1. Antimicrobial drugs can be classified into five main categories based on their mechanism of action, source, spectrum of activity, chemical structure, and function. 2. Examples of classes of antimicrobial agents include beta-lactam drugs, protein inhibitors such as tetracyclines and aminoglycosides, DNA synthesis inhibitors like fluoroquinolones. 3. Antimicrobial drugs are used to treat microbial infections and include antibiotics, antifungals, antiprotozoals, and antivirals such as acyclovir and idoxuridine.

1. Dr. Jibachha Sah
M.V.Sc(Veterinary Pharmacology)
Lecturer, College of veterinary science, NPI, Bhojard, Chitwan, Nepal
jibachhashah@gmail.com
Classification; General principles in
antibacterial chemotherapy
SEVENTH SEMESTER !
Veterinary Pharmacology & Toxicology(Chemotherapy)
Lecturer-Second

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1.Definition
2.Classification
2.1 Classification based on type of mechanism of action
2.2 Classification based on source of antibacterial agents
2.3 Classification based on spectrum of activity
2.4 Classification based on chemical structure
2.5 Function‐based classification of antibacterial drugs
3.Summary

3. INTRODUCTION
Bacteria are simple one‐celled organism,
which were first identified in the 1670s by
van Leeuwenhoek.
These efforts led to the revolutionary
discovery of the antibacterial agent
“penicillin” in 1928 from Penicillium notatum
by Sir Alexander Fleming.
The Modern era of chemotherapy was ushered by
Domagk in 1935 by demonstrating the therapeutic
effect of Prontosil, a sulfonamide dye, in pyogenic
infection. It was soon realized that the active
moiety was paraamino benzene sulfonamide, and
the dye part was not essential.

4. CLASSIFICATION
M a i n l y c l a s s i f y
i n f i v e g r o u p
The antibacterial agents can
be classified into five major groups, i.e.
1.Based on the mechanism of action
2.Classification based on the source
3.Based on spectrum of activity
4.Based on chemical structure
5. Function‐based classification of antibacterial
drugs

5. 1 . C l a s s i f i c a t i o n b a s e d
o n m e c h a n i s m o f
a c t i o n
Generally, antibacterials can be classified on
the basis of type of action: bacteriostatic and
bactericidal.
Antibacterials, which destroy bacteria by
targeting the cell wall or cell membrane
of the bacteria, are termed bactericidal
and
those that slow or inhibit the growth of bacteria
are referred to as bacteriostatic.
●Inhibit cell wall synthesis – penicillin,
cephalosporin, cyclosesrine, vancomycin,
bacitracin
● Cause leakage from cell membrane:
polypeptides and polyenes
● Inhibit protein synthesis: tetracyclines
chloramphenicol,erythromycin,clindamycin

6. ● Cause misreading of mRNA code and affect permeability : aminoglycosides
● Interfere with DNA function : rifampin, metronidazole
● Interfere with DNA synthesis: idoxuridine,acyclovir,zidovudine
● Interfere with intermediary metabolism: sulfonamides,sulfones,pas, trimethoprim
● Inhibit DNA gyrase : fluroquinolones.

7. Trimethoprim binds to
dihydrofolate reductase
and inhibits the
reduction of dihydrofolic
acid (DHF) to
tetrahydrofolic acid
(THF). THF is an
essential precursor in
the thymidine synthesis
pathway and
interference with this
pathway inhibits
bacterial DNA synthesis.

8. 2.Classification based
on the source
Sources of Antibiotics
●Natural : mainly fungal sources
(e.g Benzylpenicillin and
Gentamycin)
● Semi synthetic: chemically
altered natural compound (e.g
Ampicillin & Amikacin).
● Synthetic: chemically designed
in the lab (e.g Moxifloxacin and
Norfloxacin).
●Fungi - penicillin, cephalosporins
and griseofulvin
● Bacteria - polymyxinb, colistin and
bacitracin
● Actinomycetes - aminoglycosides,
tetracycines, chloramphenicol,
macrolides and polyenes

11. 3.Classification
based spectrum of
activity
● Narrow spectrum: (activity against
either gram positive or gram negative
organism) - eg: penicillin and
streptomycin
● Broad spectrum: (both gram positive
or gram negative) - eg: tetracyclines,
chloramphenicol and erythromycin
● But now extended spectrum
penicillins, newer cephalosporins,
fluroquinolones are now available. Some
agents capable of acting on bacteria,
rickettsia and protozoa also.

12. 4.Classification
based chemical
nature
● Sulfonamides and related drugs :
sulfadiazine, paraaminosalicylic acid
● Diaminopyrimidines:
trimethoprim,pyrimehamine
● Quinolones and fluroquinolones :
nalidixic acid, norfloxacin, ciprofloxacin
erc
● Beta lactum antibiotics : penicillin,
cephalosporins,monobactams,carbapen
ems

13. ●Tetracycines, oxytetracyclines,doxycylines etc
● Nitrobenzene derivate: chloarmphenicol
● Aminoglycosides : streptomycin, gentamicin, neomycin etc
● Macrolide antibiotics; ertyromycin, roxithromycin,azithromycin
● Polypeptide antibiotics: polymyxin-B, colistin, bacitracin
● Glycopeptides; vancomycin.teicoplanin
● Nitrofuran derivatives : nitrofurantoin,fruazolidone

14. ● Nitroimidazoles: metronidazole, tinidazole
● Nicotinic acid derivatives; isoniazid, pyrizinamide
● Polyene antibiotics: nystatin, amphotericin-b
● Azole derivatives; miconozole,ketokonazole.fluconazole
● Others : rifambin. Lincomycin spectinomycin, griseofulvin etc

15. ion
5.Function‐based
classification of
antibacterial drugs
● Antibacterials : penicillins, aminoglycosides,
erythromycin etc
● Antifungal : griseofulvin.amphotericin -B ketoconazole
● Antiviral : idoxuridine,acyclovir
● Antiprotozoal ; fluroquinine,pyrimethamine,metrnidaole
● Anthelmintic ; mebendazole, pyrantal dec etc.
● Antituberculosis : isoniazid, rifampin, ethambutol

16. Summary
1.What are the five main classes of antimicrobial drugs?
(i)type of action,
(ii) source,
(iii)spectrum of activity,
(iv)chemical structure, and
(v) function.
2.What are the classes of antimicrobial agents?
Antimicrobial agents are classified into several categories, i.e. inhibitors for bacterial cell wall such as beta-
lactam drugs, fosfomycin, and vancomycin; inhibitors for protein biosynthesis such as tetracycline, macrolides,
aminoglycoside antibiotics; inhibitors for DNA synthesis such as 4-quinolones; inhibitors .

17. 3.What is an example of an antimicrobial drug?
Antimicrobial Drugs are drug used to treat a microbial infection. Examples antibiotics, antifungals, antiprotozoal,
and antiviral drugs.
4. What are the 5 classes of antibiotics?
(i)Beta-Lactams.
(ii)Macrolides.
(iii)Fluoroquinolones.
(iv)Tetracyclines.
(v)Aminoglycosides.
5.What is the difference between a bactericidal and bacteriostatic agent?
The definitions of “bacteriostatic” and “bactericidal” appear to be straightforward: “bacteriostatic” means that
the agent prevents the growth of bacteria (i.e., it keeps them in the stationary phase of growth), and “bactericidal”
means that it kills bacteria.

18. 6.What is natural source antimicrobial drug?
(i) e.g Benzylpenicillin and Gentamycin)
7.What is semisynthetic source of antimicrobial drug?
(i)e.g Ampicillin & Amikacin
8. What is synthetic source of antimicrobial drug?
(i) e.g Moxifloxacin and Norfloxacin
9. Idoxuridine, acyclovir are which class of drugs?
(i) Antiviral
10. Isoniazid, rifampin, ethambutol are which class of drugs?
(i) Antituberculosis

19. 11. What is mechanism of action of tetracycline's, chloramphenicol,
erythromycin and clindamycin?
(i) Inhibit protein synthesis
12. What is mechanism of action of rifampin and metronidazole ?
(i) Interfere with DNA function
13. What is mechanism of action of fluroquinolones?
(i) Inhibit DNA gyrase
14. What are the 3 examples of aminoglycosides drug?
(i) streptomycin, gentamicin, neomycin

20. 15. What are the 3 examples of Macrolide antibiotics?
(i)Ertyromycin, roxithromycin and azithromycin
16. Isoniazid and pyrazinamide are what types of antibiotic?
(i) Nicotinic acid derivatives
17. Polymyxin-B, colistin and bacitracin are what types of antibiotics?
(i) Polypeptide antibiotics