Beta-lactams 1 รศ. พญ. มาล ยา มโนรถ ภาคว ชาเภส ชว ทยา จ ดประสงค การศ กษา เม อส นส ดการเร ยนการสอน และการศ กษาด วยตนเองเพ มเต ม น กศ กษาสามารถ 1. อธ บายกลไกการออกฤทธ และกลไกการด อยาของยากล ม penicillins 2. ทราบถ งชน ดของยาในกล ม penicillins 3. ทราบถ งขอบเขตการออกฤทธ ต านจ ลช พ,เภส ชจลนศาสตร, และประโยชน ทางคล น กของยากล ม penicillins 4. บอกผลข างเค ยงท ส าค ญของยากล ม penicillins Beta-Lactam Antibiotics 1. Penicillins 2. Cephalosporins 3. Monobactams 4. Carbapenems Bacteria 1. Aerobic G - cocci : Gonococcus, Meningococcus G + cocci : Pneumococcus, Streptococcus, Staphylococcus, Enterococcus faecalis G - rods : Coliform (E.coli,Klebsiella, Enterobacter, Serratia, Proteus, Providencia) : Shigella, Salmonella, Haemophilus, Pseudomonas G + rods : Bacillus sp, Nocardia, Listeria 2. Anareobic G - : Bacteroides fragilis, Fusobacterium G + : Peptococcus, Peptostreptococcus, Clostridia 1
Penicillins 1929 : Fleming Colonies of staphylococci lysed on a plate, contaminated with a Penicillium mold 1940 : Chain, Florey producing : first penicillins from cultures of Penicillium notatum 1949 : Clinical use : penicillin G destruction by beta-lactamase relative inactivity against most G- bacteria 1957 : Isolation : 6-aminopenicillanic acid Thiazolidine ring [A] Beta-lactam ring [B] Acidic radicals [R] Chemistry semisynthetic penicillins Penicillins 1. Penicillins penicillin G (prototype) 2. Antistaphylococcal penicillins methicillin (prototype) cloxacillin, dicloxacillin, nafcillin penicillin V susceptible to hydrolysis by beta-lactamase resistant to staphylococcal beta-lactamases 3. Extended-spectrum penicillin ampicillin amoxicillin Mechanism of action binding to penicillin-binding proteins (PBPs) inhibition of transpeptidase enzymes activation of autolytic enzymes piperacillin ticarcillin 2
Pharmacokinetics PO : differ greatly for different penicillins (depending in part on their acid stability, protein binding) Dicloxacillin, ampicillin, amoxicillin are acid stable and relative well absorbed Absorption of most oral penicillins (except amoxicillin) is impaired by food : should be administered at least 1-2 hrs before or after a meal After parenteral administration, absorption of most penicillins is complete and rapid Penicillins are widely distributed in body fluids and tissues are polar molecules (concentration within the cells is less than in extracellular fluids) Procaine and benzathine penicillins are formulated to delay absorption prolonged blood and tissue concentrations Penicillins concentrations in most tissues are equal to those in serum Penetration into the eye, the prostate, and the CNS is poor (except active inflammation of meninges) Rapidly excreted by the kidney into the urine glomerular filtration (10%) tubular secretion (90%) Nafcillin is primarily cleared by biliary excretion Plasma half-lives of most penicillins vary from 0.5-1 h. Activity Penicillin G 1600 units/mg 1 million unit of penicillin = 0.6 gm Most semisynthetic penicillins : weight Penicillin V 125 mg = 200,000 units Clinical Uses 1. Penicillin : Penicillin G : therapy of infections caused by common streptococci, pneumococci, meningococci, gram-negative bacilli, spirochete Penicillin V : indicated only in minor infections Benzathine penicillin and procain penicillins G : treatment of beta-hemolytic streptococcal pharyngitis, syphilis 3
2. Antistaphylococcal penicillins Cloxacilln, nafcillin PO : mild localized staphylococcal infections relatively acid-stable, well absorb from the gut, food interferes with absorption (1 hr before or after meal) IV : serious systemic infections 3. Extended-spectrum penicillin wider spectrum of antibacterial activity than penicillin G but remain susceptible to penicillinase Ampicillin : PO : well absorbed, food interfere, enterohepatic circulation Amoxicillin : PO : rapidly & completely absorbed from GIT, food does not interfere Piperacillin & Ticarcillin * have activity against several G- rods (pseudomonas, enterobacter, klebsiella species) * synegistic actions when used with aminoglycosides against such organism * are susceptible to penicillinase Adverse Reaction 1. Allergy : urticaria, severe pruritus, fever, nephritis anaphylactic shock (very rare 0.05% of recipients) 2. Gastrointestinal disturbances : nausea, diarrhea (oral penicillin, especially with ampicillin) 3. Cationic toxicity : toxic effect from Na+ or K+ (high dose penicillin salt are used in patient CVS or renal disease) 4. Pseudomembranous colitis (related to overgrowth and production of a toxin by Clostridium difficile (PO > parenteral penicillins) Resistance to Penicillin 1. Formation of beta-lactamases (major mechanism) 2. Structural change in target PBPs 4
Beta-lactamase Inhibitors Clavulanic acid, sulbactam, tazobactam beta-lactam molecules very weak antibacterial action protect hydrolyzable penicillins Clavulanic acid + amoxicillin Clavulanic acid + ticarcillin Sulbactam + ampicillin Augmentin Timentin Unasyn 5