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

ON

SNH

COOH

CH3

CH3

C

O

Isoxazoyl Penicillins

O

N

CH3

R1

R2

R1 R2

Oxacillin H HCloxacillin Cl HDicloxacillin Cl Cl

If chemical modification can overcome B-lactamase activity

Maybe chemical modification can also increase spectrum of activity ?

ON

SNH

COOH

CH3

CH3

C

ONH2

Ampicillin

Aminopenicillins

- Modified to broaden their spectrum of activity- better binding affinity to the PBP’s of

Enterococci ListeriaSome 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)

Amino-Penicillin

• Amoxicillin

• Ampicillin

• Bacampicillin

First penicillins discovered to be active against gram negative rods like E. coli and H. Influenzae.

Amino-Penicillin

• Same coverage like Pen VK plus:

- Listeria monocytogenes

- Enterococcus

- Proteus mirabilus

- E coli

- H. flu

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.

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.

Maybe if we change its structure a lot…..

…we will get even more gram negative coverage !

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

Ureidopenicillins

- similar to Ampicillin wrt Streptococcal activityEnterococcal 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)

ON

SNH

COOH

CH3

CH3

C

O

Penicillin G

ON

SNH

COOH

CH3

CH3

C

O

Piperacillin

NHNN

CH3

O O

C

O

5 Classes of Penicillins

Natural PenicillinsPenicillin G / Penicillin V

Penicillinase Resistant PenicillinsMethicillinNafcillinIsoxazoly Penicillins (Cloxacillin / Dicloxacillin / Oxacillin / Flucloxacillin)

AminopenicillinsAmpicillin / Amoxicillin

CarboxypenicillinsTicarcillin

UreidopenicillinsPiperacillin / Mezlocillin / Azlocillin

B-lactamases

Chromosomal Plasmid

Inducible Constituitive

High [ ] High [ ] Low [ ]

TEM 1-27SHV 1-8OXA 1-3PSE 1-5

Can NOT be overcome by Can be overcome byB-lactam – B-lactamase Inhibitor B-lactam – B-lactamase InhibitorCombinations Combinations

SPACESerratiaPseudomonasAcintobacterCitrobacterEnterobacter

Antibiotics

Biosynthetic Chemical

Penicillin(1945)

Antibiotics

Biosynthetic Chemical

Penicillin(1945)

Chemical ModificationSearch for otherCompounds

We like to think we are smart

Chemical Manipulation

Nature has been doing chemical modifications for millions of years

Bacteria have been fighting each other since before we evolved

There have been many chemical modifications

ON

SR

COOH

CH3

CH3

B-lactam

ON

SR

COOH

CH3

CH3

ON

CR

COOH

CH3

CH3

B-lactamCarbepenem

Carbapenems

1st isolated from Streptomyces cattleya in 1976

Base compound was thienamycin - methylene replacement for the Sulphur in the 5 membered ring

ON

SR

COOH

CH3

CH3

ON

CR

COOH

CH3

CH3

B-lactamCarbepenem

Carbapenems

- stable to B-lactamases

- due to the side chain being in a trans rather then the typical cis configuration seen in B-lactams

ON

S

ON

B-lactam Carbapenem

R R

2 Compounds in clinical use :

ImipenemMeropenem

Imipenem Meropenem

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

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 imipenem2. Loss of an outer membrane protein that would otherwise facilitate entry

ON

SR

COOH

CH3

CH3

PenicillinO

N

SR

COOH

CH3

CH3

ON

CR

COOH

CH3

CH3

O

R

N

S

COOH

R

Carbapenem

Side ChainModifications

Cephalosporin

Cephalosporins

1940’s Cephalosporium acremonium was isolated from the seawaterAt 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 onlyCephalosporin N re-identified as a penicillinCephalosporin C foundation for current Cephalosporin family

Cephalosporin C

- B-lactam ring fused to a 6 membered dihyrdothiazine ring

Mechanism of Action

Binds to PBP’s and interferes with synthesis of the peptidoglycancell 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

Gram –ve Gram +ve

LPS

Peptidoglycan

Cell membrane

Cell Memebrane

Cell Wall

Lipopolysaccharide (LPS)

PBP’s

B-Lactamases

Mechanisms of Resistance

1. Alteration of the PBP target2. Production of B-lactamases that inactivate cephalosporins

(Cephalinosporinases)3. Decreased ability of the Antibiotic to reach its target

(LPS of gram –ve bacteria)

Decreased affinity of PBP’s to bind cephalosporins are seen in

1. Streptococcus pneumoniae2. Haemophilus influenzae3. Neisseria gonorrhea4. MRSA

Major mechanism of resistance in gram +ve bacteria

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 plasmidsCan be constitutive or inducible

Effectiveness depends onAffinity of the Cephalosporinase for the CephalosporinConcentration of the Cephalosporinase producedConcentration of the Cephalosporin present

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)

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

0102030405060708090

100

1stGeneration

2ndGeneration

3rdGeneration

4thGeneration

Gram +veGram -veAnaerobic

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 GenerationCefotaxime (Claforan) IV 1.0 hrs 130 35 5.6-44Ceftriaxone (Rocephin) IV 8 hrs 250 90 1.2-39Ceftizoxime (Cefizox) IV 1.7 hrs 1330 30 0.5-29Ceftazidime (Fortaz) IV 1.8 hrs 160 17 0.5-30

4th GenerationCefepime (Maxipime) IV 2.1 hrs 130 20 3.3-5.7

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

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

3rd Generation Half Life Peak Protein CSF [ ] Bound Penetration

Cefotaxime (Claforan) IV 1.0 hrs 130 35 5.6-44Ceftriaxone (Rocephin) IV 8 hrs 250 90 1.2-39Ceftizoxime (Cefizox) IV 1.7 hrs 1330 30 0.5-29Ceftazidime (Fortaz) IV 1.8 hrs 160 17 0.5-30Cefixime (Suprax) po 3.5 hrs

Cefotaxime

Ceftriaxone

ON

SR

COOH

CH3

CH3

PenicillinO

N

SR

COOH

CH3

CH3

ON

CR

COOH

CH3

CH3

O

R

N

S

COOH

R

Carbapenem

Side ChainModifications

Cephalosporin

ON

SR

COOH

CH3

CH3

PenicillinO

N

SR

COOH

CH3

CH3

ON

CR

COOH

CH3

CH3

O

R

N

S

COOH

R

Carbapenem

Side ChainModifications

Cephalosporin

Monobactam

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 ofPseudomonas cepaciaXanthomonas maltophiliaAcinitobacterKlebsiella oxytocaHaemophilus

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 thuscan be used in Pen/Ceph allergic patients

Aztrenoam

-monobactam in clinical use

Limited to Gram –ve infections only

Penicillins

Carbepenems

Monobactams

Cephalosporins

B-lactamase Inhibitors

StructuralOverview

Antibiotics

Biosynthetic Chemical

Penicillin(1945)

Chemical ModificationSearch for otherCompounds

Antibiotics

Biosynthetic Chemical

Penicillin(1945)

Chemical ModificationSearch for otherCompounds

B-lactam AntibioticsDifferent Mechanisms

CarbapenemsMonobactamsCephalosporins

Glycopeptides

Glycopeptides

1st compound was isolated fromStreptomyces orientalis in 1956(bacteria)

Complex structure- amino acids + sugars

Vancomycin

Mechanism of Action :

Inhibit cell wall synthesis

- binds to peptidoglycan precursors

- blocks additional polymer extension

N-acetylglucosamine

N-acetylmuramic acid

d-ala

L-glu

Lys

d-ala

d-alaCell membrane

Cellwall

Transpeptidases (PBP’s)

N-acetylglucosamine

N-acetylmuramic acid

d-ala

L-glu

Lys

d-ala

d-ala

N-acetylglucosamine

N-acetylmuramic acid

d-ala

L-glu

Lys

d-ala

d-ala

N-acetylglucosamine

N-acetylmuramic acid

d-ala

L-glu

Lys

d-ala

d-ala

N-acetylglucosamine

N-acetylmuramic acid

d-ala

L-glu

Lys

d-ala

d-ala

N-acetylglucosamine

N-acetylmuramic acid

d-ala

L-glu

Lys

d-ala

d-ala

N-acetylglucosamine

N-acetylmuramic acid

d-ala

L-glu

Lys

d-ala

d-ala

N-acetylglucosamine

N-acetylmuramic acid

d-ala

L-glu

Lys

d-ala

d-ala

Mechanism of actionof Vancomycin

Vancomycin blocks cell wall synthesisBy binding to the d-alanyl-d-alanine site on the growing peptidoglycan chain

Vancomycin

Useful drug to treat B-lactam resistant staphylococcus aureus

Staphylococcus aureus

No b-lactamase B-lactamase Alter PBP’s

Penicillin Cloxacillin Vancomycin

(Penicillinase)

(MRSA)

Vancomycin

Useful drug to treat B-lactam resistant enterococcus

Enterococcus species

No b-lactamase B-lactamase Alter PBP’s

Ampicillin Vancomycin

Resistance to Vancomycin

1. Change in d-alanyl-d-alanine precursors - Van A, B, C mutations of VRE

2. Excess cell wall production- VISA

3. Biofilm production- seen on prosthetic devices /foreign bodies- Biofilms produced by bacteria impair the penetration of

the glycopeptide to the bacterial cells

4. Gram negatives constitutively resistant (LPS)

N-acetylglucosamine

N-acetylmuramic acid

d-ala

L-glu

Lys

d-ala

d-alaCell membrane

Cellwall

Transpeptidases (PBP’s)

d-lactate

N-acetylglucosamine

N-acetylmuramic acid

d-ala

L-glu

Lys

d-ala

d-lactate

Mechanism of resistance to Vancomycin

VRE Gene Complex

Van H gene- synthesizes d-lactate

Van A gene- binds d-lactate to d-alanine

Van X gene- hydrolyzes d-ala-d-ala

Van R & S genes- regulatory gene regions

Van Y& Z genes- accessory proteins

Antibiotics

Biosynthetic Chemical

Penicillin (1945)

Chemical modificationSearch for similar compounds

Antibiotics

Biosynthetic Chemical

B-lactam based antibiotics- Penicillins- Carbapenems- Monobactams- Cephalosporins

Antibiotics

Biosynthetic Chemical

B-lactam based antibiotics- Penicillins- Carbapenems- Monobactams- Cephalosporins

Vancomycin (1956)

Chemical modificationSearch for similar compounds

Naturally occuring glycopeptides

Vancomycin Streptomyces orientalis

Teicoplanin (Targocid) Actinoplanes teichomyceticus

Daptomycin (Cubicin) Streptomyces roseosporus

Ramoplanin Actinoplanes ATCC 33076

Semisythetic glycopeptides (2nd Generation)

Oritavancin Dalbavancin Telavancin

Glycopeptide Antibiotics

Glycopepetides Lipopeptides Lipoglycopeptides

Daptomycin(Cubicin)

(LY146032)

VancomycinTeicoplanin

Ramoplanin

Oritavancin (LY33328)

Dalbavancin

Telavancin

Inhibition of cell wall synthesis+

Increase cell membrane permeability

Inhibition of cell wall synthesisCidal

Semisynthetic derivatives

Teicoplanin Dalbavancin

Vancomycin Oritavancin

Role of the newer glycopeptide antibiotics….

Combat emerging resistance of

MRSA

VRE

Biosynthetic Antibiotics that inhibit protein synthesis

Aminoglycosides1943

Macrolides1952 Tetracyclines

1953

Lincosamides1962

Stretpogramins1953