Penicillins

Penicillins

Content

β-Lactam
antibiotics

       Penicillins

      Mechanism
of action

      Classification

      Pharmacokinetics

      Clinical
uses 

Objectives

At the end of this session, students will be able to:

       Classify
Penicillins

       Describe
the mechanism of action of Penicillins

       Outline
the pharmacokinetic profile of Penicillin

       Discuss  the clinical uses of Penicillins

β-Lactam
antibiotics

       All of the drugs in this group
contain a β-lactam ring in their structure

       Inhibit
bacterial cell wall synthesis

Penicillin

       Obtained
from Penicillium notatum

       At
present obtained from Penicillium chrysogenum

       Consists
of sulfur containing thiazolidine ring fused with β-lactam ring having a side chain at C-6

       6-
amino pencillanic acid (6-APA)- active moiety

       Has
intact β-lactam ring and
amino group at C-6 joined at thiazolidine ring

Mechanism of action

 

       Inhibits
bacterial cell wall synthesis

       Bacterial
cell wall is composed of peptidoglycan

       Peptide
chains are cross linked by pentaglycine bridge

       Process
of trans bridging –  transpeptidation

       Catalysed
by penicillin binding protein (PBP)

       Penicillin
competes and inhibits PBPs

       Forms
imperfect cell wall

       Osmatic
drive of fluid

       Bacetrial
death by swelling and lysis

       Bactericidal
action

Resistance to penicillin

By any of the following mechanism

       Inactivation
of β-lactam ring by β-lactamase

       Modification
of PBPs

       Reduction
in penicillin permeability to reach PBPs

       Activation
of antibiotic efflux mechanism

Classification of Penicillins

       Based
on antimicrobial spectrum

       Some
are stable to gastric acid

       Some
are acid labile (give parenterally)

       Some
are resistant to β-lactamase

       Others
are β-lactamase sensitive

Narrow spectrum penicillin

Extendend spectrum penicillin

Pharmacokinetics
Narrow spectrum penicillin

       Penicillin
V and G- natural penicillin

       β-lactamase sensitive

       Penicillin
G – acid labile

       Easily
absorbed

       Wide
distribution – except eye, prostrate and CNS

       Excreted
through kidneys

Extended spectrum penicillin

       β-lactamase sensitive

       Aminopenicillin
– acid stable

       Carboxypenicillin  and Ureidopenicillin – acid labile

       Good
bioavailability

       Excreted
through kidneys

Antimicrobial spectrum

Narrow spectrum penicillin

       Penicillin
G and V – Effective against gram positive and gram negative bacteria

       Semisynthetic
– Cloxacillin, dicloxacillin, methicillin and nafcillin

       Spectrum
of action similar to natural penicillin

Extended spectrum penicillin

       Retains
antimicrobial spectrum of penicillin G

       Extended
spectrum against gram negative organism

       Amoxycillin
– for eradicating H.pylori in duodenal and gastric ulcers

       Piperacillin-
antipseudomonal penicillin

Clinical uses

       UTIs,
typhoid fever, bacillary dysentry

       Amoxycillin
– for eradicating H.pylori in duodenal and gastric ulcers

       Ampicillin
– for meningitis by Listeria monocytogenes

       Endocarditis

       Septicemia

       Cellulitis

Summary

       β-lactam antibiotics are the group
of drugs that contain a β-lactam ring in their structure and they act by i
nhibiting
bacterial cell wall synthesis

       They
include – penicillins, cephalosporins, monobactams and cabapenems

       Penicillins
are the drug initially obtained from fungus, now obtained by semisynthetic
process

       They
used in the treatment of UTIs, endocarditis, septicemia

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