、CHg C-NH-CH-CH 1 Site of action of penicillinase 2 Site of action of amidase O=CN—CHC0OH A Thiazolidine ring Penicillins B B-Lactam ring Penicillinase Amidase RCH+NH2-CH-CH CHa O=CN一CHC00H O=C N-CH-COOH OH H R 6-Aminopenicillanic Acid Penicilloic Acids Fig 32-1 Chemical structure of penicillins
Fig 32-1 Chemical structure of penicillins
【Mechanism of action】 1.Penicillins inhibit the formation of cell walls Penicillins exerts its effect by binding to cellular receptors (Penicillin-binding proteins,PBPs, transpeptidation enzymes)>inhibiting transpeptidation reactions->interrupt the synthesis of cell wall peptidoglycan. 2.Penicillins also remove or inactivate an inhibitor of lytic enzymes (autolysin),resulting in lysis of microorganisms in an isotonic environment
【Mechanism of action】 1.Penicillins inhibit the formation of cell walls ： Penicillins exerts its effect by binding to cellular receptors （Penicillin-binding proteins,PBPs, transpeptidation enzymes） → inhibiting transpeptidation reactions → interrupt the synthesis of cell wall peptidoglycan. 2.Penicillins also remove or inactivate an inhibitor of lytic enzymes (autolysin), resulting in lysis of microorganisms in an isotonic environment
3 .In general,penicillin G is more effective against Gram-positive organisms than semi- synthetic penicillins. 【Pharmacokinetics penicillin G is rapidly destroyed at pH of gastric secretion. Penicillin G is widely distributed throughout the body,but dose not easily pass across the blood- brain barrier
３.In general, penicillin G is more effective against Gram-positive organisms than semisynthetic penicillins. 【Pharmacokinetics】 penicillin G is rapidly destroyed at pH of gastric secretion. Penicillin G is widely distributed throughout the body, but dose not easily pass across the bloodbrain barrier
Penicillin G is metabolized slightly by the liver and mainly is excreted by the kidney.Probenecid blocks the active tubular secretion of penicillin G and hence prolongs its action. long-acting forms such as penicillin G procaine and penicillin G benzathine are available for specific purposes. Semi-synthetic penicillins usually are absorbed more easily than penicillin G orally and they are excreted by both kidney and bile. Half-life of penicillin G is about 30 min,and much shorter than that of semi-synthetic penicillins
• Penicillin G is metabolized slightly by the liver and mainly is excreted by the kidney. Probenecid blocks the active tubular secretion of penicillin G and hence prolongs its action. • long-acting forms such as penicillin G procaine and penicillin G benzathine are available for specific purposes. • Semi-synthetic penicillins usually are absorbed more easily than penicillin G orally and they are excreted by both kidney and bile. • Half-life of penicillin G is about 30 min, and much shorter than that of semi-synthetic penicillins
[Antimicrobial activity and clinical use of penicillin G) These have the greatest activity against gram- positive organisms,gram-negative cocci,and non-B-lactamase-producing anaerobes. However,they have little activity against gram- negative rods.D They are susceptible to hydrolysis by B lactamases. Penicillin G may be used actively and prophylactically in the following cases:
【Antimicrobial activity and clinical use of penicillin G】 These have the greatest activity against grampositive organisms, gram-negative cocci, and non-β-lactamase-producing anaerobes. However, they have little activity against gramnegative rods. They are susceptible to hydrolysis by β lactamases. Penicillin G may be used actively and prophylactically in the following cases：