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PENICILLINS The penicillins share a common chemical nucleus (6-aminopenicillanic acid) that conta... more PENICILLINS The penicillins share a common chemical nucleus (6-aminopenicillanic acid) that contains a beta-lactam ring essential to their biologic activity. Antimicrobial Action & Resistance The initial step in penicillin action is the binding of the medication to receptors, called penicillin-binding proteins. Aer penicillins attach to receptors, peptidoglycan synthesis is inhibited due to blockage of transpeptidation. The final bactericidal action is to remove an autolytic enzyme inhibitor in the cell wall, which results in cell lysis. Organisms that produce beta-lactamases (penicillinases) are resistant to some penicillins because the beta-lactam ring is broken. Only organisms actively synthesizing peptidoglycan (in the process of multiplication) are susceptible to penicillins and other beta-lactam antibiotics. Nonmultiplying organisms or those lacking cell walls are not susceptible. Microbial resistance to penicillins is associated with five mechanisms: (1) production of beta-lactamases, (eg, by staphylococci, gonococci, Haemophilus species, and coliform organisms, including extended-spectrum beta-lactamase (ESBL)-producing bacteria); (2) lack of penicillin-binding proteins or decreased ainity of penicillin-binding protein for beta-lactam antibiotic receptors (eg, resistant pneumococci, methicillin-resistant staphylococci, enterococci); (3) impermeability of the cell envelope (eg, by Pseudomonas species); (4) failure to activate autolytic enzymes in the cell wall-"tolerance," (eg, in staphylococci, group B streptococci); and (5) cell wall-deficient (L) forms or mycoplasmas, which do not synthesize peptidoglycans. 1. Natural Penicillins The natural penicillins include penicillin G for parenteral administration (aqueous crystalline for intravenous or benzathine penicillin G for intramuscular administration) or for oral administration (penicillin G and phenoxymethyl penicillin [penicillin V]). They are most active against gram-positive organisms and are susceptible to hydrolysis by beta-lactamases. They are used (1) for infections caused by susceptible and moderately susceptible pneumococci, depending on the site of infection; (2) other streptococci, such as Streptococcus pyogenes, (including anaerobic streptococci); (3) meningococci; (4) non-beta-lactamase-producing staphylococci; (5) Treponema pallidum and other spirochetes; (6) Propionibacterium acnes and other gram-positive anaerobic bacilli; (7) non-diicile clostridia; and (8) actinomyces. See Table 30-4.

PENICILLINS The penicillins share a common chemical nucleus (6-aminopenicillanic acid) that conta... more PENICILLINS The penicillins share a common chemical nucleus (6-aminopenicillanic acid) that contains a beta-lactam ring essential to their biologic activity. Antimicrobial Action & Resistance The initial step in penicillin action is the binding of the medication to receptors, called penicillin-binding proteins. Aer penicillins attach to receptors, peptidoglycan synthesis is inhibited due to blockage of transpeptidation. The final bactericidal action is to remove an autolytic enzyme inhibitor in the cell wall, which results in cell lysis. Organisms that produce beta-lactamases (penicillinases) are resistant to some penicillins because the beta-lactam ring is broken. Only organisms actively synthesizing peptidoglycan (in the process of multiplication) are susceptible to penicillins and other beta-lactam antibiotics. Nonmultiplying organisms or those lacking cell walls are not susceptible. Microbial resistance to penicillins is associated with five mechanisms: (1) production of beta-lactamases, (eg, by staphylococci, gonococci, Haemophilus species, and coliform organisms, including extended-spectrum beta-lactamase (ESBL)-producing bacteria); (2) lack of penicillin-binding proteins or decreased ainity of penicillin-binding protein for beta-lactam antibiotic receptors (eg, resistant pneumococci, methicillin-resistant staphylococci, enterococci); (3) impermeability of the cell envelope (eg, by Pseudomonas species); (4) failure to activate autolytic enzymes in the cell wall-"tolerance," (eg, in staphylococci, group B streptococci); and (5) cell wall-deficient (L) forms or mycoplasmas, which do not synthesize peptidoglycans. 1. Natural Penicillins The natural penicillins include penicillin G for parenteral administration (aqueous crystalline for intravenous or benzathine penicillin G for intramuscular administration) or for oral administration (penicillin G and phenoxymethyl penicillin [penicillin V]). They are most active against gram-positive organisms and are susceptible to hydrolysis by beta-lactamases. They are used (1) for infections caused by susceptible and moderately susceptible pneumococci, depending on the site of infection; (2) other streptococci, such as Streptococcus pyogenes, (including anaerobic streptococci); (3) meningococci; (4) non-beta-lactamase-producing staphylococci; (5) Treponema pallidum and other spirochetes; (6) Propionibacterium acnes and other gram-positive anaerobic bacilli; (7) non-diicile clostridia; and (8) actinomyces. See Table 30-4.