BASICS OF ANTIBIOTICS

Dr.Muhammad Jahangir Veterinary Officer Health Bhowana (Jhang)

Tel:00-92-300-7701465, 00-92-345-7701465. drjahangir23@yahoo.com

Micro-organisms are minute living organisms usually of microscopic size and are abundant in our environment, living in soil, air feed, water & also inside the body of the animal.

Bacteria are representative of pathogenic micro-organisms consisting of a single cell. They have cell wall & multiply by self division. These may be classified as Gram positive & Gram negative bacteria based on their response to Gram’s Method of staining.

Antibiotics are substances produced by living tissue such as fungi, mould or bacteria that inhibit the growth of other micro-organisms. Some antibiotics have been synthesized & new compounds developed by slightly changing the original formula. Antibiotics are produced in three ways i.e.

1. Fermentation e.g. Penicillin tetracycline, erythromycin etc.
2. Semi-synthesis e.g. Ampicilline, Kanamycin etc.
3. Synthesis e.g. Choloromphenicol, Fosfomycin etc.

The activity of antimicrobial agent involves three factors i.e. the antibiotic, the causal organism of the disease and the animal, bird being treated (host).The administration of drugs, therefore, should take into consideration all the three factors. Some of the important points relating to each of three factors are given below:

Host:    Age. Site of infection, severity of infection, Complications of disease.  

Causal organism: Kind of organism, resistant or sensitive, single or mixed.       

Drug: Bactericidal or Bacteriostatic, absorption, Excretion, dosage, stability, toxicity, route of administration etc.

Based on the typical characteristics like toxicity & antimicrobial spectrum etc, antibiotics are classified as under:

Aminoglycosides          e.g. Streptomycin, Neomycin, Gentamicin, Kanamycin etc.

Cephalosporin               e.g. Cephalosporadine, Cephalothin, Cephradine, Ceftazole etc.

Chloromphenical           e.g. Chloromphenical etc.

Glycopeptide                e.g. Vancomycin etc.

Macrolides                    e.g. Erythromycin, Lincomycin, Spiramycin, Gosamycin, Tylosin

Nitrofurans                    e.g. Nitrofurantoin etc.                   

Penicillin                       e.g. Ampicillin, Penicillin G, Amoxicillin, Cloxacillin, Nafcillin.

Polypeptide                  e.g. Bacitracin, Polymyxin B, Colistin.

Quinolones                   e.g. Nalidixic Acid, Ciprofloxacin, Enrofloxacin, Norfloxacin   Sulphonamides                  e.g. Sulpha Group Medicines

Tetracyclines                 e.g. Tetracycline, Oxytetracycline, Doxycyline, Chlortetracycline.

Antibiotics may destroy bacteria either by killing them (bactericidal action) or inhibiting their growth & multiplication (bacteriostatic action). Various classes of antibiotics have the bacteria destroying action as shown below:

Class of Antibiotic                                            Action

Aminoglucosides                                              Bactericidal

Cephalosporins                                                 Bactericidal

Glycopeptides                                                  Bactericidal

Nitrofurans                                                        Bactericidal

Polypeptides                                                    Bactericidal;

Penicillins                                                         Bactericidal

Quinolones                                                       Bactericidal

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Chloramphenicol                                               Bacteriostatic

Macrolides                                                        Bacteriostatic

Sulphonamides                                                 Bacteriostatic

Tetracycline                                                       Bacteriostatic

The above two actions may overlap & bacteriostatic antibiotics may become bactericidal in very high concentration.

The simultaneous use of two or three antibiotics is to be done in specifically defined situations. An appropriate combination requires an understanding of the potential of interaction between the antibiotics. Such interactions may affect both the micro-organisms & the host. Since various classes of antibiotics exert different action on micro-organisms, one drug may have the potential of either to enhance or inhibit the effect of the other.

A general description of synergism and antagonism is given below:

Synergism       : Their combined effect is greater than the individual effect of any one of them.

Example           : Bactericidal antibiotic with another bactericidal may be synergistic.                       

Antagonism     : Their combined effect is less than their individual effects.

Example           : Bactericidal with bacteriostatic may be antagonistic.

Dosage Regimen of Some Antimicrobial Agents In Ruminants

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I.V=Intravenous, I.M=Intramuscular, P.O=Per Os (orally 

                                                                                                                   Antibacterial action and Spectrum of different Antimicrobial Agents