CEPHALOSPORINS, RESISTANCE TO GRAM NEGATIVE BACTERIA

CEPHALOSPORINS changing resistance patterns CLSI Guidelines 2010:

CEPHALOSPORINS changing resistance patterns CLSI Guidelines 2010 Dr.T.V.Rao MD Dr.T.V.Rao MD 1

Introduction to Cephalosporins..:

Introduction to Cephalosporins . . Cephalosporins were first isolated from cultures of Cephalosporium acremonium from a sewer in 1948 by Italian scientist, Giuseppe Brotzu The first agent cephalothin ( cefalotin ) was launched by Eli Lilly in 1964 Dr.T.V.Rao MD 2

Cephalosporins ….:

B-Lactam antibiotics ( similar to penicillin's) Broad spectrum in action. Act by inhibition of cell wall synthesis Bactericidal Inactive against : enterococci, MRSA, legionella , mycoplasma, chlamydia spp. Widely used in surgical procedures to reduce the risk of post operative infections Cephalosporins …. Dr.T.V.Rao MD 3

Antimicrobial activity of Cephalosporins:

The site of action of beta-lactam antibiotics is the penicillin binding proteins (PBPs) on the inner surface of the bacterial cell membrane that are involved in the synthesis of the cell wall Cephalosporins are bactericidal agents All bacterial cells have a cell wall that protects them. Cephalosporins disrupt the synthesis of the peptidoglycan layer of bacterial cell walls, which causes the walls to break down and eventually the bacteria die. Antimicrobial activity of Cephalosporins Dr.T.V.Rao MD 4

Classification is based on spectrum of activity :

Classification is based on spectrum of activity Cephalosporins are grouped into "generations " based on their spectrum of antimicrobial activity. The first cephalosporins were designated first generation while later, more extended spectrum cephalosporins were classified as second generation cephalosporins. So continued Generations Dr.T.V.Rao MD 5

Basis of Classification …:

Basis of Classification … Each newer generation of cephalosporins has significantly greater gram-negative antimicrobial properties than the preceding generation Fourth generation cephalosporins, however, have true broad spectrum activity Dr.T.V.Rao MD 6

1st generation Cephalosporins:

1 st generation C ephalosporins First generation cephalosporins are moderate spectrum agents Effective against gram +ve aerobes They are effective for treating staphylococcal and streptococcal infections and therefore are alternatives for skin and soft-tissue infections, as well as for streptococcal pharyngi tis. Dr.T.V.Rao MD 7

The 1st generation cephalosporins are::

Dr.T.V.Rao MD 8 Cefadroxil Cephalexin Cephaloridine Cephalothin Cephapirin Cefazolin Cephradine The 1 st generation cephalosporins are :

1st Generation:

Active against G+ cocci ( except. Enterococci & MRSA ): s.pneumoniae, s.pyogenes,s. aureus, S. epidermidis Indicated for streptococcal pharyngitis ( e.g. cephalexin) Commonly used ( eg. Cefazolin) as prophylactic for surgical procedures. Modest activity against G- bacteria 1 st Generation Dr.T.V.Rao MD 9

2nd generation Cephalosporins:

2 nd generation Cephalosporins Their antibacterial spectrum is broader than that of 1 st generation cephalosporins and includes some gram -ve pathogens They are also more resistant to beta-lactamase They are useful agents for treating upper and lower respiratory tract infections and sinusitis Dr.T.V.Rao MD 10

2nd generation cont...:

2 nd generation cont ... These agents are also active against E. coli, Klebsiella and Proteus, which makes them potential alternatives for treating urinary tract infections caused by these organisms Dr.T.V.Rao MD 11

2nd Generation Cephalosporins ..:

Dr.T.V.Rao MD 12 2 nd Generation Cephalosporins .. Cefoxitin Cefuroxime Cefuroxime axetil Cefaclor Cefprozil

3rd generation Cephalosporins:

3 rd generation Cephalosporins They have an extended spectrum of action against gram -ve organisms Resistant to beta-lactamases Dr.T.V.Rao MD 13

3rd generation cont...:

3 rd generation cont... The parenteral third generation cephalosporins (ceftriaxone and cefotaxime) have excellent activity against most strains of Streptococcus pneumoniae, including the vast majority of those with intermediate and high level resistance to penicillin Dr.T.V.Rao MD 14

Third Generation Cephalosporins:

Third Generation Cephalosporins Ceftriaxone Cefotaxime Ceftazidime Cefoperazone Cefixime Dr.T.V.Rao MD 15

THIRD GENERATION :

THIRD GENERATION They have enhanced G- activity, H. influenza, N. meningitidis, N.gonorrhea, P. aeruginosae, M. catarrhalis, E.coli, most Klebsiella Ceftriaxone h as long half-life . Not advised in neonates (interferes with bilirubin metabolism ) Cefotaxime preferred in neonate ( does not interfere with bilirubin metabolism ), as may ceftriaxone. Ceftazidime & cefoperazone have excellent activity against P.aeruginosa. Cefixime has similar activity to amoxicillin & Cefaclor for actute otitis media Dr.T.V.Rao MD 16

4th generation cephalosporins:

4 th generation cephalosporins 4 th generation cephalosporins are extended spectrum agents with similar activity against gram-positive organisms as first generation cephalosporins. They also have a greater resistance to beta-lactamases than the third generation cephalosporins. Many can cross blood brain barrier and are effective in meningitis. Dr.T.V.Rao MD 17

4th Generation Cephalosporins...:

4 th Generation Cephalosporins ... Cefepime Cefluprenam Cefozopran Cefpirome Cefquinome Dr.T.V.Rao MD 18

Fourth Generation Cefipime :

Fourth Gener ation Cefipime Active against G+ bacteria > than Cefazolin against s. pyogenes, S.pneumoniae but lower against s. aureus. Similar to cefotaxime against E.coli & K. pneumoniae but < for p. aeruginosa. Dr.T.V.Rao MD 19

Pharmacokinetic consideration:

They are organic acids and are hydrophilic They generally have poor oral bioavailability as they unstable in acid environments They are readily excreted by the kidneys, via tubular secretion in the proximal convoluted tubule. This results in high concentrations of the drug in urine. Exceptions are: Cephalexin which is stable in acid and so suitable for oral dosing. Cefoperazone is excreted in bile rather than in urine. Pharmacokinetic consideration Dr.T.V.Rao MD 20

Why Cephalosporins are Widely Prescribed Antibiotics:

Why Cephalosporins are Widely P rescribed A ntibiotics Broad spectrum of activity Stability to -lactamase Oral and parenteral preparations Widely accepted Treats ‘day to day’ as well as ‘serious infections’ High safety profile Dr.T.V.Rao MD 21

Cephalosporins -Limitations:

Dr.T.V.Rao MD 22 Cephalosporins -Limitations Emerging resistance patterns III & IV generation cephalosporins were available only as parenteral formulations Pharmacoeconomics

Why detect ESBL producers?:

Why detect ESBL producers? ESBL producers may: Appear Sensitive to some cephalosporins in vitro Show major inoculum effects Fail in therapy, despite appearing susceptible Dr.T.V.Rao MD 23

Detection Strategy: step 1:

Detection Strategy: step 1 Ref http ://www.hpa.org.uk Screen Enterobacteriaceae with : Cefpodoxime- best general ESBL substrate Cefotaxime & ceftazidime- good substrates for CTX-M & TEM/SHV, respectively Spread of CTX-M into community means screening must be wider than before Dr.T.V.Rao MD 24

Detection of ESBLs: step 2:

Detection of ESBLs: step 2 Seek ceph/clav synergy in ceph R isolates Double disc Combination disc Etest Ref http://www.hpa.org.uk Dr.T.V.Rao MD 25

Double Disk Method:

Double Disk Method Dr.T.V.Rao MD 26

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Etest for ESBLs Cefotaxime Cefotaxime + C lavulanate Dr.T.V.Rao MD 27

Pitfalls in ESBL detection:

Methods optimised for E. coli & Klebsiella More difficult with Enterobacter clavulanate induces AmpC; hides ESBL Best advice is to do synergy test (NOT SCREEN) with 4 th gen cephalosporins Pitfalls in ESBL detection Dr.T.V.Rao MD 28

Synergy tests with 4-gen cephalosporins:

Synergy tests with 4-gen cephalosporins Cefepime/clav (Mast & AB Biodisk) Cefpirome clav (Oxoid) Devt. driven by spread of clonal E. aerogenes with TEM-24 in Belgium & France Sensitivity for weak ESBLs remains to be proven Cefpirome & cefepime products need comparison Dr.T.V.Rao MD 29

Bacteria not to test for ESBLs:

Bacteria not to test for ESBLs Acinetobacter Often S to clavulanate alone S. maltophilia +ve result by inhibition of L-2 chromosomal b -lactamase, ubiquitous in the species Dr.T.V.Rao MD 30

Role of CLSI in Revising Breakpoints in Antibiotic Resistance:

Briefly, revising breakpoints involves systematic review of microbiological, pharmacologic, and clinical data. Recognized experts, sponsors (pharmaceutical industry), and regulators participate in the process which includes discussions at public meetings of the CLSI Subcommittee on Antimicrobial Susceptibility Testing that take place twice a year. When establishing original breakpoints for new agents, controlled clinical trial data are required Role of CLSI in Revising Breakpoints in Antibiotic Resistance Dr.T.V.Rao MD 31

Follow the New Guidelines CLSI 2010:

Follow the New Guidelines CLSI 2010 Guidelines for cephalospins for Enterobacteriaceae in accordance with the 2010 Clinical Laboratory Standards Institute (CLSI) recommendations. The following changes will be made to comply with the CLSI. Dr.T.V.Rao MD 32

Why do breakpoints sometimes need to be revised? :

Why do breakpoints sometimes need to be revised? Breakpoints need to be revised due to changing resistance mechanisms and bacterial population distributions, changing science leading to a better understanding of the pharmacologic determinants of clinical response, and adoption of “best practices” by clinicians. Dr.T.V.Rao MD 33

Enterobacteriaceae - Rapid Spread of resistance:

Enterobacteriaceae - R apid S pread of resistance The rapid and disturbing spread of: extended-spectrum ß-lactamases AmpC enzymes carbapenem resistance metallo-β-lactamases KPC and OXA-48 β-lactamases quinolone resistance Dr.T.V.Rao MD 34

What breakpoints were revised in 2010? :

What breakpoints were revised in 2010? Select cephalosporin and aztreonam breakpoints for Enterobacteriaceae were revised as noted below (for comparison, the old breakpoints are included): Dr.T.V.Rao MD 35

Extended-Spectrum β-Lactamases:

β -lactamases capable of conferring bacterial resistance to the penicillin's first-, second-, and third-generation cephalosporins aztreonam (but not the cephamycins or carbapenems) These enzymes are derived from group 2b β -lactamases (TEM-1, TEM-2, and SHV-1) differ from their progenitors by as few as one AA Extended-Spectrum β -Lactamases Dr.T.V.Rao MD 36

CTCTX-M-type ESBLs X-M-type ESBLs :

Until 2000, most ESBL producers were hospital Klebsiella spp. with TEM and SHV mutant β -lactamases Now, the dominant ESBLs across most of Europe and Asia are CTX-M enzymes, which originated as genetic escapes from Kluyvera spp Currently recognized as the most widespread and threatening mechanism of antibiotic resistance, both in clinical and community settings 80% of ESBL-positive E. coli from bacteraemias in the UK and Ireland are resistant to fluoroquinolones 40% are resistant to gentamicin CT CTX-M-type ESBLs X-M-type ESBLs Livermore, DM J. Antimicrob. Chemother 2009 Dr.T.V.Rao MD 37

Enterobacteriaceae: Revised Breakpoints for Cephalosporins :

Agent CLSI 2009 CLSI 2010 S I R S I R Cefazolin ≤8 16 ≥32 ≤1 2 ≥4 Cefotaxime ≤8 16-32 ≥64 ≤1 2 ≥4 Ceftriaxone ≤8 16-32 ≥64 ≤1 2 ≥4 Ceftazidime ≤8 16 ≥32 ≤4 8 ≥16 Aztreonam ≤8 16 ≥32 ≤4 8 ≥16 Cefipime ≤8 16 ≥32 ≤8 16 ≥32 Enterobacteriaceae : Revised Breakpoints for Cephalosporins Dr.T.V.Rao MD 38

Disk diffusion breakpoints (mm): :

Agent Old (M100-S19) Revised (M100-S20) S I R S I R Cefazolin ≥ 18 15-17 ≤14 NA NA NA Cefotaxime ≥ 23 15-22 ≤14 ≥ 26 23-25 ≤22 Ceftizoxime ≥20 15-19 ≤14 ≥ 25 22-24 ≤21 Ceftriaxone ≥21 14-20 ≤13 ≥ 23 20-22 ≤19 Ceftazidime ≥18 15-17 ≤14 ≥ 21 18-20 ≤17 Aztreonam ≥22 16-21 ≤15 ≥ 21 18-20 ≤17 S – susceptible I – Intermediate R – Resistant . Disk diffusion breakpoints (mm): Dr.T.V.Rao MD 39

Following MIC breakpoints were reevaluated for Enterobacteriaceae but were not revised :

Agent M100-S19 M100-S20 S I R S I R Cefuroxime ≤8 16 ≥ 32 ≤ 8 16 ≥32 Cefepime ≤8 16 ≥32 ≤8 16 ≥32 Cefotetan ≤16 32 ≥64 ≤16 32 ≥64 Cefoxitin ≤8 16 ≥32 ≤8 16 ≥32 S – susceptible I – Intermediate R – Resistant F ollowing MIC breakpoints were reevaluated for Enterobacteriaceae but were not revised Dr.T.V.Rao MD 40

Why were the breakpoints for cefepime and cefuroxime (parenteral) not revised? :

Dr.T.V.Rao MD 41 Why were the breakpoints for cefepime and cefuroxime (parenteral) not revised ? The cefepime breakpoints were not revised based upon clinical trial data and PK-PD evaluations. The clinical trial data showed cefepime efficacy for patients infected with isolates that tested cefepime susceptible (MIC ≤8 μg/ml), but produced an ESBL

Why are there no disk diffusion breakpoints for Cefazolin? :

Dr.T.V.Rao MD 42 Why are there no disk diffusion breakpoints for Cefazolin ? Studies have not yet been completed to identify the zone diameter breakpoints that correlate with the revised MIC breakpoints for Cefazolin. Initial studies did not reveal clear zone diameter breakpoints and disk diffusion testing of Cefazolin may require a new disk with alternate disk content.

Cephalothin group:

Dr.T.V.Rao MD 43 Cephalothin group Cephalothin is now classified under Test/Report Group U for Enterobacteriaceae. Results for cephalothin can be used to represent activities of several other oral FDA-approved agents for treatment of urinary tract infections which include cefadroxil, cefpodoxime, cephalexin, and loracarbef.

Need for Changing Recommendations:

The ESBL testing recommendations were to be a short term solution to address a new mechanism of resistance. Subsequently, additional mechanisms of resistance have been identified (e.g., new types of ESBLs and AmpC-like enzymes) and with increased frequency multiple enzymes are identified in a single isolate which can complicate ESBL testing (1). These issues coupled with improved understanding of the PK-PD determinants of efficacy with cephalosporins and monobactams resulted in the decision to revise the breakpoints. Need for Changing Recommendations Dr.T.V.Rao MD 44

Measuring the Revised Zones is Advantageous:

The revised breakpoints eliminate the need to perform ESBL screen and confirmatory tests for making treatment decisions . Phenotypic tests for ESBL detection and confirmation are less accurate when multiple enzymes are present (e.g., false-negative results occur when isolates express both ESBLs and AmpC-type enzymes) (13) and the presence of multiple enzymes are more common in contemporary isolates (4, 8). The MIC of an isolate correlates better with clinical outcome than knowledge of resistance mechanisms (e.g., ESBLs) Measuring the Revised Zones is Advantageous Dr.T.V.Rao MD 45

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