This document summarizes β-lactam antibiotics, specifically penicillins. It discusses their mechanism of action by inhibiting bacterial cell wall synthesis through binding to penicillin binding proteins. It classifies penicillins as narrow or extended spectrum based on their antimicrobial range. Narrow spectrum penicillins like penicillin G are effective against gram positive and some gram negative bacteria. Extended spectrum penicillins have broader coverage against gram negatives. The document also covers the pharmacokinetics and clinical uses of different penicillins.

1. Content
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β-Lactam antibiotics
• Penicillins
– Mechanism of action
– Classification
– Pharmacokinetics
– Clinical uses

2. β-Lactam antibiotics
• All of the drugs in this group contain a β-lactam ring in their
structure
• Inhibit bacterial cell wall synthesis
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3. 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
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4. Penicillin
• 6- amino pencillanic acid (6-APA)- active moiety
• Has intact β-lactam ring and amino group at C-6 joined at
thiazolidine ring
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5. Mechanism of action
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• Inhibits bacterial cell wall synthesis
• Bacterial cell wall is composed of peptidoglycan
• Peptide chains are cross linked by pentaglycine bridge

6. Mechanism of action
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• 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

7. Resistance to penicillin
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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

8. Classification of Penicillins
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• 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

9. Narrow spectrum penicillin
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10. Extendend spectrum penicillin
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11. Pharmacokinetics
Narrow spectrum penicillin
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• 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

12. Antimicrobial spectrum
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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

13. Pharmacokinetics
Extended spectrum penicillin
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• β-lactamase sensitive
• Aminopenicillin – acid stable
• Carboxypenicillin and Ureidopenicillin – acid labile
• Good bioavailability
• Excreted through kidneys

14. Antimicrobial spectrum
Extended spectrum penicillin
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• 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

15. Clinical uses
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• UTIs, typhoid fever, bacillary dysentry
• Amoxycillin – for eradicating H.pylori in duodenal and gastric
ulcers
• Ampicillin – for meningitis by Listeria monocytogenes
• Endocarditis
• Septicemia
• Cellulitis