Cell Wall Synthesis Inhibitors

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Classes

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Penicillins (b lactamase ring)
Cephalosporins (b lactamase ring) and cephamycins
Vancomycin
Carbapenams
Monobactams
Beta lactamase inhibitors

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Resistance to b lactams

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-bacteria produces beta lactamase
-pencillin binding protein changes
-solutiton for both

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Penicillins

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All penicillins contain a beta lactam ring
Penicillins vary in their bioavailability because of their varied resistance to gastric acid
Usually excreted unchanged in the urine (more polar compounds) recycled and exploited in wwII
Normally does not cross BBB
Crosses BBB in meningitis. Meninges are inflammed causing increased permeability

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Probenecid

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competitively inhibits the renal tubular secretion of penicillin
Thus it increases the concentration of penicillin and prolongs its activity. Not excreted in the urine

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Resistance to penicillins

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Most common mechanism: production of beta lactamases (penicillinase)
S. Aureus changes PBP for Methicillin

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Group 1 Narrow spectrum penicillins

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penicillinase susceptible

Penicillin G (given IM)
Limited spectrum of action
Highly susceptible to beta lactamases

Drug of choice in the management of syphilis given intra muscular (Treponema pallidum)

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Penicillin G

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Drug of choice in the management of syphilis given intra muscular (Treponema pallidum)

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Group 2 Narrow spectrum

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(penicillinase resistant)
Methicillin, nafcillin & oxacillin
Methicillin causes interstitial nephritis
Used in the Rx of staphylococcal infections
2nd DOC

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Group 3 Broad spectrum penicillins

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(penicillinase susceptible)
Ampicillin & Amoxicillin
Wider spectrum of action than penicillin GSusceptible to inactivation by beta lactamases
Uses include: all the uses of penicillin G plus
Infections due to enterococci, Listeria monocytogenes, E. coli, Proteus mirabilis, Hemophilus influenza
ALWAYS used w/ beta lactamase inhibitors

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Group 4 Broad spectrum penicillins

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penicillinase resistant)
Piperacillin & Ticarcillin
Has good activity against gram negative rods
E.g. ***Pseudomonas, Enterobacter
Synergestic action with aminoglycosides!!!

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Beta lactamase inhibitors

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**Clavulinic acid, Sulbactam and Tazobactam
No antibacterial effect alone just inhibits beta-lactamase enzyme
Sold as fixed drug combination with penicillinase suspectible drugs (broad spectrum) to increase spectrum of action

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Adverse effects of penicillins

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Any type of hypersensitivity; 1-4,v minor to anphylactic shock
-incomplete cross resistance; if one type of pencillin gives you a rash, a different type may-or-may not; but contradiciated if any reaction

ALL antibiotics GIVEN orally destroy normal flora; complaining of diahreea and bloody diahreaa

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Monobactams

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active only against Gr negative organisms)
Cell Wall Synthesis Inhibitors
only drug; Aztreonam
-use when cannot use penecillin/cephalosporin

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Carbepenem

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(broadest spectrum gram+ -ve and anerobes
Cell Wall Synthesis Inhibitors
Imipenem, Meropenem, Ertapenem
Low susceptibility to beta lactamases
Wide activity against Gr positive cocci, Gr negative rods and anaerobes
For pseudomonas infections, given along with aminioglycoside
Given parenterally
Reserve drugs: used only when other antibiotics not effective
**DOC in the Rx of Enterobacter

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Cephalosporins

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MOA is siimilar to that of penicillins
All cephalosporins are bactericidal
Less susceptible to inactivation by penicillinases

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First Generation Cephalosporins

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Cefazolin (parenteral), cephalexin (oral),
Active against Gr positive cocci & Kelbsiella
E. coli and K. pneumoniae are sensitive
Minimal activity against Gr negative organisms
*No penetration into CSF no role in tx of meningitis
Used for surgical prophylaxis and Rx of infections caused by susceptible organisms

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Second Generation Cephalosporins

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Cefoxitin, Cefotetan, Cefaclor, Cefamandole & Cefuroxime
Have less activity against Gr positive than 1st generation
Have extended Gr negative coverage
Uses: Bacteroides fragilis (Cefoxitin, Cefotetan)
H. influenzae & M. catarrhlis (Cefaclor, Cefamandole & Cefuroxime)
Only Cefuroxime enters the CSF

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Third Generation Cephalosporins

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Ceftazidime, Cefoperazone, Cefotaxime, Ceftriaxone, Ceftizoxime
Increased activity against Gr negative
Good penetration into BBB (especially -ax) (except Cefoperazone & Cefixime)
Individual drugs posses good antipseudomonal activity (Cefoperazone, Ceftazidime)
B. fragilis (Ceftizoxime)

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in Rx of gonorrhea

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Ceftriaxone (parenteral) & Cefixime (oral)

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Rx for acute ottitis media

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Ceftriaxone

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treatment of meningitis

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Cefotaxime, Ceftriaxone penetrates the CNS Remember AX to head

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Fourth Generation Cephalosporins

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Cefepime, Cefpirome
More resistant to inactivation by beta lactamases
Excellent penetration into gram negative bacteria
Much wider spectrum than 3rd generation (both Gr positive and Gr negative)

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ADR Cephalosporins

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Allergic reactions (skin rash to anaphylaxis)
Less frequent with cephalosporins when compared with penicillins
Cross-hypersensitivity between cephalosporins completely possible
Cross-reaction between penicillins is incomplete, but caution still needed
*History of anaphylaxis (life threatening) to penicillin is a contraindication for cephalosporin
Superinfection  C. Diff

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Vancomycin

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only use when bacteria changed PBP
-binds to D-Ala-D-Ala terminal, prvents peptydolgycan chain elongation
-MUST be IV
Narrow spectrum, lots of side effects
-only used when if bacteria changed PBP site- HAS TO STATE THIS in Q, therefore used in MRSA MRSE

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Vancomycin Resistance

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Occurs in strains of enterococci and staphylococci (VRE and VRSA)
Resistance involves a decreased affinity of vancomycin for the binding site
This is because of replacement of the terminal D-Ala by D-Lactate

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Red-Man Syndrome

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VancomycinAdverse Effects

related to RATE of intravenous infusion; should be infused over at least 60 minutes
resolves spontaneously after discontinuation
may lengthen infusion (over 2 to 3 hours) or pretreat with antihistamines in some cases

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Bacitracin

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Marked nephrotoxicity
No more used for oral therapy
Acts by inhibiting cell wall synthesis
Used topically for its antibacterial property

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Cycloserine

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exclusively to treat tuberculosis caused by strains of M tuberculosis resistant to first-line agents

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Rx of MRSA -

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vancomycin

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Rx of C. difficile

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- metro or vancomycin

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Rx of acute ottitis media –

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ceftriaxone single dose

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Rx of Meningitis –

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ceftriaxone, Cefotaxime

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Rx of Pseudomonas -

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Cefoperazone, Ceftazidime