Staphylococcus aureus…………quickly posed a problem Produce a B-lactamase (Penicillinase)

1. Staphylococcus aureus…………quickly posed a problem • Produce a B-lactamase (Penicillinase) • Plasmid mediated (easily spread) • Secreted into the surrounding medium • Destroyed the Penicillin before it could reach the PBP’s S O S O S O

2. CH3 O O N R2 C NH S CH3 CH3 R1 N O COOH R1 R2 Oxacillin H H Cloxacillin Cl H Dicloxacillin Cl Cl Isoxazoyl Penicillins

3. If chemical modification can overcome B-lactamase activity Maybe chemical modification can also increase spectrum of activity ?

4. NH2 O C NH S CH3 CH3 N O COOH Ampicillin

5. Aminopenicillins • Modified to broaden their spectrum of activity • better binding affinity to the PBP’s of • Enterococci • Listeria • Some Gram –ve bacteria • But a cost of slight decreased activity against Streptococci • S. pneumonia / Group A strept • Not stable to the B-lactamase produced by S. aureus • Inactivated by many of the B-lactamases produced by Gram –ves • (limited gram negative coverage)

6. Amino-Penicillin • Amoxicillin • Ampicillin • Bacampicillin First penicillins discovered to be active against gram negative rods like E. coli and H. Influenzae.

7. Amino-Penicillin • Same coverage like Pen VK plus: - Listeria monocytogenes - Enterococcus - Proteus mirabilus - E coli - H. flu

8. Amino-Penicillin • Amoxicillin is more completely absorbed than Ampicillin. • Serum levels are twice as high. • Small amount is left in GI tract, so less diarrhea. • However, more complete absorption makes it less effective for Shigella enteritis. • Both have same antibacterial spectrum. • Bacampicillin is more expensive and no advantage.

9. Amino-Penicillin Primarily used for: • Otitis media • Sinusitis • Bronchitis • Urinary tract infection esp. Enterococcus • Bacterial diarrhea • Salmonella infection • Shigella infection. H. Influenzae and E. Coli are increasingly becoming resistant.

10. Maybe if we change its structure a lot….. …we will get even more gram negative coverage !

11. Carboxypenicillins • Carbenicillin • 1st penicillin developed with expanded gram –ve activity that • included anti-pseudomonal activity • But decreased activity against Streptococci and Enterococci • Required large doses to be effective clinically • too toxic to be used clinically • Replaced by the next drug developed in this class…Ticarcillin

12. Ureidopenicillins • similar to Ampicillin wrt Streptococcal activity • Enterococcal activity • Better anti-pseudomonal activity then Ticarcillin • Better Klebsiella activity then Ticarcillin (75% vs 5%) • Not orally absorbed thus available only IV • 3 preparations Azlocillin (no longer available) • Mezlocillin (USA) • Piperacillin (Canada / USA) • Piperacillin is also available as a combination with a • B-lactamase inhibitor to increase its spectrum of activity • (Piperacillin + Tazobactam = Pip/Tazo)

13. O C NH S CH3 CH3 N O COOH Penicillin G

14. O CH3 C N NH O N C NH S CH3 O O CH3 N O COOH Piperacillin

15. 5 Classes of Penicillins Natural Penicillins Penicillin G / Penicillin V Penicillinase Resistant Penicillins Methicillin Nafcillin Isoxazoly Penicillins (Cloxacillin / Dicloxacillin / Oxacillin / Flucloxacillin) Aminopenicillins Ampicillin / Amoxicillin Carboxypenicillins Ticarcillin Ureidopenicillins Piperacillin / Mezlocillin / Azlocillin

16. B-lactamases Chromosomal Plasmid Inducible Constituitive High [ ] High [ ] Low [ ] TEM 1-27 SHV 1-8 OXA 1-3 PSE 1-5 SPACE Serratia Pseudomonas Acintobacter Citrobacter Enterobacter Can NOT be overcome by Can be overcome by B-lactam – B-lactamase Inhibitor B-lactam – B-lactamase Inhibitor Combinations Combinations

17. Antibiotics Biosynthetic Chemical Penicillin (1945)

18. Antibiotics Biosynthetic Chemical Penicillin (1945) Search for other Compounds Chemical Modification

19. We like to think we are smart Chemical Manipulation

20. Bacteria have been fighting each other since before we evolved Nature has been doing chemical modifications for millions of years There have been many chemical modifications

21. R S CH3 CH3 N O COOH B-lactam

22. R C CH3 R S CH3 CH3 CH3 N N O COOH O COOH Carbepenem B-lactam

23. Carbapenems 1st isolated from Streptomyces cattleya in 1976 Base compound was thienamycin - methylene replacement for the Sulphur in the 5 membered ring R C CH3 R S CH3 CH3 CH3 N N O COOH O COOH Carbepenem B-lactam

24. Carbapenems • stable to B-lactamases • due to the side chain being in a trans rather then the • typical cis configuration seen in B-lactams R S R N N O O B-lactam Carbapenem

25. 2 Compounds in clinical use : Imipenem Meropenem Imipenem Meropenem

26. Imipenem Spectrum of Activity Gram +ve cocci - Staphylococcus aureus - Streptococci sp - S. pneumoniae - Enterococci Gram –ve rods - except Pseudomonas cepacia and Xanthomonas maltophilia Anaerobes - except Clostrium difficile and a % of Bacteroides sp

27. Mechanism of Action - binds to the PBP’s leading to cell lysis Considered Bacterocidal (except for Enterococcus – bacteriostatic) Resistance - not due to the typical B-lactamases 1. Enzyme that will hydrolyze the imipenem 2. Loss of an outer membrane protein that would otherwise facilitate entry

28. R S CH3 R S CH3 CH3 CH3 N N O COOH O COOH Side Chain Modifications Penicillin R C CH3 R CH3 S N R O COOH N O Carbapenem COOH Cephalosporin

29. Cephalosporins 1940’s Cephalosporium acremonium was isolated from the seawater At the harbour sewage outlet of Cagliari, Sardinia Produced a substance that inhibited the growth of both gram +ve and gram –ve bacteria 1948 a culture of the fungus C. acremonium was sent to Oxford 3 antimicrobial substances produced by this fungus were identified Cephalosporin P gram +ve activity only Cephalosporin N re-identified as a penicillin Cephalosporin C foundation for current Cephalosporin family

30. Cephalosporin C - B-lactam ring fused to a 6 membered dihyrdothiazine ring

32. Mechanism of Action • Binds to PBP’s and interferes with synthesis of the peptidoglycan • cell wall • Bactericidal • Stable to many B-lactamases produced by gram +ve and gram –ve’s • Better ability to penetrate the outer LPS membrane of gram –ve bacteria LPS Peptidoglycan Cell membrane Gram –ve Gram +ve

33. Mechanisms of Resistance • Alteration of the PBP target • Production of B-lactamases that inactivate cephalosporins • (Cephalinosporinases) • Decreased ability of the Antibiotic to reach its target • (LPS of gram –ve bacteria) PBP’s B-Lactamases Cell Memebrane Cell Wall Lipopolysaccharide (LPS)

34. Decreased affinity of PBP’s to bind cephalosporins are seen in • Streptococcus pneumoniae • Haemophilus influenzae • Neisseria gonorrhea • MRSA • Major mechanism of resistance in gram +ve bacteria

35. Cephalosporinases (serine proteases) hydrolyze the amide bond of the B-lactam ring thus inactivating the antibiotic Major mechanism of resistance in gram –ve bacteria Can be encoded chromosomally or on plasmids Can be constitutive or inducible Effectiveness depends on Affinity of the Cephalosporinase for the Cephalosporin Concentration of the Cephalosporinase produced Concentration of the Cephalosporin present

36. Plasmid mediated B-lactamases are often produced in large numbers • Number of different classes (TEM, SHV, etc) • Mutations lead to B-lactamases with increased spectrum of activity • ESBL’s (Extended Spectrum B-lactamases) • resistance to the 3rd generation cephalosporins • also will destroy the monobactams (Aztreonam) • however the Carbapenems are not affected (Imipenem / Meropenem)

38. Classification – based on the spectrum of activity 1st generation : gram +ve cocci 2nd generation : variable g +ve but increased gram –ve rod activity 3rd generation : variable g +ve but greatly increased g -ve activity 4th generation : g +ve and increased g -ve activity

41. 1st Generation Half Life Peak Protein CSF [ ] Bound Penetration Cephalothin (Ceporacin) IV 1hr 30 70 - Cefazolin (Ancef) IV 1hr 80 80 - Cephalexin (Keflex) po 1hr 18 10 - Cefadroxil (Duricef) po 1hr 16 20 - 2nd Generation Cefoxitin (Mefoxin) IV 0.8 hr 150 70 - Cefotetan (Cefotan) IV 3.5 hrs 230 90 - Cefuroxime (Kefurox/Ceftin) IV / po 1.3 hrs 100 35 1-2/- Cefaclor (Ceclor) po 0.8 hrs 13 25 - Cefprozil (Cefzil) po 1.2 hrs 10 42 - 3rd Generation Cefotaxime (Claforan) IV 1.0 hrs 130 35 5.6-44 Ceftriaxone (Rocephin) IV 8 hrs 250 90 1.2-39 Ceftizoxime (Cefizox) IV 1.7 hrs 1330 30 0.5-29 Ceftazidime (Fortaz) IV 1.8 hrs 160 17 0.5-30 4th Generation Cefepime (Maxipime) IV 2.1 hrs130 20 3.3-5.7

42. 1st Generation Half Life Peak [ ] Protein Bound Cephalothin (Ceporacin) IV 1hr 30 70 % Cefazolin (Ancef) IV 1hr 80 80 % Cephalexin (Keflex) po 1hr 18 10 % Cefadroxil (Duricef) po 1hr 16 20 % What does this mean ? ….. Best 1st Generation Oral Drug is Cephalexin (Keflex) - higher peak concentration - less protein binding -- means more free drug to act on bacteria Best 1st Generation IV drug is Cefazolin (Ancef) - higher peak concentration - even though more is protein bound (80vs70%), the higher peak means.. -- more free drug to act on bacteria NO CSF Penetration thus do not use in Meningitis

43. 2nd Generation Half Life Peak Protein CSF [ ] Bound Penetration Cefoxitin (Mefoxin) IV 0.8 hr 150 70 - Cefotetan (Cefotan) IV 3.5 hrs 230 90 - Cefuroxime (Kefurox/Ceftin) IV / po 1.3 hrs 100/9 35 1-2/- Cefaclor (Ceclor) po 0.8 hrs 13 25 - Cefprozil (Cefzil) po 1.2 hrs 10 42 - Cefoxitin Cefuroxime Cefaclor Cefprozil

44. 3rd Generation Half Life Peak Protein CSF [ ] Bound Penetration Cefotaxime (Claforan) IV 1.0 hrs 130 35 5.6-44 Ceftriaxone (Rocephin) IV 8 hrs 250 90 1.2-39 Ceftizoxime (Cefizox) IV 1.7 hrs 1330 30 0.5-29 Ceftazidime (Fortaz) IV 1.8 hrs 160 17 0.5-30 Cefixime (Suprax) po 3.5 hrs Cefotaxime Ceftriaxone

45. R S CH3 R S CH3 CH3 CH3 N N O COOH O COOH Side Chain Modifications Penicillin R C CH3 R CH3 S N R O COOH N O Carbapenem COOH Cephalosporin

46. R S CH3 R S CH3 CH3 CH3 N N O COOH O COOH Side Chain Modifications Penicillin R C CH3 R CH3 S Monobactam N R O COOH N O Carbapenem COOH Cephalosporin

47. Monobactams Isolated from Chromobacterium violaceum in 1981 Monocyclic B-lactam antibiotic No activity against gram +ve bacteria or anaerobes Binds to PBP’s of gram –ve bacteria only Hydrolyzed by cephalosporinases of Pseudomonas cepacia Xanthomonas maltophilia Acinitobacter Klebsiella oxytoca Haemophilus

48. Pharmacology • no oral absorption thus available as IV formulation only • Renal clearance • Complications • mild rash • Mild transaminitis • NO MAJOR SIDE EFFECTS • Lack of cross reaction with other B-lactam antibiotics thus • can be used in Pen/Ceph allergic patients

49. Aztrenoam • monobactam in clinical use • Limited to Gram –ve infections only

50. Penicillins Carbepenems Monobactams Cephalosporins B-lactamase Inhibitors Structural Overview