The document details the classification, chemistry, mechanism of action, and pharmacokinetics of antibiotics, focusing on beta-lactam antibiotics such as penicillins and cephalosporins. It includes examples of various antibiotics within these classes, their spectrum of activity, bacterial resistance mechanisms, and clinical uses. Adverse effects, contraindications, drug interactions, and dosing units for penicillins and cephalosporins are also discussed.

1. Antibiosis ( Vuillemin 1889) :
ANTIBIOTICS (Selman Waksman in 1942): any substances
produced by a micro-organism that is antagonistic to the growth of the other
micro-organism in high dilution.

2. 1. Beta-lactam Antibiotics: These antibiotics have a beta-lactam ring
as the essential antibacterial component in their chemical structure.
The antibiotics under this group consist of -
•Penicillins : Examplers are Ampicillin , Amoxycillin, Cloxacillin etc.
Cephalosporins: Examplers are Cephalexin, Cephalothin, Cefachlor,
Cefuroxine, Cefixime, Cefotaxime, Ceftriaxcone Cefepime etc.
Cephamycins: Examplers are Cefmetazole, Cefotetan, Moxalactam
etc.
monobactams : E.g. Aztreonam
carbapenems: E.g. Imipenem
2. Aminoglycosides (Aminocyclitol) Antibiotics:
These are a group of natural and semisynthetic antibiotics which
contain aminosugars in glycosidic linkage. Examples are: -
Streptomycin, Neomycin, Paromomycin, Kanamycin, Tobramycin,
Gentamicin, Amikacin, Sisomicin, Netilmicin.

4. 8. Polyene antibiotic (Antifungal antibiotic): Nystatin, Amphotericin-B
9. Miscellaneous antibiotics: Vancomycin, Tyrothricin, Virginiamycin,
Tiamulin, Novobiocin, Rifamycins etc.
BETA-LACTAM ANTIBIOTICS
• Penicillins, Cephalosporins, Cephamycin, Carbapenems and Monobactams
comes under this group.
PENICILLINS:
• Group of natural and semi-synthetic antibiotics
• Common nucleus :– 6-aminopenicillanic acid (6-APA)
• Share common mode of action.
History:
• Discovered by Sir Alexander Flemming (1928). He discovered that
staphylococal colonies undergo lysis by a mold, penicillium.
• Newer compound are obtained semi-synthetically by chemical manipulations of
6-aminopenicillanic acid.
• Penicillin G – (Penicillium chrysogenum) semi synthetic Penicillins,
Cephalosporins, Cephamycin, Carbapenems and Monobactams come under this
group.

5. Chemistry
• All penicillin contain 5 membered thiazolidine ring (A) connected to a beta-
lactam ring (B) having a secondary amine group (-NH-) to form 6-
aminopenicillanic acid (6-APA).
• Beta – lactam ring is a four membered ring in which amide linkage joins a
carbonyl group and nitrogen.
• A side chain (R) is attached to the beta-lactam ring which determines type of
penicillin.
• Cleavage of beta-lactam ring destroys antibiotic activity; some resistant
bacteria produce beta lactamase (penicillinase) lactam ring.
• 6-APA is responsible for antibacterial activity and its chemical alteration loss
this activity and this determines the type of penicillin group.
• The side chain attached to beta-lactam ring determines the individual penicillin
characteristics.
• The carboxyl group attached to thiazolidine ring is the site of salt formation
(e.g., sodium, potassium and procaine). Conversion to salt ester stabilizes
penicillins and affects solubility and pharmacokinetics.
• Newer compound are obtained semi-synthetically by chemical manipulations of
6-aminopenicillanic acid.

6. FIGURE: CHEMICAL STRUCTURE OF PENICILLIN

7. Properties and Solubility
• Poorly soluble, weak organic acids and are sensitive to heat, light, extremes in
pH, heavy metals, strong alcohols and oxidizing and reducing agents.
• pH 6-6.5 is optimal for stability (range 5.5-7.5)
• A prolonged exposure to water promotes hydrolysis (required reconstitution
with a diluent just before injection).
• Some are rapidly hydrolysed and inactivated by gastric acid and beta-
lactamase and acylase.
• Gastric acid hydrolyses the amide side chain and opens the beta-lactam ring
which is cleaved by beta-lactamase present in some microorganism to produce
penicilloic acid derivatives.
• Aqueous solutions of alkaline sodium salt of sulphonamides also inactivate
penicillins.
• The sodium and potassium salts of natural penicillin enhances water solubility
hence used parentally.
• Trihydrate forms have high water solubility and are administered by both oral
and parenteral routes.

8. Classifications
Penicillins are broadly divided into following groups depending on their spectrum of
antibacterial activity and beta-lactamase sensitivity:
1) Narrow – spectrum penicillins:
I) Narrow-spectrum beta-lactamase sensitive penicillins.
Acid susceptible penicillins/ Natural penicillins e.g., penicillin G.
Acid resistant penicillins/ semisynthetic penicillins e.g., penicillin V and
phenethicillin.
ii) Narrow spectrum beta-lactamase resistant penicillins
a) Isoxazolyl penicillins e.g., cloxacillin, oxacillin, dicloxacillin and flucloxacillin.
b) Non- Isoxazolyl penicillins e.g., methicillin, nafcillin and temocillin
2. Broad spectrum Penicillins
i) Amino penicillins e.g., ampicillin and amoxicillin
ii) Ampicillin Pecursors (aminopenicillins) e.g., hetacillin, bacampicillin, pivampicillin
and talampicillin.
iii) Other e.g., mecillinam
3. Extended-spectrum penicillins/anti-pseudomonal penicillins
i) Carboxypenicillins e.g., carbenicillin, carbenicillin indanyl and ticarcillin
ii) Ureido-penicillins e.g., mezlocillin and azlocillin
iii) Piperazine penicillins e.g., piperacillin
4. Potentiated penicillins/Beta-Lactamase protected penicillin/repository penicillin
e.g., amoxicillin-clavalunic acid (4:1), amipicillin-sulbactum, ticarcillin-
clavulanic acid and piperacillin-tazobactam.

9. Mechanism of Action
• Interfere with the synthesis of bacterial cell wall.
• They produce action by binding to penicillin-binding proteins (PBPs)
• 6-7 PBPs (High molecular weight PBPs - 1A, 1B, 2 and 3 and low molecular
weight PBPs- 4, 5 and 6) have been identified in some bacteria (E.coli).
• The high molecular weights are essential for maintenance of normal cell
morphology and viability that include cell elongation, cell shape, and cell division.
• Inhibition of one of these PBPs by beta-lactam antibiotics produce antibacterial
effects.

10. Factors influencing activity of β-lactam antibiotics
• Most active against rapidly growing and replicating cells
• Efficacy is time dependent (plasma conc. must be maintained above MIC for
long periods)
• Efficacy is more in isotonic environment (isotonic to the host and hypotonic to
the organisms)
• Efficacy is lower in chronic infection (density of bacterial population is more,
slow growth of microorganisms and presence of resistant organisms).
• Do not produce significant post-antibiotic effect.
Antimicrobial Spectrum
• Gram +ve bacteria are more susceptible because their cell wall is located close
to the cell surface and is readily transverse by penicillins.
• Gram –ve are less susceptible because they contain a capsule and outer
lipopolysaccharide membrane surrounding the cell wall that prevents many
penicillins to reach cell wall and target PBPs.
• Inactive for mycobacterium, fungi, protozoa and viruses because they do not
possess cell wall.

11. Bacterial Resistance
• Due to β-lactamase activity produce by certain microorganisms, which
hydrolyse cyclic bond of β-lactam ring.
• Due to decreased permeability of drug due to which the drug did not reach
target PBPs.
• Loss or alteration of aqueous channels (porins) in the outer membrane of Gram
–ve bacteria also results in resistant to penicillins.
• Active efflux of antibiotics through cell membrane poses resistancy.
• Altered PBPs, which results in lower affinity for β-lactam antibiotics, requiring
high concentrations to affect binding and inhibition of cell wall synthesis.
• Quiescent organisms (persisters): In any bacterial population, a few organisms
do not grow and remain unaffected by the penicillin.
• Tolerant organisms: The growth of some organisms are inhibited but do not
undergo lysis at usual concentrations.

12. Pharmacokinetics
• Absorption
• Penicillins are weak acids, which favour oral absorption.
• But some are destroyed by gastric acid and, thus, cannot be given
orally.
• Peak plasma concentration : Oral – 2 hrs; IM/SC – 15-30 minutes
• Absorption is slow and prolonged for depot preparations (procaine
penicillin G and benzathine penicillin G)
• Oral absorption of some penicillin is decreased by food.
• Distribution
• Widely distributed throughout the body.
• Do not penetrate into some sites (brain, bone, cartilages, cornea, CSF
and bronchial secretions) unless these sites are inflamed.
• They do not penetrate living phagocytic cells to a significant extent.
• Plasma protein binding is 20-80%.

13. • Metabolism
• No significant biotransformation and are excreted unchanged.
• In impaired renal function, some may undergo biotransformation e.g.,
aminopenicillin and penicillin G.
The metabolites formed is penicilloic acid derivative which tend to be allergic.
• Excretion
• Excreted rapidly in urine: Glomerular filtration – 20%; Tubular secretion
- 80%
• Biliary route excretion also occur for broad-spectrum semi-synthetic.
• Also excreted through milk.
• Elimination half-lives of most penicillins vary between 30-120 minutes.

14. CLINICAL USES:
Sl.No. Name of Drugs Indications
1 Penicillin G Systemic and Local infections in all species such as mastitis, pyelonephritis, lumpy
jaw in cattle, swine erysipelas, tetanus, anthrax and vibrosis.
2 Repository Penicillin Cattle: Calf scours, enteritis, pneumonia, salmonella septicaemia, foot rot, E.coli
mastitis, metritis and pyelonephritis
Sheep: Foot rot, abscesses, metritis and pneumonia
Horses: Enteritis, metritis and respiratory infections
Dogs & Cats: Dermatitis, enteritis, respiratory and UTI infections
Poultry: Enteritis.
3. Extended spectrum
Penicillins
Ampicillin is recommended against Streptococcus faecalis, H. influenzae and some
E.coli, Klebsiella and Proteus strain. Amoxicillin is similar to ampicillin in
spectrum but better absorbed orally and is sometimes used in combibation
with clavulanic acid. Azlocillin is used against Pseudomonas and Proteus
spp.

15. Adverse Effects/Side Effects
Hypersensitivity
• Due to metabolites, penicilloic acid, which react with proteins and serve as
haptan to cause an immune reaction ranging from maculopapular rash to
angio neurotic oedema.
• In cattle, rash, urticaria, drug fever, angioedema, serum sickness,
vasculitis, and rarely anaphylaxis are the symptoms.
GI disturbances
• Use of broad spectrum may produce GI disturbances, particularly diarrhea
and superinfection due to disruption of normal GI microflora.
Platelet dysfunction
• Some produce thrombocytopenia and decrease agglutination in patient
predisposed to haemorrhages or those receiving anticoagulant therapy.
Organ toxicity
• They are irritating to neuronal tissues and can provoke seizures when
administered in high dose or when injected intrathecally.
Cation toxicity
• Cation toxicity are possible as Penicillins are administered as sodium or
potassium salt.
• Sodium excess may aggrevate the Congestive Heat Failure.
• Rapid IV administration of potassium salt may produce hyperkalaemia.
Superinfections
• With broad/extended spectrum penicillins.

16. Contraindication/Precaution
• Hypersensitive patient
• Sodium or Potassium salt may be avoided in pre-existing electrolyte
abnormality, renal disease and CHF.
• Oral route is slow and impaired absorption. Hence, not recommended for
septicaemia.
• Not teratogenic, but avoid in pregnancy as it crosses placenta.
Drug Interaction
• Salicylates, phenylbutazone and sulfonamides displaces penicillins from PBPs
when administered concurrently.
• With aminoglycosides – synergistic or additive effect. But not carbenicillin and
ticarcillin (interaction).
• With probenicid and other weak organic acid competitively block tubular
secretion of most penicillin, thereby increase penicillin concentration in blood
and plasma half-lives.
• Antagonist with bacteriostatic drugs.
• With anticoagulant, severe bleeding may occur.
• Acid – susceptible penicillins (Penicillin G) and normal saline or other acidic
pH fluids should not be mixed. They inactivates penicillin.

17. Unit of Penicillin
• The International Unit of penicillin is the amount of activity present in 0.6 µg of
the crystalline sodium salt of penicillin G. Thus,
• 1 mg of pure penicillin G sodium equals to 1667 Unit.
• 1 mg of pure penicillin G potassium equals to 1595 Unit.
• 1 mg of pure penicillin G procaine equals to 1050 Unit.
• 1 mg of pure penicillin G benzathine equals to 1272 Unit.
• 1 mg of penicillin V equals to 1380 – 1610 Unit.

18. Table: Recommended doses for Penicillins

19. CEPHALOSPORINS
Cephalosporins are semi-synthetic antibiotics obtained by making different
substitutions in 7-aminocephalosporanic acid of cephalosporin-C obtained from
a fungus Cephalospoium acremonium
Natural cephalosporins viz., cephalosporins P,N and C are obtained from
Cephalosporium acremonium.
CHEMISTRY
Basic structure – Dihydrothiazine ring fused to a beta lactam ring having
secondary amine to form 7-aminocephalosporanic acid (the nucleus)
• By addition of different side chains to position 7 of the β-lactam ring (R1) and
position 3 of dyhydrothiazine ring (R2), semisynthetic cephalosporins are
produced.
• Modification at position 7 alter the spectrum of antibacterial activity.
• Substitution at position 3 of the nucleus cause changes in pharmacokinetic
properties.
Properties and solubility:
• Physical and chemical properties same with penicillin except few.
• More water soluble and acid stable than penicillin.
• More stable temperature and pH changes
• They have vary susceptibility to β-lactamase (cephalosporinase) which may
or may not attack penicillin.

20. FIGURE: CHEMICAL STRUCTURES OF BETA LACTAM ANTIBIOTICS
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21. Classification: Based on chronology of development.
• First generation:
Oral : cephalexin, cefadroxil, cephradine
Parenteral: cephalothin, cefazolin, cephalexin,cephaloridine
cephalonium.
Intramammary: cephapirin, cephaloridine (nephrotoxic), cefacetrile.
• Second generation:
Oral : cefaclor, cefuroxime
Parenteral: cefamandole (MTT), cefonicid, ceforanide, cefotetan(MTT)
Intramammary: cefuroxime
• Third generation
Oral: cefixime
Parenteral: cefotaxime, ceftiofur (longest plasma half-lives: 9-12h), ceftriaxone,
cefoperazone (MTT), Moxalactam (MTT), ceftizoxime, ceftazidime, ceftibuten,
cefsulodin.
Intramammary: cefoperazone
• Fourth generation e.g., cefepime, cefpirome and cefquinome

22. Mechanism of Action:
• Bactericidal
• Inhibit Bacterial Cell wall synthesis in a manner similar to penicillin.
• But, binds to different proteins.
• More active against actively growing bacteria.
Antibacterial Spectrum:
• First generations: G –ve= ++ , G +ve =+++, less antianaerobic, less
resistant to betalectamase.
• Second generation: G –ve=+++ , G +ve = +++, more antianaerobic,
relatively resistant to betalectamase.
• Third generation: G+ve= ++, G –ve= +++, Also active for Pseudomonas
aeroginosa.
• Fourth generation: Resistant to β-lactamase. Broad spectrum including
Pseudomonas aeroginosa.
Bacterial Resistance: Same as penicillin

23. Pharmacokinetics
Absorption:
• Only few are acid stable and are given orally. Others are given IM or IV.
• Orally given are well absorbed with bioavailabilty of 75-90 %.
• Absorption from IM is rapid and reached peak plasma conc. within 30 minutes.
Distribution:
• Widely distributed in body tissues and fluids including lungs, kidneys, bone,
placenta, soft tissues and pleural, pericardial and joint fluids.
• Third generation cross BBB and are drug of choice for meningitis due to G-ve
bacteria.
• Poor penetration into prostatic tissues and viteous humours.
• Enter milk in low concentration
• Plasma protein binding is variable 20-80 % (species specific).
Biotransformation:
• Most do not undergo biotransformation and excreted unchanged.
• Some are deacetylated in liver and other tissues and excreted inactive or mildly
active (e.g., cefotaxime, cefalothin)
Excretion:
• Mainly by kidneys via tubular secretion (mainly) and glomerular filtration.
• Third generation- through bile.
• Plasma half-lives 30-120, third generation have longer half lives.
• Maintain effective blood levels for 6-8 hrs.
• Like penicillin, probenecid increase its half lives.

24. Side effects/adverse effects:
• More or less similar with penicillin.
• Relatively non toxic.
• Allergy (10-20% of patients with penicillin allergy are also allergic to
cephalosporins.
• Nephritis and acute renal failure.
• Superinfections
• GI upsets when given orally.
• Some cephalosporins ( cefoperazone, cefamandole, and moxalactam)may
produce coagulopathies
Clinical indications:
• Septicemia (cefuroxime, cefotaxime i.v.)
• Pneumoniae due to suscetible organisms
• Meningitis (ceftriaxone, cefotaxime i.v.)
• Urinary Tract Infection (especially in pregnancy or in patienrs unresponsive to
other drugs)
• Sinusitis (cefadroxil orally)
• Mastitis

25. Table: Recommended doses for cephalosporins

26. Table: Pharmacokinetic profile of selected cephalosporins

27.  1. Cephamycin: These are closely related with cephalosporins, but have
a methoxy group at position 7 of beta lactam ring of 7-ACPA.
 A. Cefmetazole
 B. Cefotetan
 C. Cefoxitin- Streptomyces lactamdurans, Similar to properties of 2nd
gen.
CPs
 D. Moxalactam: similar to 3rd
gen. CPs
 2. Monobactam:
 A. Aztreonam: Chromobacterium violaceum
 3. Carbapenems:
 A. Imipenem: semisynthetic from thienamycin: S. Catleya. Combined with
Cilastatin (inhibitor of ranal tubular dihydropeptidase)
 B. Meropenam, C. Faropenam

28.  Peptidoglycan constitutes the cell wall of bacteria, but not eukaryotes.
 It is the equivalent of non-stretchable string bag enclosing the whole
bacterium.
 For G-ve, the bag consist of a single thickness.
 For G+ve, it is upto 40 layers thick.
 Each layers consists of multiple backbones of amino sugars – alternating
N-acetylglucosamine (NAG) and N-acetylmuramic cid (NAMA) residues.
 NAMA has short peptide side chain which are cross-linked to form a
latticework which is differ in different species (staphylococci – five
glycine).
 Cross-linked is responsible for the strength that allows the cell wall to
resist the high internal osmotic pressure.

29. Fig. Schematic diagram of a sinlge layer of peptidoglycan from a bacterial cell
showing the site of action of the β-lactam antibiotics

31.  NAMA attached to UDP and a pentapeptide is transferred to the C55 lipid
carrier in the membrane, with the release of UMP.
 UDP-N-acetylglucosamine react together and form disaccharide carrying the
pentapeptide and attached to the carrier. (Disaccharide with peptide
attached is the basic building block of the peptidoglycan).
 Five glycine residues are attached to the peptide chain at this stage.
 The building block is then transported to the outside of the cell and added to
the growing end of the peptidoglycan, the ‘acceptor’, with the release of the
C55 lipid, which still has two phosphate attached.
 The lipid then lost one phosphate group and thus becomes available for
another cycle.
 Cross-linking between the peptide side-chains of the sugar residues in the
layer then occur.

32. Cycloserine: Structural analog of D-alanine and competitively inhibits cell wall
synthesis by preventing the formation of D-alanine and of D-ala-D-ala dipeptide
which is added to the initial tripeptide side-chain on N-acetyl muramic acid.
Vancomycin: Inhibits the release of building block unit from the carrier, thus
preventing its addition to the grwoing end of the peptidoglycan.
Bacitracin: Interfere with the regeneration of the lipid carrier by blocking its
dephosphorylation.
β-lactam: These antibiotics inhibit the final transpeptidation that establishes the
cross-links by forming covalent bonds with PBP that have transpeptidase and
carboxypeptidase activities.