Antibiotics are chemical substances produced by microorganisms that can kill or inhibit the growth of other microorganisms at low concentrations. They are classified based on their mechanism of action and chemical structure. Major classes include beta-lactam antibiotics (penicillins, cephalosporins), aminoglycosides, tetracyclines, macrolides, and chloramphenicol. They work by inhibiting bacterial cell wall, membrane, or protein synthesis. Common side effects include diarrhea, rashes, and potential toxicity to kidney or liver.

1. Antibiotics
Presented By
Mr. Surya Nath Pandey
(Asst. Prof.)

2. ANTIBIOTICS
The term antibiotics has its origin in the world antibiosis that is a process in which
one organism may destroy another to preserve itself.
We should know thi very clear “Antibiosis” means against the life.
These are the chemical substances which is derived from different species of
microorganisms (bacteria, fungi, etc.) that suppress the growth of other
microorganisms and eventually may destroy them at low concentration.
However, all chemical substances produced by living cells cannot function as
antibiotics. In order to act as antibiotics, the compound must satisfy the following
conditions:-
It should be effective at low concentration against pathogens’
It should be product of metabolism analogue of naturally occurring antibiotics.
It should be stable and should be completely eliminated from syste.

3. CLASSIFICATION
They are classified as on the basis of mechanism of action and on the basis of chemical
structure:-
On the basis of mechanism of action:-
1. agents that inhibits the synthesis of bacterial cell walls:- penicillins, cephalosporins,
vancomycin, cycloserine, bacitracin, imidazole & antifungals.
2. agents that act directly on the cell membrane of microorganisms, affecting permeability
and leading to leakage of intracellular compounds:- polymyxin, polyene, nystatin,
amphotericin B.
3.agents that affects the function of 30s and 50s ribosomal subunits :- tetracycline,
erythromycin, chloramphenicol and clindamycin.
4.agents that binds to 30s ribosomal subunits and alters the protein synthesis: -
aminoglycosides
5. agents that affects the nucleic acid metabolism:- rifampicin.

4. On the basis of chemical structure :- 1. β-lactam antibiotics
2. Aminoglycosides 3. Tetracycline 4. Polypeptide antibiotics
5. Macrolides 6. Linomycins
1. Beta lactam antibiotics: - these are the antibiotics which have β-lactam
ring in their structure. It includes penicillins, cephalosporins,
monobactams and carbapenems. They are described as follows:-
Penicillins:- it was the discovered by Alexander Fleming in 1928. it was the
1st antibiotic used clinically in 1941. it is a miracle that the least toxic drug
of its kind was 1st to be discovered. It was originally obtained from
Penicillium notatum but present source is a high yielding mutant of
penicillium chrysogenum. It contains thiazolidine and β-lactam ring.

5. Classification
1. Penicillinase-susceptible penicillins: - penicillin G, penicillin V, penicillin O,
phonethicillin.
2. Penicillinase-resistant penicillins:- methicillin, cloxacillin, dicloxacillin.
3. Extend spectrum penicillins:- [A]. Aminopencillins:- ampicillin,
bacampicillin, amoxicillin.
[B].Carboxypenicillins: - carbapenicillin.
[C].Ureidopenicillins: - piperacillin, mezlocillin.
4. β-lactamase inhibitor:- clavulanic acid, sulbactam, tazobactam, avibactam,
relebactam.
This is the classification of penicillins now comes to the mechanism/mode of
action of penicillins. It is very easy to remember with the help of flow chart. All
penicillins have similar MOA but t1/2 is different. Lets see the MOA of
Penicillins:-

6. Mechanism of actions
Things to remember: - all antibiotics inhibits the protein synthesis,
DNA,RNA.
After that the inhibition of that things the bacteria, microorganisms
can not make their synthesis due to this inhibition.

7. MOA of Penicillins
Penicillins
Inhibits the synthesis of peptidoglycan layer containing NAG(N-acetyl glucosamine) and
NAM (N-acetyl muramic acid) connected by PBP(penicillin binding protein)
Acts on penicillin binding protein (PBP)
Cell wall synthesis inhibition
Bacteriostatic & bacteriocidal

8. Uses & adverse effects:-
Uses:- streptococcal infections, pneumococcal infection, gonorrhoea, syphilis,
tetnus, diphtheria, respiratory tract infection, urinary tract infection, etc.
Adverse effect:- kidney failure, neurotoxicity, diarrhea, GIT disturbance, chills,
fever, etc.

9. Cephalosporins
These are the semisynthetic antibiotic which is derived from cephalosporin-C
which is obtained from cephalosporium (fungus). The nucleus of its also have the
β-lactam ring fused to dihydro-thiazine ring.
Classification:- cephalosporins are categorized into four generations. They are
described as follows:-
1. 1st generation: - cefazolin, cephalothin, cephaloridine, cephapirin, cefadroxil,
cephalexin.
2. 2nd generation: - cefuroxime, cefoxitin, cefaclor, cefonicid, cefamandole.
3. 3rd generation: -ceftizoxime, cefotaxime, cefixime, ceftibuten, cefoperazone,
ceftazidime, cefdinir
4. 4th generation: - cefepime, cefpirome.
These are the classifications now comes to the mechanism of action. MOA of all
drugs are similar but they have different t1/2.

10. Mechanism of action
Cephalosporins
Binds to CBP (cephalosporin binding protein) or PBP-1 or PBP-3
Inhibits the synthesis of peptidoglycan layer
Inhibition of cell wall synthesis

11. β-lactamase inhibitors
These are a family of enzymes involved in bacterial resistance to β-lactam
antibiotics. They act by breaking the β-lactam ring that allows penicillin like
antibiotics to work. They includes clavulanic acid, sulbactam, tazobactam,
avibactam, relebactam.
MOA of clavulanic acid: -

12. Clavulanic acid
Binds with serine (amino acids makes proteins) residue in β-lactamase
Creates a highly active complex this complex binds with amino acids of β-
lactamase
Permanently inactive β-lactamse enzyme
Complete protection against resistant pathogens

13. Aminoglycoside
It is a molecule composed of amino modified sugars. It has a hexose ring, either
streptidine and various amino sugars are attached to this ring by glycosidic
linkage. Streptomycin was the 1st antibiotic of this group . It was discovered by
Waksman and his collegue in 1944, isolated from a strain of Streptomyces griseus.
Waksman got the nobel prize in 1952. Neomycin was dicovered in 1949 and
kanamycin was discovered in 1960. All aminoglycosides are produced by soil
actinomycetes.
Classification: -
a) Systemic:- streptomycin, gentamycin, amikacin, kanamycin, tobramycin,
sisomicin, netilmicin.
b) Topical: - neomycin, framycetin.
Now comes to the mechanism of action. All aminoglycosides have similar MOA but
they have different t1/2.

14. MOA
Aminoglycosides
Binds with 30s ribosomal unit
Inhibits the initiation of protein synthesis
Cause misreading of genetic code on recognition region of ribosome
Insertion of wrong amino acids
Destruction of cell membrane

15. Tetracycline
These are class of antibiotics having a nucleus of four cyclic rings. All are obtained
from soil actinimycetes. Chlortetracycline was the 1st drug which introduced in
1948. all tetracyclines are slightly bitter solids which are slightly soluble in water,
but their hydrochlorides are more soluble. All TCs have the same antimicrobial
activity practically.
Classifications: -
1.Natural tetracyclines: - tetracycline, chlortetracycline, oxytetracycline,
bromotetracycline, dexamethyltetracycline.
2. Semisynthetic tetracyclines: - doxycycline, minocycline, methacycline,
sancycline.
3. Protetracycline: - rolitetracycline, lymecycine, apicycline, meglucycline.
Now comes to the MOA, every drug have the similar MOA but they have
different t1/2.

16. MOA
Tetracyclines
Binds to A(aminoacyl t-RNA) site of 30s ribosomal subunit
Prevent binding of t-RNA to A site
Chain fails to grow
Prevent protein synthesis

17. Macrolides
These are antibiotics having a macrocyclic lactone ring with attached sugars.
Erythromycin was the 1st member discovered in 1950s. Roxithromycin,
clarithromycin and azithromycin, later added.
Now comes to the mechanism of action which are described as follows:-

18. MOA
Macrolides
Binds to 50s ribosomal unit
Inhibits polypeptide chain elongation & protein synthesis inhibition
Results in inhibition of growth and multiplication
Erythromycin (MOA): - binds to 23s rRNA molecule in 50s.
Uses: - respiratory tract infection, urinary tract infection, H. pylori, pneumonia.
Adverse effect:- kidney failure, GI problems, neurotoxicity.

19. Chloramphenicol
It was initially obtained from Streptomyces venezuelae in 1947. it was soon
synthesized chemically and commercial product now it is all synthetic. It is a
yellowish white crystalline solid, aqueous solution is quite stable. The
nitrobenzene moiety of this is probably responsible for antibacterial activity as
well as its bitter taste.
MOA

20. MOA
Chloramphenicol
Attaches to 50s ribosomes
Near acceptor (A) site for amino acids incorporation by acting as a
peptide analogue
Prevents peptide bonds
Inhibition of protein synthesis at peptidyl transferase reaction

21. Uses: - anaerobic infections, intraocular infections, urinary tract
infections.
Adverse effects: - bone marrow depression, anemia, thrombocytopenia.
This is all about antibiotics. Categorywise drugs are well described in these
slides. Most of the drugs are described in these slides.