Download Antibiotics *part 2

Antibiotics II
Beta-Lactam Antibiotics
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They have β-lactam heterocyclic nucleus consists of a
4-membered cyclic ring with a N-atom.
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The highly-strained β-lactam nucleus is stabilized by
means of the fusion of a variety of either 5-membered or
6-membered heterocyclic moieties to give rise to a wide
spectrum of newer antibiotics.

Beta-Lactam antibiotics inhibit the formation of the
structure peptidoglycan of the bacterial cell wall.

As this component is absent in mammalian cells, BetaLactam antibiotics have very low toxiciy towards
mammailian.
Beta-Lactam antibiotics essentially comprise of :
 Penicillins
 Cephalosporins
 Imipenem,
 Nocardicin A,
 Monobactem ,
 Clavulanic acid,
 Moxalactam, and
 Thienamycin
General structure of
penicillin
Production of antibiotics
In general, the antibiotics are produced on a large scale by
three known methods, namely:
(a) fermentation process.
(b) semi-synthetic process : in which the products obtained
by fermentation are modified by chemical addition of side
chain .
(c) synthetic process.
Production of Penicillin
• Now
most
antibiotics
including
penicillin
are produced by staged
fermentations in which strains of
microorganisms producing high yields
are grown under optimum conditions
• nutrient media
• fermentation tanks holding several
thousand gallons.
• Penicillin is produced by the fungus
Penicillium chrysogenum which requires
sugars, and a source of nitrogen in the
medium to grow well.
• Like all antibiotics, penicillin is a
secondary metabolite, so is only
produced in the stationary phase.
 When penicillin was first made at
the end of the second world war
using the fungus Penicilium notatum,
the process made 4 mg L-1.
Penicilium notatum
 Today, using a different species (P.
chrysogenum) and a better extraction
procedures the yield is 40 mg L–1.
P. chrysogenum
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Penicillin production
 The microorganism culture is developed first in the lab by the
addition of Penicillium chrysogenum spores into a liquid medium.
When it has grown to the acceptable amount, it is inoculated into
the fermenter , the inoculum sholud represent 5-10% of the volume
of fermenter which contains the culture medium.
 culture medium consists of :
 Source of carbon nutrition: – e.g., lactose and glucose;
 Nitrogen sources: – e.g., corn steep liquor;
 Phosphate buffer: – to provide P in the medium and also to maintain
the pH of the medium.
 The medium is constantly aerated and agitated.
 Typical parameters such as pH, temperature, stirrer speed and
dissolved oxygen concentration, are observed
 There are two important and distinct phases normally
encountered in the fermentative process, namely:
(a) Growth Phase of the Organism: It is also sometimes
referred to as the ‘trophophase’; wherein the number of
organisms per unit time increases progressively (30-40
hours)
(b) Idiophase of the Organism: In the idiophase there is a
substantial antibiotic production; and hence, invariably
termed as the ‘antibiotic production phase’. (5-7 days)
 In the ‘growth phase’, the culture becomes thick by virtue of the
formation of ‘aggregates of fungal cells’ usually known as mycelium.
 Glucose is preferentially consumed as compared to lactose specifically in
the ‘growth phase’, as it may be employed as a prime source of C
directly,
 However , the glucose gets fully utilized, and subsequently the fungus
makes use of ‘lactose’ as a source of C.
 Interestingly, no additional growth takes place as the lactose cannot be
used as such unless and until it gets converted to glucose and galactose
via hydrolysis.
 Hence the decreased availability of C in the medium obviously offers a
‘triggering mechanism’ in the production of penicillin.
•
 After growth phase penicillin production phase occurs.
and penicillin secreted from the fungal cells in to the
medium .In this phase growth is sharply reduced
 PH is kept constant at 6.5.
 Phenyl acetic acid or pehnoxyacetic acid is fed
continuously as precursor.
 After about 7 days, growth is completed, the pH rises to
8.0 or above and penicillin production ceases.
 The resulting penicillin can be chemically and
enzymatically modified by the introduction of various
acids, amines or amides into the medium in which the
mold is being developed thereby leading to the ultimate
production of a spectrum of biosynthetic penicillins.
Batch-fed fermenter
GKM/ANTIBIOTIC/2013
Tuesday, March 26, 2013
12
Separation and Isolation of
Antibiotics
• In an ideal situation the first isolation process must be
as selective and efficient as possible so as to achieve the
maximum yield, besides to help in subsequent
purification .
• However, the choice of isolation method depends on
particular chemical characteristic feature of an antibiotic
and also their accompanying metabolites .
.
Separation and Isolation of
Antibiotics
• The first step is the recovery process is the removal of
mycelium or cells by filtration or centrifuging.
• Second step is to remove the antibiotic from the spent
production medium by solvent extraction, adsorption or
precipitation.
• Additional solvent extraction, distillation, sublimation,
column chromatography or other methods accomplish
purification.
The various factors that exert vital impact upon the
qualitative and quantitative antibiotic production are :
􀁺 Sources of nutritional C and N
􀁺 Ratio of C/N in nutrients
􀁺 Mineral composition of medium
􀁺 Temperature of incubation
􀁺 Initial pH, control and management of pH during the
entire course of fermentation.
􀁺 Aeration mode and rate
􀁺 Time-phase for addition of special growth and antibiotic
enhancing materials.
Classification of penicillin
I.
Natural Penicillins (best streptococcal and narrow
spectrum)
II. Penicillinase-resistant Penicillins (antistaphylococcal)
III. Aminopenicillins
(improved
Gram-negative:
H.
influenzae, Enterococcus, Shigella, Salmonella)
IV. Extended-spectrum (antipseudomonal) penicillins
V. Beta Lactamase Combinations (expand spectrum to
staph, beta-lactamase producers)
Penicillin G Potassium
Preparation: It is prepared by the interaction of 6-amino-penicillanic acid
and phenyl acetyl chloride in an inert organic solvent.
Uses
1. It is still recommended as an important and useful drug for the
treatment of many Gram-positive organisms, such as streptococci,
pneumococci, gonococci, and meningococci infections.
2. It is mostly destroyed by gastric juice and is, therefore, not given by
oral route, and is best administered as IM or IV injection.
3. The K-salt as such has no advantage over the corresponding Na-salt
except when high doses are used in patients on sodium restriction e.g.,
blood-pressure patients.
4. The K-salt also avoids the incidence of hypokalemic alkalosis which
occasionally takes place during prolonged treatment with high doses of
penicillins.
5. The half-life ranges between 0.5 to 0.7 hour; except 2.5 to 10 hour in
renal failure or after probenecid.
Penicillin V
• Biological Source: It is obtained by the addition of phenoxyacetic
acid to the Penicillium chrysogenum culture
• Uses
• 1. Phenoxymethylpenicillin (Penicillin V) is ‘acid-resistant, due to
the introduction of an electron-withdrawing heteroatom (i.e., Oatom of phenoxy-moiety) into the side-chain.
• 2. It is, therefore, suitable for oral administration.
• 3. It is specifically recommended for respiratory tract infections and
tonsilitis.
Ampicillin and Amoxicillin
Biological Source: orally active, semi-synthetic antibiotics related to
penicillin with side-chain containing a basic amino moiety
uses
• They have an antibacterial spectrum similar to that of penicillin G but
are more effective against gram negative bacilli
• These agents are also widely used in the treatment of respiratory
infections.
• Amoxicillin is found to be more acid stable than ampicillin and
absorption is not affected appreciably by food intake
• Amoxicillin is employed prophylactically by dentists in high-risk
patients for the prevention of bacterial endocarditis
• Ampicillin is the drug of choice for the gram-positive bacillus
Listeria monocytogenes and susceptible enterococcal species.
Cephalosporin
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1.
2.
3.
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In 1948, the first chemical compounds of the cephalosporin group
was isolated from Cephalosporium acremonium.
Today, cephalosporin antibiotics are classified into three manners:
spectrum of activity,
resistance to β- lactamase,
their
activity differences against grampositive/
negative
organisms.
The important difference between penicillin and cephalosporin
structures can be seen in the enlargement from a five- membered to
six- membered ring attached to the common β- lactam core.
The backbone of the cephalosporin is cephem ,which consists of a
bicycle system with a four- membered β- lactam ring and a
hydrocyclothiazide ring.
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Cephalosporins are more stable under acidic conditions and exhibit
fewer allergic reactions; these cephalosporins have a prominent
place in antibiotic therapy in modern times
MOA: Similar to that of the penicillins , interfere with bacterial
peptidoglycan synthesis and subsequently cell wall synthesis .
cephalosporin
Cephalosporin classification
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•
•
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•
First generation Cephalosporins:
Cephalothin , Cephalexin Cefadroxil,
Cephapirin, Cephradine, Cefazolin
Second Generation Cephalosporins:
Cefaclor; Cefamandole; Cefuroxime; Cefonicid
 Third Generation Cephalosphorins:
• Cefotaxime; Cefoperazone ;Ceftazidime;
• Ceftriaxone; Cefmonoxime, Moxalactam;
Prodrugs: Cefpodoxime proxetil; Cefuroxime axetil;
Cephamycins: Cephamycin C; Cefoxitin
Prodrugs
• A major disadvantage of the current cephalosporins is that they are
not rapidly and effectively absorbed through oral route.
• This specific serious drawback is perhaps due to the nature of the
side-chain present at C-3.
• An attempt has been made to design orally active prodrugs, namely:
 cefuroxime-axetil
 cefpodoxime-proxetil,
• which have been developed
by providing an additional ester
group on the C-4 carboxyl moiety.
• Nevertheless, these prodrugs are designed in such a manner that
they are easily hydrolysed to the active agents i.e., drugs by the
esterases.
• Cephamycins represent another group of cephalosporin antibiotics
that are characterized by a 7α-methoxy function, and are usually
produced by two consecutive reactions, namely: hydroxylation and
methylation.
First Generation Cephalosporins
Cefadroxil
• Biological Source It is an orally active semi-synthetic cephalosporin
antibiotic obtained from the species Cephalosporium aeremonium.
• Uses
1. It is intermediate acting and quite effective against Staphylococcus and
certain enteric Gram negative bacilli.
2. Because of its prolonged exeretion criterion, it has an added advantage
of catering for more sustained serum and urine concentrations than are
usually obtained with other oral cephalosporins.
Second Generation Cephalosporins
Cefuroxime
Several antibiotics belonging to the category of ‘second generation
antibiotics’ are absorbed orally.
Interestingly, cefuroxime is available in two different versions
• first—as its sodium salt
• secondly— as its prodrug cefuroxime axetil that are hydrolyzed once
they are absorbed and its absorption rate increased by the intake of food
in-take
Uses
1. Its activity against H. influenzae and ability to penetrate into the CSF
makes it specifically useful for the treatment, control and management of
meningitis caused by this organism.
2. It exhibits an excellent and super activity against all species of gonococci,
hence it is recommended for the treatment of gonorrhea.
3. It may also be employed to treat lower respiratory tract infections normally
caused by H. influenzae and parainfluenzae, Klebsiella species, E. coli, Strep
pneumoniae and pyrogenes and Staph aureus.
4. It is also approved for use against UTIs caused by E. Coli and Klebsiella.
5. It is also recommended for use in bone infections, septicemias and surgical
prophylaxis.
Third Generation Cephalosporins
Cefotaxime
• Biological Source : It is a broad spectrum third generation
cephalosporin antibiotic derived from Cephalosporium acremonium.
• Uses
1.
2.
3.
4.
It is found to be active against a good number of Gram-negative bacilli .
It is highly resistant to the β-lactamases..
It is a recognized and preferred third generation cephalosporin for
Gram-negative meningitis and other serious Gram-negative bacillary
infections outside the CNS.
It is also recommended widely for surgical prophylaxis..