This document summarizes the salient features of β-lactam antibiotics and their mode of action, classification, spectrum of activity, and common adverse effects. It discusses penicillins, cephalosporins, and their subclasses. Penicillins inhibit bacterial cell wall synthesis by binding to penicillin binding proteins. They are more active against gram-positive bacteria. Cephalosporins have a similar mode of action but their activity spectrum varies between generations from gram-positive to broad-spectrum. Common adverse effects for both classes include hypersensitivity reactions and dysbiosis.

1. SALIENT FEATURES OF β-LACTAM ANTIBIOTICS
DRUG
CATEGORY
MODE OF
ACTION
CLASSIFICATION AND
EXAMPLES
SPECTRUM OF ACTIVITY
COMMON ADVERSE
EFFECTS
Penicillins
(Bactericidal)
Their basic structure
consists of a β-lactam
ring fused to a
thiazolidine ring.
They are more active
against gram positive
bacteria than gram
negative (due to
protection of cell
wall by means of
capsule and outer
membrane).
They are inactive
against
Mycobacteria, fungi,
protozoa and viruses.
β-lactam
antibiotics
produce their
anti-bacterial
effects by
binding to a
family of
proteins called
penicillin
binding
proteins
(PBPS).
Inhibition of
one or more of
these PBPS by
β-lactams leads
to the
inhibition of
bacterial cell
wall synthesis.
The blockage
of cell wall
synthesis is
also thought to
activate the
enzymes
known as
autolysins that
degrade the
abnormally
formed
peptidoglycan.
Beta-lactamase sensitive, acid sensitive
Penicillin G (Natural Penicillin)
Narrow spectrum: Effective only against gram
positive bacteria. Susceptible to β-lactamase
induced break down.
1. Hypersensitivity reactions:
Rashes, angio-edema, urticaria,
vasculitis, serum sickness,
anaphylaxis.
2. Cation toxicity:
Hypernatremia aggravates the
CHF.
3. Dysbiosis: Disruption of
normal microflora from rumen/GI
tract leads to indigestion, diarrhea
and superinfection.
4. Neurotoxicity: Administration
of high doses, prolonged
administration or intra-thecal
administration can provoke
seizures and ataxia. Epileptic
patients are at high risk.
Beta-lactamase sensitive, acid resistant
Penicillin V
(Semi-synthetic Penicillin)
Beta-lactamase resistant Penicillins:
Methicillin, Oxacillin, Cloxacillin
Aminopenicillins:
Amoxycillin, Ampicillin
Broad spectrum: Effective against gram positive
and gram negative bacteria excluding
Pseudomonas. Susceptible to β-lactamase induced
break down.
Antipseudomonal Penicillins:
Piperacillin
Extended spectrum: Effective against gram
positive and gram negative bacteria including
Pseudomonas. Susceptible to β-lactamase induced
break down.
Beta-lactamase protected Penicillins:
Amoxycillin + Clavulinic acid
(Co-amoxy clav------augmenton@),
Ampicillin+ Sulbactam
Piperacillin +Tazobactam
Potentiated spectrum: Resistant to β-lactamase
induced break down. They possess re-established
antibacterial action against Staphylococcus aureus
(except MRSA), Salmonella, E. coli, Shigella,
Proteus and Klebsiella.
Cephalosporins
(Bactericidal)
Their basic structure
consists of a β-lactam
ring fused to a
dihydrothiazine ring.
1st
Generation Cephalosporins:
Cephradine, Cephalothine
Stronger activity against gram positive bacteria and
weaker activity against gram negative bacteria. 1. Hypersensitivity reactions:
Rashes, fever, eosinphilia,
lympadenpathy and anaphylaxis.
2. Dysbiosis: Disruption of
normal microflora from rumen/GI
tract leads to indigestion, diarrhea
and superinfection.
3. Nephrotoxicity
2nd
Generation Cephalosporins:
Cefaclor, Cefuroxime
Stronger activity against gram negative bacteria but
weaker activity against gram positive bacteria.
3rd
Generation Cephalosporins:
Ceftiofur, Cefotaxime
More active against gram negative (especially
enteric) bacteria while less active against gram
positive cocci.
4th Generation Cephalosporins:
Cefpirome, Cefquinome
Active against gram positive cocci, gram negative
bacilli and Pseudomonas.

2. SALIENT FEATURES OF ANTIMICROBIAL DRUGS (INHIBITORS OF BACTERIAL PROTEIN SYNTHESIS)
DRUG
CATEGORY
MODE OF ACTION CLASSIFICATION AND EXAMPLES SPECTRUM OF ACTIVITY
COMMON ADVERSE
EFFECTS
Aminoglycosides
(Bactericidal)
They bind to 30S ribosomal subunit and
impair the bacterial protein synthesis
through several mechanisms including:
(a) Interference with the formation of
initiation complex. (b) Distortion of
mRNA condons resulting in misreading
of the codons. (c) Premature termination
of translation.
1. Narrow spectrum: Effective only against gram
negative bacteria.
Streptomycin
Dihydrostreptomycin
1. Nephrotoxicity
2. Ototoxicity
3. Neuromuscular blockade
2. Broad spectrum: Effective against gram
negative and gram positive bacteria excluding
Pseudomonas.
Neomycin
Kanamycin
3. Extended spectrum: Effective against gram
negative and gram positive bacteria including
Pseudomonas.
Gentamicin
Tobramycin
Tetracyclines
(Bacteriostatic)
They bind to 30S-ribosomal subunit and
prevent binding/ access of amino-acyl
tRNA to the acceptor (A) site on the
mRNA-ribosome complex. This
prevents addition of amino acids to the
growing peptide chain resulting in
inhibition of protein synthesis.
Broad spectrum: They are are active against a
wide range of aerobic and anerobic gram positive
and gram negative bacteria, rickettisiae and
spirocheates. They are inactive against fungi and
viruses.
Short acting tetracyclines
(t1/2 < 8 hours)
Oxytetracycline, Chlortetracycline
1. Hypoplasticity of bones and
teeth, permanent dental
discoloration, impairment of
normal neonatal osteogenesis and
odontogenesis
2. Hepatotoxicity
(Fatty liver infiltration)
3.GIT problems: diarrhea if give orally
4. CVS problem: hypotension,
collapse and sudden death due to
chelation with blood ca+2(fast IV)
Intermediate acting tetracyclines
(t1/2 8-16 hours)
Methacycline,
Long acting tetracyclines
(t1/2 >16 hours)
Doxycycline, Minocycline
Amphenicols
(Bacteriostatic)
They reversibly bind to 50S-ribosomal
subunit and prevent the action of
peptidyl transferase enzyme.
Broad spectrum: They are active against many
gram positive and gram negative bacteria
(including both aerobes and anaerobes), rickettsiae
and Mycoplasma but have no or less activity
against many strains of Pseudomonas and Proteus.
They are inactive against Mycobacteria, fungi,
protozoa and viruses.
Chloramphenicol
Thiamphenicol
Florfenicol
1. Mylo-suppression
2. Malabsorption syndrome
3. Gray-baby syndrome
Macrolides
(Bacteriostatic)
Macrolides bind to 50S-ribosomal
subunit and block the translocation step
of bacterial protein synthesis.
Macrolides are effective against most aerobic and
anerobic gram positive bacteria but not gram
negative bacteria (except Pasteurella and
Haemophilus), Mycoplasma, Mycobacterium,
Chlamydia and Rickettsiae. Most members of
enterobacteriaceae are resistant to them. They are
inactive against fungi, protozoa and viruses.
Erythromycin
Tylosin
Tilmicosin
Clarithromycin
Azithromycin
Oleandomycin
1. GI disturbances:
Diarrhea, regurgitation and
epigastric pain.
2. Hypersensitivity:
Rashes, fever, skin eruptions.
Lincosamides
(Bacteriostatic)
They reversibly bind to 50S-ribosomal
subunit and interfere with bacterial
protein synthesis.
These are more effective against gram positive
anaerobes, less active against gram positive
aerobes and ineffective against gram negative
bacteria.
Lincomycin
Clindamycin
Pirlimycin
1. Pseudomembranous colitis
2. Ketosis

3. SALIENT FEATURES OF ANTIMICROBIAL DRUGS (QUINOLONES AND SULPHONAMIDES)
DRUG
CATEG
ORY
MODE OF ACTION CLASSIFICATION/EXAMPLES
SPECTRUM OF ACTIVITY TYPE OF
ACTIVITY
COMMON
ADVERSE EFFECTS
Quinolo
nes
They inhibit the action of
DNA-gyrase enzyme that
is responsible for the
supercoiling of DNA.
Reduction in supercoiling
occurs with subsequent
disruption of bacterial
DNA replication.
Extended gram negative spectrum
1st
Generation quinolones
(Non-fluorinated quinolones):
(Nalidixic acid, Oxolinic acid,
Pipemidic acid)
Bactericidal
1. Chondrodestruction
(cartilage deformities
and joint growth
disorders due to
chelation of Mg++
in
cartilages)
2. Convulsions
3. Crystalluria (due to
their low solubility in
acidic urine)
Broad spectrum: Active against a wide range of
gram positive and gram negative bacteria
(excluding streptococcus and anaerobes),
mycoplasma and chlamydia
2nd
Generation quinolones
(1st
Generation fluoroquinolones):
(Ofloxacin, Norfloxacin, Enrofloxacin,
Ciprofloxacin, Flumequine)
Broad spectrum:
Also cover anaerobes and gram positive cocci
2nd
Generation fluoroquinolones:
(Gatifloxacin, Levofloxacin)
Sulphon
amides
They act as PABA
analogues and inhibit the
bacterial folic acid (which
is further utilized for the
synthesis of purines,
methionine, thymidine
and glycine that are vital
for bacterial growth and
multiplication) synthesis
by competitively blocking
the action of
dihydropteroate synthase
enzyme.
Locally acting Sulphonamides
1. Topically acting Sulphonamides
(Sulphacetamide)
2. Gut active Sulphonamides (Sulphaguinidine) 1. Susceptible micro-organisms:
a. Gram positive bacteria
(Streptococcus, Bacillus, Hemophilus,
Actinobacillus)
b. Gram negative bacteria
(Enteric bacteria)
c. Protozoa (Plasmodium, Eimeria,
Toxoplasma)
2. Resistant micro-organisms:
Leptospira, Mycoplasma, Pseudomonas,
Spirocheates, Rickettsiae and acid-fast
bacteria
Bacteriostatic
1. Crystalluria
2. Idiosyncratic
hemolytic anemia
3. Keratoconjuctivitis
sicca
4.Hypoprothrombinemi
a
5. Hypersensitivity
reactions
(expoliative dermatitis,
immune-mediated
polyarthritis)
Systemically acting Sulphonamides
1. Short acting [Duration < 12 hours]
(Sulphanilamide, Sulphadiazine)
2. Intermediate acting [Duration 12-24 hours]
(Sulphadimidine, Sulphamethoxazole)
3. Long acting [Duration 24-48 hours]
(Sulphaethoxypyridazine,
Sulphamethoxypyridazine)
4.Ultra long acting [Duration > 48 hours]
(Sulphadoxine)
Potentiated Sulphonamides
Co-trimoxazole (Trimethoprim +
Sulphamethoxazole)
Co-trimazine (Trimethoprim + Sulphadiazine)
Pyrimethamine + Sulphadoxine
Bactericidal

4. SPECTRUM OF ACTIVITY OF COMMON ANTI-MICROBIAL DRUGS
CLASS OF MICRO-ORGANISMS
DRUG CATEGORY BACTERIA MYCOPLASMA CHLAMYDIA PROTOZOA RICKETTSIA FUNGI
SULPHONAMIDES + + + + + _
FLUROQUINOLONES + + + _ + _
AMPHENICOLS + + + _ + _
TETRACYCLINES + + + +/- _ _
MACROLIDES + + + +/- _ _
LINCOSAMIDES + + _ +/- _ _
AMINOGLYCOSIDES + + _ _ _ _
DI-AMINOPYRIMIDINES + _ _ + _ _
BETA-LACTAMS + _ _ _ _ _