sulfanilamide,

or para-aminobenzenesulfonamide, a product of

the body’s metabolism of Prontosil.

 By the 1940s sulfanilamide was a widely used

drug.

Sulphonamides (Bacteriostatic)

 Mechanism of action

 Sulphonamides are structural analogs of PABA.

They compete with PABA for enzyme

dihydropteroate synthetase (DHPS), which is

essential for synthesis of

folic acid in bacteria.

 Folate is required for synthesis of precursors of

DNA and RNA in bacteria

Sulphonamides (Bacteriostatic)

 Sulfonamide Antibiotics includes

 sulfadiazine



 sulfamethoxazole



 sulfasalazine



 sulfisoxazole



 sulfacetamide



 sulfanilamide



 sulfathiazole



 sulfabenzamide