As per the syllabus prescribed by PCI for diploma in Pharmacy.

1. ANTIBIOTICS
-Ambareen Fatima Ahmed
Lecturer,
School of Pharmaceutical sciences,
Integral University, Lucknow.

2. Definition
These are substances produced by microorganisms, which selectively
suppress the growth of or kill other microorganisms at very low
concentrations.
A substance is classified as an antibiotic if the following conditions are met:
1. It is a product of metabolism (although it may be duplicated or even have
been anticipated by chemical synthesis).
2. It is a synthetic product produced as a structural analog of a naturally
occurring antibiotic.
3. It antagonizes the growth or survival of one or more species of
microorganisms.
4. It is effective in low concentrations.
Antibiotics are used to treat life-threatening bacterial diseases and other
infections caused by protozoa and fungi.

3. CLASSIFICATION
A) Chemical structure
 β-Lactam antibiotics: Penicillins,
Cephalosporins, Monobactams, Carbapenems.
 Tetracyclines: Oxytetracycline, Doxycycline.
 Nitrobenzene derivative: Chloramphenicol.
 Aminoglycosides: Streptomycin,
Gentamicin, Amikacin, Neomycin.
 Macrolide antibiotics: Erythromycin, Clarithromycin,
Azithromycin.
 Lincosamide antibiotics: Lincomycin, Clindamycin.
 Glycopeptide antibiotics: Vancomycin, Teicoplanin.
 Polypeptide antibiotics: Polymyxin-B, Colistin,
Bacitracin, Tyrothricin.
 Polyene antibiotics: Nystatin, Amphotericin- B,
Hamycin.
B) Depending upon source
 Fungi
Penicillin
Griseofulvin
Cephalosporin
 Bacteria
Polymyxin B
Colistin
Aztreonam
Bacitracin
 Actinomycetes
Aminoglycosides
Macrolides
Tetracyclines
Polyenes
Chloramphenicol

4. C. 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,
Clindamycin.
4. Cause misreading of m-RNA code
and affect permeability:
Aminoglycosides— Streptomycin,
Gentamicin.
5. Interfere with DNA function: Rifampicin.

5. These are antibiotics having a β-lactam ring. The two major groups are
penicillins and cephalosporins.
Penicillins – Amoxycillin, Cloxacillin, Penicillin V
Cephalosporins – Cephalexin, Cefuroxime
A) Penicillins
The penicillin nucleus consists of fused thiazolidine and β-lactam rings to
which side chains are attached through
an amide linkage.
MOA: All β-lactam antibiotics interfere with the
synthesis of bacterial cell wall.
The β-lactam antibiotics inhibit the
Transpeptidases so that cross linking (which maintains the close
knit structure of the cell wall) does not take place.
Beta-Lactam Antibiotics

6. NAMING
BRIDGED
BICYCLIC
COMPOUNDS

7. IUPAC name: 3,3-dimethyl-7-oxo-6-[(2-phenylacetyl)amino]-4-thia-
1-azabicyclo[3.2.0]heptane-2-carboxylic acid
PP: Available as Na+ and K+ Salts.
i) Amorphous white powder ii) Odourless iii) Hygroscopic
iv) Sparingly soluble in water. v) Soluble in methanol.
Stability:
In the dry state, natural penicillins and their salts are generally stable for several yr @ room temp.
PnG is also thermolabile and acid labile.
Commercially available salt powders for injection may be stored @ room temp. Following reconstitution of the
powders for injection, salt solutions are stable for 7 days @ 2-8 °C. Soln of the drugs prepared for IV administration
are generally stable for 24 hr @ room temp. Solutions are freshly prepared.
Storage: Stored at room temperature, protected from light and heat.
Use: Antibacterial - Streptococcal infections, Pneumococcal infections, Meningococcal infections, Syphilis. They are
used in the treatment of Infections of the middle ear, Upper Respiratory tract infections (tonsils, throat, larynx
(laryngitis), Lung infections (bronchitis, pneumonia), Urinary tract infections, Gonorrhea, Skin infections.
Brand: 1) Sodium salt -- BENZYL PENICILLIN 0.5, 1 MU inj.
Penicillin (penicillin G or benzylpenicillin)

8. Benzathine penicillin
 Benzathine penicillin is a salt of PnG prepared by combining the sodium salt of
penicillin G with N,N'-dibenzylethylenediamine.
 Benzathine penicillin G 0.6–2.4 MU i.m. every 2–4 weeks as aqueous
suspension.
 It releases penicillin extremely slowly—plasma concentrations are very low but
remain effective for prophylactic purposes for up to 4 weeks.
Brands: PENIDURE-LA (long acting), LONGACILLIN, PENCOM, 0.6, 1.2, 2.4
MU as dry powder in vial.

9. SEMISYNTHETIC PENICILLINS
• Semisynthetic penicillins are produced by chemically combining specific side chains (in place of benzyl
side chain of PnG).
• The aim of producing semisynthetic penicillins has been to overcome the shortcomings of PnG, which
are:
1. Poor oral efficacy.
2. Susceptibility to penicillinase.
3. Narrow spectrum of activity.
4. Hypersensitivity reactions (this has not been overcome in any preparation).
CLASSIFICATION
1. Acid-resistant alternative to penicillin G
E.g.: Phenoxymethyl penicillin (Penicillin V).
2. Penicillinase-resistant penicillins
E.g.: Methicillin, Cloxacillin, Dicloxacillin.
3. Extended spectrum penicillins
(a) Aminopenicillins: Ampicillin, Bacampicillin, Amoxicillin.
(b) Carboxypenicillins: Carbenicillin.
(c) Ureidopenicillins: Piperacillin, Mezlocillin.
• β-lactamase inhibitors Clavulanic acid, Sulbactam, Tazobactam

10. Phenoxy methyl penicillin (Penicillin V)
 It is a semisynthetic penicillin.
 Acid-resistant alternative to penicillin G.
It differs from PnG only in that it is acid stable.
IUPAC name: 3,3-dimethyl-7-oxo-6-[(2-phenoxyacetyl)amino]-4-thia-1-
azabicyclo[3.2.0]heptane-2-carboxylic acid
Brands:
CRYSTAPEN-V, KAYPEN 125, 250 mg tab, 125 mg/5 ml dry syr—for
reconstitution, PENIVORAL 65, 130 mg tab.

11. Cloxacillin
 It is highly penicillinase as well as acid resistant.
• PP: i) WHITE, CRYSTALLINE POWDER. ii) ODORLESS
iii) BITTER TASTE iv) SOLUBLE IN ALCOHOL v) Aq. SOLn IS
ALKALINE.
• Stability:
CLOXACILLIN IS RELATIVELY STABLE IN GASTRIC ACID;
STABLE IN LIGHT; SLIGHTLY HYGROSCOPIC.
AQ. SOLN FOR INJECTIONS ARE STABLE FOR AT LEAST 3
DAYS IF REFRIGERATED.
 Stable in the dry state @ room temp for several yr; however, the drugs
are stable only for short periods of time in soln unless frozen. Stability of
the drugs is pH and temp dependent.
• Brands: KLOX, BIOCLOX, 0.25, 0.5 g cap; 0.25, 0.5 g/vial inj.,
CLOPEN 0.25, 0.5 g cap.

12. Ampicillin
Ampicillin is a broad-
spectrum, semi-synthetic,
beta lactam penicillin antibioti
c with bactericidal activity.
PP:
i) White, crystalline powder
ii) odorless iii) bitter taste
Stability: Aminopenicillins are
generally stable in the dry
state; however, the drugs are
stable only for short periods
time in soln. Like other
penicillins, the stability of
aminopenicillins is pH and
temp dependent.
IUPAC name: 6-[[-2-amino-2-
phenylacetyl]amino]-3,3-dimethyl-7-oxo-4-thia-
1-azabicyclo[3.2.0]heptane-2-carboxylic acid.
Brands: AMPILIN, ROSCILLIN, BIOCILIN 250, 500
mg cap; 125, 250 mg/5 ml dry syr; 100 mg/ml pediatric
drops; 250, 500 mg and 1.0 g per vial inj.

13. Carbenicillin
Carbenicillin is inactive orally.
The special feature of this penicillin congener is its activity against
Pseudomonas aeruginosa and indole positive Proteus which are not inhibited by
PnG or aminopenicillins.
Carbenicillin is a broad-spectrum, semi-synthetic penicillin antibiotic with bactericidal
and beta-lactamase resistant activity.
PP: i) WHITE TO OFF-WHITE, CRYSTALLINE POWDER ii) BITTER TASTE iii)
HYGROSCOPIC iv) ODORLESS
Stability: Extended-spectrum penicillin's are generally stable for several year in the dry
state @ room temp; however, the drugs are stable only for short periods of time in
solution unless frozen.
Brands: CARBELIN 1 g, 5 g, per vial inj.

14. B) Cephalosporins
These are a group of semisynthetic antibiotics derived from
‘cephalosporin-C’ obtained from a fungus Cephalosporium.
They are chemically related to penicillins; the nucleus consists
of a β-lactam ring fused to a di-hydrothiazine ring, (7-
aminocephalosporanic acid).
By addition of different side chains at position 7 of β-
lactam ring (altering spectrum of activity) and at position 3
of di-hydrothiazine ring (affecting pharmacokinetics), a large
number of semisynthetic compounds have been produced.
These have been conventionally divided into 4 generations.
This division has a chronological sequence of development,
but more importantly, takes into consideration.
All cephalosporins are bactericidal and have the same
mechanism of action as penicillin, i.e. inhibition of bacterial
cell wall synthesis.

15. CLASSIFICATION
Individual cephalosporins differ in their:
(a) Antibacterial spectrum and relative potency against specific
organisms.
(b) Susceptibility to β-lactamases elaborated by different organisms.
(c) Pharmacokinetic properties.
FIRST GENERATION CEPHALOSPORINS
Developed in the 1960s, have high activity against gram-positive but
weaker against gram-negative bacteria.
SECOND GENERATION CEPHALOSPORINS
Developed subsequent to the first generation compounds and are more
active against gram-negative organisms.
THIRD GENERATION CEPHALOSPORINS
These compounds introduced in the 1980s.
FOURTH GENERATION CEPHALOSPORINS
Non-susceptibility to β lactamases, high potency against
Enterobacteriaceae and spectrum of activity similar to 3rd generation
compounds.

16. Uses
Currently cephalosporins are one of the most commonly used
antibiotics.
Antibacterial.
As alternatives to penicillins
for ENT, upper respiratory and cutaneous infections.
Respiratory, urinary and soft tissue infections.
Surgical prophylaxis.
Meningitis.
Typhoid.
Hospital acquired infections, especially respiratory and other infections
in intensive care units, resistant to commonly used antibiotics.

17. Cephalexin
• It is the most commonly used orally effective
first generation cephalosporin.
PP:
• i) white crystalline monohydrate. ii) It is
freely soluble in water. iii) Resistant to acid,
and absorbed well orally.
Stability: Acid stable.
Uses: Treatment of urinary tract infections.
It is also sometimes used for upper respiratory
tract infections.
Brands:
• CEPHACILLIN 250, 500 mg cap;
SPORIDEX, ALCEPHIN, CEPHAXIN 250,
500 mg cap, 125 mg/5 ml dry syr., 100
mg/ml pediatric drops.
Cephalothin
• Cephalothin is a semisynthetic, beta-lactam,
first-generation cephalosporin antibiotic.
PP:
i) white to off-white, crystalline powder ii)
practically odorless. iii) It is freely soluble in
water iv) insoluble in most organic solvents.
Stability: Acid stable.
• Solutions of cephalothin may darken,
especially if stored at room temperature. A
slight discoloration does not affect potency.
Solutions stored under refrigeration may
precipitate, but the precipitate can be re-
dissolved by warming to room temperature
with constant agitation.
Uses: Bactericidal activity.

18. Tetracyclines and Chloramphenicol
(Broad-Spectrum Antibiotics)
1) TETRACYCLINES
• These are a class of antibiotics having a nucleus of four cyclic rings.
• All tetracyclines are slightly bitter solids which are slightly water soluble, but their
hydrochlorides are more soluble.
• Aqueous solutions are unstable.
• All have practically the same antimicrobial activity (with minor differences).
• The tetracyclines still available in India for clinical use are:
Tetracycline Doxycycline
Oxytetracycline Minocycline
Demeclocycline
Tigecycline
Mechanism of action : The tetracyclines are primarily bacteriostatic; inhibit protein synthesis in
bacteria's.
Brands: Tetracycline: ACHROMYCIN, HOSTACYCLINE, RESTECLIN 250, 500 mg cap. 3%
skin oint, 1% eye/ear drops and oint.

19. CHLORAMPHENICOL
• Chloramphenicol was initially obtained from Streptomyces venezuelae in 1947.
• It was soon synthesized chemically and the commercial product now is all synthetic.
PP: i) It is a yellowish white crystalline solid. ii) Intensely bitter taste.
Stability: Aqueous solution is quite stable, stands boiling, but needs protection from light.
• The nitrobenzene moiety of chloramphenicol is probably responsible for the antibacterial
activity as well as its intensely bitter taste.
Mechanism of action: Chloramphenicol inhibits bacterial protein synthesis.
• It is bacteriostatic.
Uses: Clinical use of chloramphenicol for systemic infections is now highly restricted due to fear
of fatal toxicity.
Typhoid, Meningitis, UTI, Infection of eye and ear, Intracranial bacterial infection,
Brands: CHLOROMYCETIN, ENTEROMYCETIN, PARAXIN, 250 mg, 500 mg cap, 1% eye
oint, 0.5% eye drops, 5% ear drops.

20. Aminoglycosides Antibiotics
These are a group of natural and semisynthetic antibiotics having
polybasic amino groups linked glycosidically to two or more
aminosugar (streptidine, 2-deoxy streptamine, garosamine) residues.
Classification
Systemic aminoglycosides
Streptomycin Amikacin
Gentamicin Sisomicin
Kanamycin Netilmicin
Tobramycin Paromomycin
Topical aminoglycosides
Neomycin Framycetin

21. MECHANISM OF ACTION of AMINOGLYCOSIDES
• The aminoglycosides are bactericidal antibiotics, all having the same general pattern of
action which may be described in two main steps:
(a) Transport of the aminoglycoside through the bacterial cell wall and cytoplasmic membrane.
(b) Binding to ribosomes resulting in inhibition of protein synthesis.
Common properties of aminoglycoside antibiotics
1. All are used as sulfate salts, which are highly water soluble; solutions are stable for months.
2. They ionize in solution; are not absorbed orally.
3. All are excreted unchanged in urine by glomerular filtration.
4. All are bactericidal and more active at alkaline pH.
5. All are active primarily against aerobic gram-negative bacilli and do not inhibit anaerobes.
6. They have relatively narrow margin of safety.
7. All exhibit ototoxicity and nephrotoxicity.

22. • Gentamicin
• PP
• i) White amorphous
powder ii) Odorless iii) Freely
soluble in water iv) insoluble in
alcohol, acetone.
• Stability: Stable in light, air, and
heat /Gentamycin sulfate
• USES: Gentamicin for infections
that cause sepsis, pneumonia and
for eye infections
• BRANDS: GARAMYCIN,
GENTASPORIN, GENTICYN 20, 60,
80, 240 mg per vial inj; also 0.3%
eye/ear drops, 0.1% skin cream.
• Neomycin
 Available as sulphate salt.
 A broad spectrum aminoglycoside antibiotic.
• PP:
i) Neomycin is liquid in nature. Neomycin sulphate is amorphous
white powder. ii) Practically tasteless.
iii) Soluble in water and alcohol.
iv) Insoluble in most organic solvents.
• Stability and storage: Hygroscopic. /Neomycin sulfate
• USES: 1. Topically (often in combination with polymyxin,
bacitracin, etc.) for infected wound, ulcers, burn, external ear
infections, conjunctivitis, but like other topical anti-
infective preparations, benefits are limited.
2. Orally for: (a) Preparation of bowel before surgery.
• BRANDS: NEOMYCIN SULPHATE 350, 500 mg tab, 0.3%
skin oint, 0.5% skin cream, eye oint.
• NEBASULF: Neomycin sulph. 5 mg, bacitracin 250
U, sulfacetamide 60 mg/g oint. and powder for
surface application.

23. MACROLIDE ANTIBIOTICS
• These are antibiotics having a macrocyclic lactone ring with attached
sugars. Eg,: Erythromycin
• The macrolide antibiotics have three common chemical characteristics
(a) a large lactone ring (which prompted the
name macrolide)
(b) a ketone group, and
(c) a glycosidically linked amino sugar.
MOA: It prevents the translocation step of bacterial protein synthesis.
Uses: Drug of choice for pneumonia in children.
Diphtheria, Pertusis, Gastroenteritis, Syphilis, Upper respiratory Tract
infections and acne.

24. ERYTHROMYCIN
• Erythromycin may be bacteriostatic or bactericidal depending on the organism and drug
concentration.
• PP:
i) White or slightly yellow crystals or powder ii) Odorless iii) Bitter in taste iv) Slightly soluble in
water. v) Soluble in alcohols vi) Insoluble in ether.
Stability: Slightly hygroscopic. Stored in well closed containers.
BRANDS:
1. Erythromycin (base): ERYSAFE 250, mg tabs, EROMED 333 mg tab, 125 mg/5 ml susp.
2. Erythromycin stearate: ERYTHROCIN 250, 500 mg tab, 100 mg/5 ml susp., 100 mg/ml ped.
drops. ETROCIN, ERYSTER 250 mg tab, 100 mg/5 ml dry syr.
3. Erythromycin estolate: ALTHROCIN 250, 500 mg tab, 125 mg kid tab, 125 mg/5 ml and
250 mg/5 ml dry syr, 100 mg/ml ped. drops, E-MYCIN 100, 250 mg tab, 100 mg/5 ml dry syr,
EMTHROCIN 250 mg tab, 125 mg/ 5 ml dry syr.
4. Erythromycin ethylsuccinate: ERYNATE 100 mg/5 ml dry syr, ERYTHROCIN 100 mg/ml
drops, 125 mg/5 ml syr.