Ppt is related to the introduction to antibiotics, contain the classification, mechanism of action along with sar and structure. Major category was included in the general classification of the antibiotics.

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Faculty of Pharmacy
Antibiotics 1
Lecture No.3

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Faculty of Pharmacy
Contents
• History & Introduction
• Commercial Production of antibiotics
• Over view of Mechanism of action of various antibiotics
• Various methods of Classification of Antibiotics

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Faculty of Pharmacy
At the end of this lecture, student will be able to
• Understand the history of evolution of antibiotics as therapeutic
agents
• Define the term “antibiotic”
• Explain how antibiotics are commercially produced
• Explain the general mode of action of various antibiotics
• Classify antibiotics based on various criteria
Learning Objectives

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Faculty of Pharmacy
History:
Modern Antibiotic era
• Initiated by the accidental discovery of the anti-bacterial properties
of Penicillin in 1929 by Sir Alexander Fleming
• Florey and Chain introduced Penicillin into therapy [1938]
• Definition (original) [By WAKSMAN (1942)]
• “ An antibiotic or antibiotic substance is a substance produced by
micro-organisms, which has the capacity of inhibiting the growth
and even of destroying other micro-organisms”

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Faculty of Pharmacy
Introduction Contd…
Modern Definition:
• “ Any substance produced by a living organism that is capable of
inhibiting the growth or survival of one or more species of micro-
organisms in low concentrations”
• Modified by Medicinal Chemists to include the substances obtained
from natural, semi-synthetic and synthetic sources

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Faculty of Pharmacy
Introduction Contd…
Hence a substance is classified as an antibiotic if the following
conditions are met:
• It is a product of metabolism
• It is a synthetic product produced as a structural analogue of a
naturally occurring antibiotic
• It antagonizes the growth or survival of one or more species of
micro-organisms
• It is effective in low-concentrations

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COMMERCIAL PRODUCTION: (of antibiotics)
The general scheme of commercial production of antibiotics for
medicinal use may be divided into six steps:
• Preparation of a pure culture of the desired organism for
inoculation of the fermentation medium.
• Fermentation, during which the antibiotic is formed.
• Isolation of the antibiotic from the medium
• Purification
• Assays for potency, sterility, absence of pyrogens and other
necessary data
• Formulation into acceptable and stable dosage forms.

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MECHANISM OF ACTION
• Mechanisms of action of some common antibiotics are as follows:-
Site of action Antibiotic Process interrupted Type of activity
1 Cell wall Penicillins
Cephalosprins
Cycloserine
Vancomycin
Bacitracin
Cell-wall cross linking
Cell-wall cross linking
Synthesis of Cell wall peptides
Muco-peptide synthesis
Muco-peptide synthesis
Bactericidal
Bactericidal
Bactericidal
Bactericidal
Bactericidal
2 Cell membrane Amphotericin B
Nystatin
Polymyxins
Membrane function
Membrane function
Membrane Integrity
Fungicidal
Fungicidal
Bactericidal
3 Ribosomes Chloramphenicol Protein synthesis Bactericidal
50 S subunit Erythromycin
Lincomycins
Protein synthesis
Protein synthesis
Bactericidal
Bactericidal
30 S subunit Aminoglycosides
Tetracyclines
Protein synthesis & fidelity
Protein synthesis
Bactericidal
Bacteriostatic
4 Nucleic Acids Actinomycin
Griseofulvin
DNA & mRNA synthesis
Cell division, microtubule Assembly
Pancidal
Fungicidal
DNA and /or RNA Mitomycin
Rifampin
DNA synthesis
mRNA synthesis
Pancidal
Bactericidal

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MECHANISM OF ACTION Contd…
“ ANTIBIOTICS THAT INTERFERE WITH THE METABOLIC SYSTEMS
FOUND IN MICRO-ORGANISMS AND NOT IN MAMALIAN CELLS ARE
THE MOST SUCCESSFUL ANTI-INFECTIVE AGENTS”
For example,
• Antibiotics that interfere with the synthesis of bacterial cell walls
have a high potential for selective toxicity.
 Cycloserine is an antimetabolite of D-Alanine, a constituent of
bacterial cell wall.

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Faculty of Pharmacy
MECHANISM OF ACTION Contd…
 Many antibiotics like aminoglycosides, tetracyclines etc selectively
interfere with microbial protein synthesis or nucleic acid synthesis like
Rifampin.
 Others like polymixins and polyenes, interfere with the integrity and
function of microbial cell membranes.
• The agents may be a bactericidal or a bacteriostatic.
• This distinction is important for the treatment of serious, life-
threatening infections, particularly if the natural defense mechanisms
of the host are either deficient or overwhelmed by the infection – in
such cases, a bactericidal is indicated.

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CLASSIFICATION (of Antibiotics)
• Various criteria are used to classify ‘ Antibiotics’
 I method:
Based on the clinical effectiveness, spectrum of activity and degree of
selectivity.
Class 1:- Those inhibiting only one group of micro-organisms
• “Narrow Spectrum Antibiotics” eg. Nystatin and Bacitracin.
• Exhibit a high degree of selectivity.
Class 2:- Those inhibit both “Gram +Ve” and “Gram -Ve” bacterial and
/or other intracellular organisms.
• “ Broad Spectrum Antibiotics” eg. Chloramphenicol and Tetracyclin.

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CLASSIFICATION (of Antibiotics) contd…
 II method: based on the sources from which antibiotics are
obtained. They can be classified as
a. Natural:- obtained from the large scale fermentation of micro-
organisms.
Eg. ‘ Bacitracin’ and ‘Polymixin’ are obtained from some bacilli.
‘Streptomycin’ and ‘Tetracycline’ are obtained from streptomyces
species
b. Semi-synthetic:- The precursors of these antibiotics are obtained
from natural source. Synthetic method is utilized to produce the
analogues/derivatives of these precursors.

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CLASSIFICATION (of Antibiotics) contd…
For example: 6-Aminopenicillanic acid is obtained from the cultures of
P. Chrysogenum. During the commercial production of benzyl penicillin
(Penicillin G), Phenyl acetic acid is added to the medium in order to
get the product.
c. Synthetic:- This class includes antibiotics which are having purely
synthetic origin.
• For example: Chloramphenicol (a broad spectrum antibiotic),
ciprofloxacin,etc

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CLASSIFICATION (of Antibiotics) contd…
 III method: based on the differences in the mechanism of action.
A. Drugs that interferes with the biosynthesis of bacterial cell-wall
Eg. Penicillins, Cephalosprins, Cycloserin, Bacitracin & Vancomycin.
B. Drugs that interfere in the functioning of Cytoplasmic membrane.
Eg. Polymixins, Aphotericin B and Nystatin.
C. Drugs that interfere with the protein biosynthesis.
Eg. Erythromycin, Lincomycins, Tetracyclines and Chloramphenicol.
D. Drugs that interfere with Nucleic acid biosynthesis
Eg. Actinomycin, Griseofulvin and Rifampin.

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CLASSIFICATION (of Antibiotics) contd…
 IV method: based on the chemical structure.
 Β-lactam Antibiotics:
Eg. Penicillins, Cephalosprins, Monobactams.
 Aminoglycosides:
Eg. Kanamycin, Streptomycin, Gentamycin, Neomycin, etc.
 Tetracycline Antibiotics:
Eg. Tetracycline, Chlortetracycline, Oxytetracycline, etc.

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Faculty of Pharmacy
CLASSIFICATION (of Antibiotics) contd…
 Peptide Antibiotics:
Eg. Amphomycin, Tyrothricin, Bacitracin, etc.
 Macrolide Antibiotics:
Eg. Erythromycin, Oleandomycin
 Lincomycin:
Eg. Lincomycin, Clindamycin, pirlimycin
 Unclassified Antibiotics:
Eg. Chloramphenicol, Rifamycin.
 “Anti-fungal Antibiotics”
Eg. Griseofulvin, Polyene Antibiotics (Amphotericin B, Nystatin,
Candicidin)

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Faculty of Pharmacy
Summary
• Penicillin was discovered and introduced into therapy by Sir.
Alexander Fleming & Florey and Chain respectively
• Definition of Antibiotic
• Steps involved in commercial production of antibiotics
• Mechanism of action - overview
• Four methods of classification