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The term antibiotic has its origin in the word antibiosis (i.e. against life). Antibiotics
are chemical substances obtained from various species of microorganisms (bacteria,
fungi, actinomycetes) that suppress the growth of other microorganisms and
eventually may destroy them. The probable points of difference amongst the
antibiotics may be physical, chemical, pharmacological properties, antibacterial
spectra, and mechanism of action. They have made it possible to cure diseases
caused by bacteria, such as pneumonia, tuberculosis, and meningitis, and they save
the lives of millions of people around the world.


Antibiotics are classified on the basis of their mechanism of action and by its
chemical nature.

Classification Based on

Mechanism of Action

1. Agents that inhibit the synthesis of bacterial cell wall: These include the
penicillins and cephalosporins that are structurally similar and dissimilar agents,
such as cycloserine, vancomycin, bacitracin and the imidazole antifungal agents.

2. Agents that act directly on the cell membrane of the microorganisms, affecting
permeability, and leading to leakage of intracellular compounds: These include
polymyxin, polyene antifungal agents, nystatin, and amphotericin B that bind to cell
wall sterols.

3. Agents that affect the function of 30s and 50s ribosomal subunits to cause
reversible inhibition of protein synthesis: These include tetracyclines,
erythromycins, chloramphenicol, and clindamycin.

4. Agents that bind to the 30s ribosomal subunit and alter protein synthesis: These
include aminoglycosides that leads to cell deaths eventually.

5. Agents that affect nucleic acid metabolism: Such as rifamycins, which inhibit
DNA dependent RNA polymerase.


Classification Based on Chemical Structure

1. β-lactam antibiotics

2. Aminoglycoside antibiotics

3. Tetracycline antibiotics

4. Polypeptide antibiotics

5. Macrolide antibiotics

6. Lincomycins

7. Other antibiotics


1. β-lactam antibiotics

These consists of two major class of agents, that is penicillins and cephalosporins.

a. Penicillins:

Penicillin, the most important antibiotic, was first extracted from the mould
Penicillium notatum. Subsequently, a mutant of a related mould, P. chrysogenum,
was found to give the highest yield of penicillin and is employed for the commercial
production of this antibiotic. Penicillin belongs to a group of antibiotics called β-
lactam antibiotics . The basic structure of the penicillins consists of a thiazolidine
ring fused with a β-lactam ring, which is essential for antibacterial activity. These
two rings constitute the fundamental nucleus of all the penicillins, namely, 6-amino
penicillanic-acid (6-APA) A variety of semisynthetic penicillins are produced by
altering the composition of the side chain attached to 6-APA nucleus. Both the 6-
APA nucleus and side chain are essential for the antibacterial activity.




Penicillins are named in the following ways:

a. Chemical abstract

1. The penicillins are described as 4-thia-1-azabicyclo (3.2.0) heptanes.

2. Benzylpenicillin is 6-(2-phenylacetamido)-3, 3-dimethyl-7-oxo-4-thia-1-
azabiclo(3.2.0)heptane2-carboxylic acid.

b. Penam: In order to simplify the unsubstituted bicylic ring system of penicillin, it
is given the name penam. Accordingly, the penicillins are 6-acylamino-2, 2-dimethyl





I. Penicillinase-susceptible penicillins

The general impact on antibacterial activity is as follows:

• Good gram-positive potency against susceptible Staphylococci and Streptococci

• Useful against some gram-positive cocci

• Not effective against gram-negative bacilli



II. Penicillinase-resistant penicillins

General impact on antibacterial activity is as follows:

• Decreased susceptibility to many penicillinase.

• Active against microrganisms, resistant to early penicillin.

• Oxacillins offer good oral activity.





III. Aminopenicillins












General impact on antibacterial activity is as follows:

• Extended spectrum of activity against some gram-negative bacteria and retention
of gram-positive potency

• Ineffective against Pseudomonas aeruginosa

IV. Antipseudomonal penicillins (Carboxy Penicillins)

V. Ureidopenicillins


Mode of action:

The cell wall of bacteria is essential for the normal growth and development.
Peptidoglycan is a heteropolymeric component of the cell wall that provides rigid
mechanism for stability by virtue of its highly cross-linked lattice-wise structure.
The peptidoglycan is composed of glycan chains, which are linear strands of two
alternating amino sugars (N-acetyl glucosamine and N-acetylmuramic acid) that are
cross-linked by peptide chains of an enzyme, transpeptidase. Penicillins inhibit the
transpeptidase activity to the synthesis of cell walls. They also block cleavage of
terminal D-alanine during the cell wall synthesis. The biosynthesis of peptidoglycan
involves three stages Β-lactam antibiotics inhibit the last step in peptidoglycan
synthesis. The transpeptidase enzyme that contains serine is probably acylated by β-
lactam antibiotics with the cleavage of -CO-N-bond of the βlactam ring. This renders
the enzyme inoperative and inhibits peptidoglycan synthesis.


6-Acyl side chain:


The substitution of R on the primary amine with an electron withdrawing group
decreases the electron density on the side chain and protects from acid degradation.
Substituents on the α-carbon of the side chain, such as amino (ampicillin), chloro,
and guanidine exerts good resistance to inactivation by acids. Benzyl penicillin
undergoes acid and alkali degradation and is susceptible to all known DŽ-lactamase.
The increased latitude in varying the acyl amino side chain through acylation of
6APA results with superior biological activity. Substitution of α-aryl of the alkyl
group in the side chain gives increased stability and oral absorption.

1. Substitution of bulky groups on α-carbon of the side chain confers β-lactamase
resistance. Examples: methicillin, nafcillin, oxacillin, etc. In all these penicillins, an
aromatic ring is attached directly to the side chain amide carbonyl, and there is
substitution at both positions ortho to the point of attachment. The size of the ring
systems play an important role in determining the ability of the ortho substitutent to
confer penicillinase resistance.

2. The isomeric forms of penicillins differs in their activity. Example: D-isomer is
2–8 times more active than L-isomer of amoxicillin. The introduction of polar group
or ionized molecule into the α-position of the side chain in the benzyl carbon atom
of penicillin-G confers against the gram-negative bacilli. Amino, hydroxyl,
carboxyl, and sulphonyl increases gram-negative activity. Example: ampicillin and

3. Replacement of acyl side chain with hydroxymethyl groups shows improved
gram-negative activity and introduction of C-6 α-methoxy group produces greater
stability against β-lactamase. N-acylated ampicillins (ureidopenicillins) have
increased activity against Pseudomonas.

4. Many esters of the carboxyl group attached to C-3 have been prepared as prodrugs
to increase lipophilicity and acid stability. Example: Acetoxymethyl ester
derivatives are used for preparing prodrugs.

5. The sulphur of the thiazolidine ring with O, CH2, and CH-β-CH3 gives broad-
spectrum antibacterial activity. The geminal dimethyl group at C-2 position is a
characteristic of the penicillin. In general, derivatization of the C-3 carboxylic acid
functionality is not tolerated unless the free penicillin carboxylic acid can be
generated in vivo. Doubly activated penicillin esters, undergo rapid cleavage in vivo
to generate active penicillin. Example: pivampicillin and becampicillin. The
antibacterial activity is evidented by N-4 atom at ring junction.


6. In vitro degradation is retarded by keeping the pH of the solution between 6.0 and
8.0. More lipophilic side chain increases the plasma protein binding. Example:
Ampicillin: 25% plasma protein bound and phenoxy methyl penicillin: 75% plasma
protein bound.

I. Penicillinase resistant penicillins

i. Methicillin


ii. Oxacillins (Isoxazolyl penicillins)

Properties and uses:

Oxacillin sodium monohydrate is a white powder, soluble in water and methanol,
insoluble in methylene chloride. The use of oxacillin and other isoxazolyl penicillins
should be restricted to the treatment of infections caused by Staphylococci that are
resistant to penicillin G, although their spectrum of activity is similar to that of
penicillin G.




The cephalosporins were isolated from the fungus Cephalosporium acremonium in
1948 by Pro Tzu, Newton, and Abraham (1953). The main product being
cephalosporin-C, the molecular modifi cation of cephalosporin-C gave origin to
semisynthetic substances. They are β-lactam antibiotics with same fundamental
structural requirements as penicillins, the main difference between the two is that
cephalosporins contain dihydrometathiazine ring, while penicillin contains a
tetrahydrothiazole (thiazolidine) ring. The cephalosporins are much more acid stable
than the corresponding penicillins and also have a mechanism of action similar to
that of penicillins; they mainly inhibit the cross-linking of the peptidoglycan units in
bacterial cell walls by inhibiting transpeptidase enzyme. However, they bind in the
target proteins other than penicillins binding proteins.

Cephalosporins can be divided into three classes:


1. Cephalosporin N: It has a penicillin-like structure being a derivative of 6-
aminopenicillanic acid.

2. Cephalosporin P: An acidic antibiotic, which is steroidal in nature.

3. Cephalosporin-C: It is a true cephalosporin and it is a derivative of 7 amino-
cephalosporanic acid.


Cephalosporins are named in the following ways:

1. Chemical abstracts: 5-Thia-1-azobicyclo (4.2.0) octanes. Accordingly,
cephalothin is 3-(Acetoxy methyl)-8-oxo-7-(2-thienyl) acetamido-5thia-1-aza-
bicyclo[4.2.0]-oct-2ene-2-carboxylic acid.

2. Cepham derivatives: Cepham is the name given to the unsubstituted bicyclic

Classification Cephalosporins are classifi ed on the basis of their chemical structure,
clinical pharmacology, antibacterial spectrum, or penicillinase resistance.

a. Orally administered: cephalexin, cephradine, and cefaclor

b. Parentrally administered: cephalothin, cephapirin, cephacetrile, and cefazedone.
These agents are sensitivity to β-lactamase

c. Resistant to β-lactamase and parentrally administered: cefuroxime, cefamandole,

d. Metabolically unstable: cephalothin and cephapirin

Clinically used cephalosporins:


I. First-generation cephalosporins

These drugs have the highest activity against gram-positive bacteria and the lowest
activity against gram negative bacteria

II. Second-generation cephalosporins

These drugs are more active against gram-negative bacteria and less active against
gram-positive bacteria than first-generation members

III. Third-generation cephalosporins

These drugs are less active than first-generation drugs against gram-positive
organisms, but have a much expanded spectrum of activity against gram-negative

IV. Fourth-generation cephalosporins

Cefepime and cefpirome are new fourth-generation parenteral cephalosporins with
a spectrum of activity which makes them suitable for the treatment of infections
caused by a wide variety of bacteria




Properties and uses:

Cephalexin monohydrate is a white crystalline powder, sparingly soluble in water,
and practically insoluble in alcohol. The α-amino group of cephalexin renders it acid
stable. The 3-methyl group is responsible for the metabolic stability. It is particularly
recommended for urinary tract infection.

Dose: The oral dose for adults is 250–500 mg every 6 h, for children, the dose is 18–
25mg/kg every 6 h.

ii. Cefadroxil (Cefadrox, Droxyl, Codroxil)



Properties and uses:

Cefadroxil monohydrate is a white or almost white powder, slightly soluble in water,
and sparingly soluble in ethanol. The antibacterial spectrum of action and therapeutic
indications of cefadroxil are very similar to those of cephalexin and cephradine. The
D-p-hydroxyphenylglycyl isomer is much more active than the L-isomer.


It is assayed by adopting liquid chromatography technique.

Dosage forms:


Cefadroxil capsules I.P., B.P., Cefadroxil oral suspension I.P., B.P. Cefadroxil
tablets I.P.


In the case of uncomplicated lower urinary tract infections: For adults, the dose is
1–2 g daily as a single or 2 divided doses. For children more than 6 years, the dose
is 500 mg twice a day, that is, 1–6 years, 250 mg twice a day; for children less than
1 year, the dose is 25 mg/kg daily in divided doses. In the case of skin and skin
structure infections: For adults, the dose is 1g per day in single or divided doses. For
children, the dose is 30 mg/kg per day in equally divided doses every 12 h. In the
case of pharyngitis and tonsilitis: For adults in the treatment of group A beta-
haemolytic streptococcal pharyngitis and tonsilitis, the dose is 1 g per day in single
or divided doses for 10 days. In the case of children, 30 mg/kg per day in equally
divided doses every 12 h for at least 10 days.


Cephalothin is a white, odourless, crystalline powder, insoluble in most organic
solvents, soluble in organic solvents and it is acid stable. It is hygroscopic and
decomposes on heating, and it has been described as broad-spectrum antibacterial
compound, it is not in the same class as the tetracyclines. Its spectrum of activity is
broader than that of penicillin G and more similar to that of ampicillin.


The dose for adults given IM or IV is equivalent to 500 mg–1 g every 4 to 6 h;
children the dose is 13–26 mg/kg of body weight every 4 h.



Adverse reactions of the cephalosporins

The cephalosporins produce a number of adverse effects. Examples are the

i. Allergic manifestation: The cephalosporins should be avoided or used with caution
in individuals allergic to penicillins. When cefamandole or cefoperazone is ingested
with alcohol, a disulphiramlike effect is seen, because these cephalosporins block
the second step in alcohol oxidation, which results in the accumulation of

ii. Bleeding: Bleeding can occur with cefemandole or ceforperazone because of
antivitamin K effects. But the administration of the vitamin overcomes this problem.



The aminoglycoside antibiotics contain one or more amino sugars linked to an
aminocytitol ring by glycosidic bonds. These are broad-spectrum antibiotics; in
general, they have greater activity against gram-negative than gram-positive


bacteria. The development of streptomycin, the fi rst antibiotic of this group, was a
well-planned work of Waksman (1944) and his associates, who isolated it from a
strain of Streptomyces griseus. The aminoglycoside can produces severe adverse
effects, which include nephrotoxity, ototoxicity, and neuro effects. These properties
have limited the use of aminoglycoside chemotherapy to serious systemic
indications. Some aminoglycosides can be administered for ophthalmic and topical

Mode of action:

The aminoglycosides exhibit bactericidal effects as a result of several phenomena.
Ribosomal binding on 30s and 50s subunits as well as the interface produces
misreading; this disturbs the normal protein synthesis. Cell membrane damage also
plays an integral part in ensuring bacterial cell death.


SAR of Aminoglycoside Antibiotics

The aminoglycosides consist of two or more amino sugars joined in glycoside
linkage to a highly substituted 1,3-diaminocyclo hexane (aminocyclitol), which is a
centrally placed ring. The ring is a 2-deoxy streptamine in all aminoglycosides
except streptomycin and dihydrostreptomycin, where it is streptidine.


• In kanamycin and gentamycin families, two amino sugars are attached to 2-deoxy

• In streptomycin, two amino sugars are attached to strepidine.


• In neomycin family, there are amino sugars attached to 2-deoxy streptamine. The
aminoglycoside antibiotics contain two important structural features. They are
amino sugar portion and centrally placed hexose ring, which is either 2-
deoxystreptamine or streptidine.


Tetracyclines have a ring system of four linear annelated six-membered rings and
are characterized by a common octahydronaphthacenes skeleton. They are potent,
broad-spectrum antibacterial agents effective against gram-positive and gram-
negative aerobic and anaerobic bacteria. As a result, the tetracyclines are drugs of
choice or well-accepted alternatives for a variety of infectious diseases. Among
these, they also play a role in the treatment of sexually transmitted and gonococcal
diseases, urinary tract infections, bronchitis, and sinusitis remain prominent. The
majority of the marketed tetracyclines (tetracycline, chlorotetracycline,
oxytetracycline, and demeclocycline) are naturally occurring compounds obtained
by the fermentation of Streptomyces spp. broths. The semisynthetic tetracyclines
(methacycline, doxycycline, minocycline) have the advantage of longer duration of
antibacterial action. However, all these tetracyclines exhibit a similar profile in terms
of antibacterial potency. In general, their activity encompasses many strains of gram-
negative E. coli, Proteus, Klebsiella, Enterobacter, Niesseria, and Serratia spp., as
well as gram-negative Streptococci and Staphylococci of particular interest is the
potency of tetracylines against Haemophilus, Legionella, Chlamydia, and

Classes of tetracyclines

I. Natrual tetracyclines (biosynthetic)

II. Semisynthetic tetracyclines

III. Protetracyclines


I. Natrual tetracyclines (biosynthetic) :





Properties and uses:

Methacycline is a yellow crystalline powder, sparingly soluble in water. It is
obtained by the chemical modification of oxytetracycline. It has an antibiotic


spectrum similar to tetracyclines, but greater potency; about 600 mg of methacycline
is equivalent to 1 g of tetracycline.

Properties and uses:

It was first obtained in small yields by a chemical transformation of oxytetracycline.
The 6α-methyl epimer is more than three times as active as its β epimer.


In adults, the oral dosage is 100 mg every 12 h.

Dosage forms:

Doxcycline HCl capsules I.P., Doxcycline HCl tablets I.P.



The key structural feature is a linearly fused tetracyclic nucleus and each ring needs
to be six membered and purely carbocyclic. A tetracyclic backbone skeleton is
essential for activity.

• The D-ring needs to be aromatic and the A-ring must be appropriately substituted
at each of its carbon atoms for notable activity.


• The B-ring and the C-ring tolerate certain substitutent changes as long as the keto-
enol systems (at C-11, 12, 12a) remain intact and conjugated to the phenolic D-ring.

• The D, C, B-ring phenol, keto-enol system is imperative and the A-ring must also
contain a conjugated keto enol system.

• Specifically, the A-ring contains a tricarbonyl derived keto-enol array at positions
C-1, 2, and -3. Other structural requirements for good antibacterial activity include
a basic amine function at C-4 position of the A-ring.

Modification of C-1 and C-3 position: The keto-enol tautomerism of ring A in carbon
atom 1 and 3 is a common feature to all biologically active tetracyclines, blocking
this system by forming derivatives at C-1 and C-3 results in loss of antibacterial
activity A–C = O, a function of C-1 and C-3 is essential for activity. In addition,
equilibrium between non-ionized and Zwitterionic structure of tetracycline is
essential for activity.

Modification of C-2 position: The antibacterial activity resides on the carboxamide
moiety. The amide is best left unsubstituted or monosubstitution is acceptable in the
form of activated alkylaminomethyl amide (Mannich bases). An example includes
rolitetracycline large alkyl group on the carboxamide that may alter the normal keto-
enol equilibrium of the C-1, 2, and 3 conjugated systems and diminishes inherent
antibacterial activity. The replacement of carboxamide group or dehydration of
carboxamide to the corresponding nitrile results in a loss of activity.

Modification of C-4 position: The keto-enolic character of the A-ring is due to the
α-C-4 dimethyl amino substituent. Loss of activity is exerted when dimethyl amino
group is replaced with hydrazone oxime or hydroxyl group.

Modification of C-4a position: The α-hydrogen at C-4a position of tetracyclines is
necessary for useful antibacterial activity.

Modification of the C-5 and C-5a positions: Alkylation of the C-5 hydroxyl group
results in loss of activity. Naturally occurring antibacterial tetracyclines have an
unsubstituted methylene moiety at the C-5 position. However, oxytetracycline
contains C-5 α-hydroxyl group, was found to be a potent compound, and has been
modified chemically to some semisynthetic tetracyclines. Esterification is only
acceptable if the free oxytetracycline can be liberated in vivo; only small alkyl esters
are useful. Epimerization is detrimental to antibacterial activity.


Modification at the C-6 position: The C-6 methyl group contributes little to the
activity of tetracycline. The C-6 position is tolerant to a variety of substituents. The
majority of tetracyclines have α-methyl group and α β-hydroxyl group at this
position. Demeclocyclin is a naturally occurring C-6 demethylated chlortetracycline
with an excellent activity. Removal of C-6 hydroxyl group affords doxycycline,
which exerts good antibacterial activity.

C-7 and C-9 substituents: The nature of the aromatic D-ring predisposes the C-7
position to electrophilic substitution. Substitution with electron withdrawing group
such as nitro and halogen groups are introduced

4. Polypeptide antibiotics

The compounds have complex polypeptide structure. These are resistant to animal
and plant proteases. These contain lipid moieties besides amino acids that are not
found in peptides of animal and plant origins. Examples: bacitracin, polymycin,
amphomycin, tyrothricin, and vancomycin.

Properties and uses:

Bacitracin is a white hygroscopic powder, soluble in water and alcohol. Bacitracin
antibiotic is isolated from the fermentation broth of a culture of tracyl-1 strain of
Bacillus subtilis. It is found to be a complex mixture of at least 10 polypeptides (A,
A1, B, C, D, E, F1, F2, F3, and G), of which bacitracin A fraction is believed to be
the most abundant and the most potent. A divalent ion Zn++ enhances its activity.
Although bacitracin is occasionally employed for topical application (often in
combination with neomycin, polymycin, and tyrothicin) for the treatment of burns,


ulcer, and wounds, it can cause serious necrosis of the kidney tubules; if it is given
systematically (i.e. I.V route) an oral administration is not feasible due to its lack of
absorption from the GI tract. A variety of gram-positive cocci and bacilli are
sensitive to bacitracin. It should be stored in airtight containers due to its hygroscopic


It is assayed by microbiological method.


Properties and uses:

Polymycin sulphate is a white hygroscopic powder, soluble in water, and slightly
soluble in ethanol. The polymyxins are cyclic peptides holding a fatty acid side
chain. This is a group of relatively simple basic, cationic, detergent peptides that are
produced by Bacillus polymyxia. At least, fi ve polymyxins (A, B, C, D, and E) are
known, but only polymyxin B and polymyxin E are of clinical utility. Both
polymyxin B and polymyxin E (colistin) are mixtures of two components and is used
in the treatment of bacterial meningitis, urinary tract infection, burns, wounds, and
gastroenteritis. Polymyxin may affect renal tubules and central nervous system
(CNS), and because of their nephrotoxicity associated with their systemic use, they
are primarily employed to treat topical infections.


It is assayed by adopting liquid chromatography technique.



The macrolide antibacterial agents are extremely useful chemotherapeutic agents for
the treatment of a variety of infectious disorders and diseases caused by a host of
gram-positive bacteria, both cocci and bacilli; they also exhibit useful effectiveness
against gram-negative cocci, specially, neisseria spp. The macrolides are commonly
administered for respiratory, skin, tissue, and genitourinary infections caused by
these pathogens.


They are characterized by five common chemical features.

1. A macrocyclic lactone usually has 12–17 atoms, hence the name macrolide.

2. A ketone group.

3. One or two amino sugars glycosidically linked to the nucleus.

4. A neutral sugar linked either to amine sugar or to nucleus.

5. The presence of dimethyl amino moiety on the sugar residue, which explains the
basicity of these compounds, and consequently the formation of salts. The
antibacterial spectrum of activity of the more potent macrolides resembles that of
penicillin. Examples: erythromycin, oleandomycin, clarithromycin, flurithromycin,
dirithomycin, azithromycin.


Properties and uses:

Azithromycin is a white powder, practically insoluble in water, soluble in anhydrous
ethanol and methylene chloride. It is very stable under acidic conditions, is less


active against Streptococci and Staphylococci than erythromycin, and is far more
active against respiratory infections due to H. influenzae and Chlamydia trachomatis

Mode of action:

Macrolide antibiotics are bacteriostatic agents that inhibit protein synthesis by
binding irreversibly to a site on the 50S subunits of the bacterial ribosome. Thus,
inhibiting the translocation steps of protein synthesis at varying stages of peptide
chain elongation (hinder the translocation of elongated peptide chain back from ‘A’
site to ‘P’ site). The macrolides inhibit ribosomal peptidyl transferase activity. Some
macrolides also inhibit the translocation of the ribosome along with the mRNA

Properties and uses:

The antibiotic lincomycin is obtained from Actinomycetes, Streptomyces, and
Lincolnensis. The ability of lincomycin to penetrate into bones, adds to its qualities
and it gets promoted in the chemotherapy of bone and joint infections by penicillin
resistant strains of S. aureus. Variation of the substituents on pyrrolidine portion and
C-5 side chain affects the activity.

Some of the examples are as follows:

i. N-demethylation imparts activity against gram-negative bacteria.

ii. Increase in the chain length of the propyl substitutent at C-4 position in pyrrolidine
moiety up to n-hexyl increase in vivo activity.

iii. The thiomethyl ether of α-thiolincosamide moiety is essential for activity.


iv. Structural modifications at C-7 position, such as introduction of 7S chloro or 7R-
OCH3, change the physiochemical parameters of the drug (i.e. partition coefficient),
and thus, alter the activity spectrum and pharmacokinetic properties. The usual side
effects include skin rashes, nausea, vomiting, and diarrhoea. Dosage forms:
Lincomycin HCl capsules I.P.


Examples of other antibiotics are chloramphenicol, rifampicin and mupirocin.

Chloramphenicol or chloromycetin Chloramphenicol has a spectrum of activity
resembling that of the tetracyclines except that it exhibits a bit less activity against
some gram-positive bacteria. It is isolated from Salmonella venezuelae by Ehrlich et
al in 1947. It contains chlorine and is obtained from an actinomycete, and thus,
named as chloromycetin. It is specifically recommended for the treatment of serious
infections caused by H. influnzae, S. typhi (typhoid), S. pneumoniae, and N.
meningitides. Its ability to penetrate into the CNS presents an alternative therapy for
meningitis and exhibits antirickettsial activity.



Properties and uses:

Chlorampenicol is a white or greyish-white or yellowish-white crystalline powder
or fi ne crystals, slightly soluble in water, soluble in alcohol and propylene glycol. It
was the first, and still is the only therapeutically important antibiotic to be produced
in competition with microbiological processes. It contains a nitrobenzene moiety and
is a derivative of dichloroacetic acid. Since it has two chiral centres, four isomers
are possible. The D-(-) threo is the biologically active form. It is used in the treatment
of typhoid fever caused by S. typhi. The most serious adverse effect of
chloramphenicol is bone marrow depression and fatal blood dyscrasias.



Dissolve the sample in water, dilute with the same solvent, and measure the
absorbance at the maximum of 278 nm using ultraviolet spectrophotometer.


Dose: Usual adult dose is 500 mg every 6 h.

Dose: Usual adult dose is 500 mg every 6 h.

Dosage forms: Chloramphenicol capsules I.P., B.P., Chloramphenicol ear drops I.P.,
B.P., Chloramphenicol eye ointment I.P., B.P., Chloramphenicol eye drops B.P








 Types
 synthesis
 mechanism
 uses
 dose
 adverse effect



 Antineoplastic agents are drugs used for the treatment of cancer, malignancy,

tumour, carcinoma, sarcoma, leukaemia, or neoplasm (Greek neo = new,

Plasm = formation).

 Neoplasm refers to a group of diseases caused by several agents, namely,

chemical compounds and radiant energy.

 Cancer is characterized by an abnormal and uncontrolled, division of cells,

which produces tumours and invades adjacent normal tissues.

 Often, cancer cells separate themselves from the primary tumour, and are

carried by the lymphatic system to reach distant sites of the organs, where they

divide and form secondary tumours (metastasis).

Cell Cycle Kinetics Two key aspects of cellular life are the following:


1. DNA synthesis and mitosis to produce new cells.

2. Cell differentiation that produces specialized cells.

Limitations of Therapy

• Cancer cells very rapidly develop resistance to antineoplastic drugs.

• Differences between normal and neoplastic human cells are merely quantitative.

• Biochemical and morphological differences between normal and neoplastic cells
are slight; therefore, antineoplastic agents are devoid of selective toxicity to tumour

• Antineoplastic agents kill cells by first -order kinetics, that is, they kill a constant
fraction of cells. However, some of the cancer cells elude killing and one of these
cells may restablize the tumour. It is extremely difficult to kill all the malignant cells.

• Most antineoplastic drugs are highly toxic to the patients.

Adverse Effects

The prominent adverse effects of antineoplastic drugs are exerted on rapidly
proliferating normal tissues, in addition, to their chronic and cumulative toxicities.

• Bone marrow toxicity: Bleomycin, L-asparaginase.

• Hair follicle toxicity: Methotrexate, Vincristine, Cyclophosphamide, and

• Hepatotoxicity: Azathiopurine, Mercaptopurine, and L-asparaginase.

• Skin rashes: Vinca alkaloids, Nitrosourea, Anthracyclins, and Mitomycin C.

• Pulmonary toxicity: Bleomycin, Methotrexate, and Busulfan.

• Cardiac toxicity: Doxorubicin, Daunorubicin, and Anthracyclins.

• Other toxicities: Intestinal epithelium, central nervous system (CNS) toxicity,
nephrotoxicity, immunosuppression, fever, anaphylaxis, cataracts, haemolytic
anaemia, pancreatitis, pituitary insufficiency, adrenal insufficiency, coagulation
problems, suppression of growth, and carcinogenicity.


Antineoplastic agents are classified as follows:


 Alkylating agents

 Antimetabolites

 Antibiotics

 Plant products

 Enzymes

 Hormones

 Immuno therapy

 Monoclonal antibodies

 Radio-therapeutic agents

 Cyto-protective agents

 Miscellaneous.




Alkylating agent

N i t r o g e n m u s t r a d s


A lk y l S u l p h o n a t e


N it r o s o u r e a s

a l k y l a t i n g a g e n t s

A z i r i d i n e s










Nitrogen mustards



b.Alkyl Sulphonate

Busulfan CH3SO2O(CH2)4OSO2CH3



c. Nitrosoureas

d. Aziridines

1,-(2,4-dinitro phenyl) aziridine

e. Altretamine


4 (1-aziridinyl)-2,6-dimethoxy triazine


Triethylene melamine

f. Methylhydrazines




I. Alkylating agents

Step I: Intramoleular cyclization


Step II: Nucleophilic attack of unstable aziridine

Mode of action: These compounds produce highly reactive carbonium ion
intermediates that transfer alkyl group to cellular macromolecules by forming
covalent bonds. It alkylates the 7th nitrogen atom of guanine residue in DNA, and
results in cross-linking or abnormal base pairing. Initially, one of the 2-chloro ethyl
side chain undergoes a fi rst-order (SN1) intramolecular cyclization with the release
of Cl– and formation of highly reactive ethyleniminium intermediate (Step I) By this
reaction, tertiary amine is converted to an unstable quaternary ammonium
compound, which react by forming carbonium ion. This precedes a second-order
reaction (SN2) nucleophilic substitution and alkylates the 7th N atom in guanine
(Step II).

I. a. Nitrogen mustards Mechlorethamine (Mustargen, Nitrogen mustard, Mustine)


Properties and uses: It is a white crystalline hygroscopic powder, soluble in water
and in alcohol. It is used in Hodgkin’s disease in combination with vincristine,
procarbazine, and prednisone. Most serious toxic reaction is bone marrow
depression, which results in leukopenic and thrombocytopenia.

Dose: Single doses of 400 μg per kg body weight or a course of 4 daily doses of
100 μg per kg is normally administered by intravenous (IV) injection in a strength
of 1 mg per ml in sodium chloride injection.


Properties and uses:

Melphalan is a white powder, practically insoluble in water and ether, slightly
soluble in methanol and dissolves in dilute mineral acids. Melphalan is active against
multiple myeloma, breast, testicular, and ovarian carcinoma.


To the sample add 20% w/v solution of potassium hydroxide, heat on a water bath,
add water and nitric acid, cool, and titrate with 0.1 M silver nitrate. Determine the
end point potentiometrically.



Dose orally is 150 μg per kg body weight daily for 4–7 days combined with
prednisone 40–60 mg daily; 250 mg per kg daily for 4–5 days; or 6 mg daily by 2–
3 weeks. Dosage forms: Melphalan injection I.P., B.P., Melphalan tablets I.P., B.P.


I. b. Alkyl sulphones

Busulfan (mylearn)


1,4-Bis(methanesulphonyloxy) butane







Busulfan undergoes sulphur stripping due to interaction with thiol compounds such
as glutathione or cysteine and leads to loss of two equivalents of methosulphonic
acid and formation of cyclic sulphonium intermediates, which is then converted into
a metabolite 3-hydroxythiolane-1, 1-dioxide.

Properties and uses:

Busulfan is a white crystalline powder, very slightly soluble in water and alcohol,
soluble in acetone and acetonitrile. It is used in the treatment of chronic granulocytic


To the sample add water, boil under a refl ux condenser, cool and titrate with 0.1 M
sodium hydroxide using phenolphthalein as indicator until a pink colour is obtained.


For granulocytic leukaemia, the daily oral dose is 60 μg per kg body weight, up to
a maximum single daily dose of 4 mg, and to be continued till the white cell count
falls between 15,000 and 25,000 per mm3

Dosage forms:

Busulfan tablets I.P., B.P.

I.c. Nitrosourea




Properties and uses:

Carmustine is a yellowish granular powder, very slightly soluble in water, very
soluble in methylene chloride, and soluble in ethanol. It is used against brain tumours
and leukaemia, which have metastasized to the brain, and these multiple states
respond to a combination of carmustine and prednisone.


Dissolve the sample in ethanol, dilute with water, and measure the absorbance at the
maxima at 230 nm using ultraviolet spectrophotometer

I. d. Aziridines





Thiotepa undergoes oxidative desulphuration forming an active cytotoxic metabolite
known as Triethylene phosphoramide (TEPA). Aziridine metabolism occurs, with
liberation of ethanolamine. Properties and uses: Thiotepa exists as white crystalline
flakes, freely soluble in water, chloroform, and ethanol. It is used as cytotoxic
alkylating agent.


Transfer the sample to an iodine fl ask with the aid of 20% w/v solution of sodium
thiosulphate and titrate immediately with 0.1 M hydrochloric acid, using methyl
orange as indicator, until a faint red colour persists for 10 sec. Stopper the flask,
allow to stand for 30 min, and titrate with 0.1 M sodium hydroxide using
phenolphthalein as indicator. Subtract the volume of 0.1 M sodium hydroxide used
from the volume of 0.1 M hydrochloric acid used.

Dosage forms:

Thiotepa injection I.P., B.P.


I.e Altretamine



I.e. Methyl hydrazines


Properties and uses:

It exists as white to pale yellow crystalline powder with a slight odour and a bitter
taste, soluble in water or alcohol, slightly soluble in chloroform, but insoluble in
ether. Solutions are acid to litmus, stable in light, slowly oxidized in air, and stable
at room temperature (in the presence of oxygen, oxidation is accelerated by
increased temperature).








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Medicinal chemistry pharm.D Ilango valentina