Antibiotics

 For More details

• Mechanism of action of B-lactam antibiotics

1)  Penicillins  (Same MOA)

2)  Cephalosporins

3)   B-lactamase inhibitors (help to increase Penicillins and Cephalosporins potency)

4)    Monobactams (Almost same as Penicillin.)

 

All B-lactam antibiotics are bactericidal which give their action by inhibiting the syntheis of cell wall action which cause lysis of bacteria.

 

• How cell wall formed --??

Cell wall is made up with two components.

Sugar backbones (glycone) + Peptide chain

       (monosaccharide)                   (short chain of amino acids)

 

       NAG                       Peptidoglycon

       NAM                       (highly porass)

 

 

 

 

Now, All bacteria are hyper osmotic means they absorb water inside cytoplasmic region. Due to this bacteria swell and they have a chance to burst, but cell wall is strong and rigid which provide protection. against this.

 

 

 

 

Now, when B-lactam antibiotics introduced into body  they bind with Penicillin Binding proteins (PRPs).

which inhibits the action of enzymes (transpeptidas )  and inhibit the synthesis of cell wall.

which causes the lysis and cell death of bacteria.

 

 

 

# PBPs vary in their affinity for binding penicillin or other B-lactam antibiotics.

 

 

Penicillins

 

It is the first antibiotic, which was first discovered and in reporte 1929 by Sir Alexander fleming.

 

 

 

 

• All penicillin composed of the

 6-amino penicillinic acid nucleus with side chain.

 B-lactam ring     Thiazolidine ring    determines the antibacterial spectrum + p'cological properties.

Commercial production of biosynthetic penicillin depends on Penicillium notatum and Penicillium Chrysogenum.

Semi-synthetic penicillin are widely used. because they are revistance to stomach acid. so they can be taken orally and also they have a digree of resistance to Penicillinase.

Penicillinase:A penicillin-destroying enzyme which is produced by some bacteria.

 

Cephalosporins

These are the second major group of B-lactam antibiotics because they also Contain B-lactam ring.

History

Cephalosporins were firstly isolated by Guiseppe Brotzy in 1945 from the fungus Cephalosporium acremonium which inhibited the growth of wide varities of gram-positive and gram-negative bacteria.

He noticed that these cultures produced substance where effective against salmonella typhi, which cause typhoid fever.

Cephalosporins are closly related to the penicilling in both structul and mode of action and are used to treat bacterial infections. (identical moa)

 

Cephalosporins mostly obtained from Cephalosporin

Cephalosporins contain a B-lactam ring which is fused with 6-mumbered dihydrothiazine ring.

Cephalosporins contain 7-aminocephalosporanic acid                                    (7-ACA) nucleus and side chain.

B-lactam ring dihydrothiazine ring          • affinity for PBP....

                                                                          • resistance to locamasy..

 

 

 

 

Chemical structure

1. Sulfonamides and related drugs: Sulfadiazine and others, Sulfones Dapsone(DDS), Paraaminosalicylic acid (PAS).

2. Diaminopyrimidines: Trimethoprim, Pyrimethamine.

3. Quinolones: Nalidixic acid, Norfloxacin, Ciprofloxacin, Prulifloxacin, etc.

4. β-Lactam antibiotics: Penicillins, Cephalosporins, Monobactams, Carbapenems.

5. Tetracyclines: Oxytetracycline, Doxy-

cycline, etc.

6. Nitrobenzene derivative: Chloramphenicol.

7. Aminoglycosides: Streptomycin, Gentamicin, Amikacin, Neomycin, etc.

8. Macrolide antibiotics: Erythromycin,Clarithromycin, Azithromycin, etc.

9. Lincosamide antibiotics: Lincomycin,Clindamycin.

10. Glycopeptide antibiotics: Vancomycin, Teicoplanin.

11. Oxazolidinone: Linezolid.

12. Polypeptide antibiotics: Polymyxin-B, Colistin, Bacitracin, Tyrothricin.

13. Nitrofuran derivatives: Nitrofurantoin,Furazolidone.

14. Nitroimidazoles: Metronidazole, Tinidazole, etc.

15. Nicotinic acid derivatives: Isoniazid, Pyrazinamide, Ethionamide.

16. Polyene antibiotics: Nystatin, Amphotericin-B, Hamycin.

17. Azole derivatives: Miconazole, Clotrimazole, Ketoconazole, Fluconazole.

18. Others: Rifampin, Spectinomycin, Sod.fusidate, Cycloserine, Viomycin, Ethambutol, Thiacetazone, Clofazimine, Griseofulvin.

 

 

B. Mechanism of action

1. Inhibit cell wall synthesis: Penicillins, Cephalosporins, Cycloserine, Vancomycin,Bacitracin.

2. Cause leakage from cell membranes:Polypeptides Polymyxins, Colistin, Bacitracin. Polyenes Amphotericin B, Nystatin, Hamycin.

3. Inhibit protein synthesis: Tetracyclines, Chloramphenicol, Erythromycin, Clindamycin, Linezolid.

4. Cause misreading of m-RNA code and affect permeability: Aminoglycosides,Streptomycin, Gentamicin, etc.

 

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