beta-lactam antibiotics - cephalosporins targets - pbp’s activity - cidal - growing organisms...
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Beta-lactam antibiotics - Cephalosporins
Targets - PBP’s
Activity - Cidal - growing organisms (like the penicillins)
Principles of action - Affinity for PBP’s Permeability properties Stability to bacterial enzymes
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Cephalosporins
Development - Giuseppe Brodtzu - Sardinian sewage
Cephalosporin C - CephalothinNo meningeal penetrationFailed in meningococcal meningitis
Painful to give IM
AdvantagesCephalosporin nucleus - resistant to Staphylococcal penicillinaseCephalosporin nucleus - more readily modified
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Development of C’sporins
Generations - in response to clinical needs
First generation - Cephalothin (not used) Cefazolin
oral - Cephalexin, cefaclor
Activity - Broad spectrum:Gram positive Streptococci, S. aureusGram negative - E.coli, Klebsiella
No activity against Enterococci - different PBP’s
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Second generation C’sporins
CefuroximeCefoxitinCefotetan
70’s - Beta-lactamase’s recognized (H. influenzae)Anaerobic infections
Cefoxitin - Methoxy group - conferred beta-lactamase stability Induction of chromosomal beta-lactamases Bacteroides fragilis - enteric anaerobes
Cefuroxime - Respiratory tract infections - community acquired
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Kinetics of c’sporin binding
Affinity for receptor - PBP
Permeability characteristics of the porin
Beta-lactamase production - within periplasmic space
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Third generation C’sporins
80’s - Intensive care - nosocomial infections
Multi-Resistant Gram negative organisms
Chromosomal beta-lactamase - C’sporinaseInducible
Plasmid mediated enzymes - mutants withboth Penicillinase and C’sporinase activity
Permeability limitations
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Third generation c’sporins CefotaximeCeftriaxoneCeftazidimeCefipime Highly active - Cefotaxime - S. pneumo
N. meningitidis, gets across BBB
Ceftriaxone - even more active - Single dose IMget meningeal levels - Long half life !!!N. gonorrhoeae, use in unreliable patients -Cover S. pneumonia bacteremia
Use in meningitis -
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Ceftazidime/Cefepime - anti- Pseudomonas
Used the side groups which have increased permeability throughP.aeruginosa porins -
? Induction (low level) of chromosomal C’sporinase
Beta-lactamase stable -
less activity against gram positive organisms
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Cefepime – Fourth generation
Increased beta-lactamase stabilityAlso better Gram positive -
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Carbapenems
ImipenemMeropenem
Beta-lactam class - PBP-2 major targetPermeability - separate porin
Huge spectrum - Aerobes, anaerobeseverything EXCEPT
EnterococciStenotrophomonas etc.
Concern - CNS side effects - Imipenem ??
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Monobactams - Aztreonam
Only binds to Gram negative PBP’s
No real beta-lactam ring - therefore beta-lactamase stable
Narrow spectrum - Only aerobic gram negative rodsUse - instead of an aminoglycoside
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Use of the cephalosporins:
Increased - due to resistant S. pneumoniae - susceptible to cefotaxime and ceftriaxone
Gram negative infections - hospital acquired - selection ofresistant organisms
First generation - Oral - surgical prophylaxis - skin soft tissueinfections - taste good - “house cephalosprorin”
Second generation - Some oral - some parenteralSelected uses
Parenteral - Third generation
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Pharmacology
Charged - hydrophilic - do not enter phagocytic cells
Variably protein bound (Ceftriaxone - highly bound)Variable half-lives
Metabolism - Cefotaxime - Liver - desacetyl derivative - active
Excretion - Renal - Tubular secretion and glomerular filtration
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Beta-lactams – side effects
penicillin – c’sporin cross reactivity – 3-7%(depending on the drug)
Hypersensitivity – RashIgE-mediated allergy – Anaphylaxis
Major determinants – minor side effectsMinor determinants –MAJOR reactions
DiarrheaNeutropenia
CNS – high doses - especially the carbapenems
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C’sporins
Intrinsic resistance - enterococci - different targets
Acquired resistance - active change Acquisition of an enzymeInduction of an enzymeSelection of a mutation Alteration in permeability
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Vancomycin
History - Developed in the 50’s - anti-Staph drug
Re-”discovered” - MRSA - and MRSE - Staphylococci with altered PBP-2AmecA gene - no longer binds penicillin(C’sporins don’t bind either)
Target - D-ala-D-ala - pentapeptideblocks two steps in cell wall synthesis
Cidal - Only gram positives - Highly resistant S. pneumo
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Small glycoprotein (MWt @ 1,450) derived from Nocardia orientalis
Activity - most G(+) bacteria including Streptococci, Corynebacteria, Clostridia, Listeria, and Bacillus species.
Bactericidal at levels 0.5 - 3 mg/L
Staphylococci including ß-lactamase producing and methicillin resistant species are killed at levels <10 mg/L
Resistance - vancomycin resistant enterococcus (VRE)
Vancomycin - properties
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Vd @ 0.7 L/kg Protein binding @ 55% Elimination: > 90% renal
Half-life @ 7 hrs (with normal CLcr)
Vancomycin is not removed by standard HD or PD, but it is removed by CVVH
Vancomycin - Pharamacokinetic properties
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Side effects of vancomycin:
Red man syndrome - histamine-mediated erythematous flushing of the face, neck and trunk, a reaction which occurs during the infusion, and may be associated with hypotension.
Nephrotoxicity and ototoxicity may occur in < 1% of pts especially those receiving other "toxic' drugs
like aminoglycosides.
A relationship between vancomycin level and nephrotoxicity or ototoxicity has not been established.
It is now widely believed that the earlier reports of nephrotoxicity may have been related to impurities in the product.
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Vancomycin and Resistant S. pneumoniae
Penicillin MIC’s <0.1 - S; 0.1-1= RR; >2.0 Resistant
Alternate therapy - Pneumonia/Bacteremia - Cefotaximeor Ceftriaxone
? Meningitis - Can’t achieve levels -
Vancomycin - high doses - gets into CSF
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Vancomycin resistant enterococci
Increased 34 fold from 0.3% to 7.9% NISS 1989 - 1993
Initially associated with ICU’s
Larger hospitals
Lack of alterative therapy
? Spread of genes involved to S. aureus and S. epidermidis
Non ICU’s
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Cephalosporins - what to remember
Developed in response to clinical needs -Grouped by “generation”Learn properties of a prototype from each generation
Extremely widely used -
Safe - Side effects specific to individual members of the familyas well as the family as a wholeNot necessarily cross reaction with penicillinhypersensitivity
Aztreonam - Gram negs - narrow
Imipenem/Meropenem - everything “except”
Vanco - need to know well