文档介绍：Chapter 42
Beta-Lactam Antibiotics
β-内酰胺类抗生素
Pharmacology
Instructor : Lei Linsheng 雷林生
β-lactam antibiotics are frequently prescribed drugs.
They share mon basic structure- β-lactam ring.
All β-lactam antibiotics have the same bactericidal mechanism of action. They block a critical step in bacterial cell wall synthesis.
CLASSIFICATION
of β-lactam antibiotics
Ⅰ. Penicillins
Ⅱ. Cephalosporins
Ⅲ.Other β-lactam drugs
化学结构
6-APA
7-ACA
1. Chemistry
Basic Structure
Ⅰ. PENICILLINS 青霉素类
A thiazolidine噻唑烷- ring (A) is attached to a β-lactam ring (B) ;
β-lactam ring carries a secondary amino group (RNH - );
Substituents can be attached to the amino group.
2. Classification of Penicillins
A. Natural Penicillins (eg, penicillin G)
B. Semisynthetic Penicillins
Orally effective (penicillin V)
Penicillinase-Resistant ( al penicillins, oxacillin)
Broad-Spectrum (eg. ampicillin )
Antipseudomonal penicillins (Extended-spectrum, piperacillin)
Gram-negative bacteria susceptible penicillins (mecillinam)
(1) Penicillins inhibit bacterial growth by interfering with a specific step in bacterial cell wall synthesis.
Penicillins are structural analogs of the natural D-Ala-D-Ala substrate and they are covalently bound by PBPs (penicillin binding proteins, transpeptidases) at the active site. After Penicillin has attached to the PBPs, the transpeptidation reaction is inhibited and the cell wall is induced to break down.
3. Mechanism of action
transpeptidase
M: N-acetylmuramic acid. G: N-acetylglucosamine.
(2) Penicillins also induce and enhance the activity of the autolytic enzymes (autolysin), resulting in lysis of anism in an isotonic environment.
Mechanism of action