Beta-Lactam Antibiotics & Other Cell Wall Synthesis Inhibitors Flashcards
what are the similarities of bactericidal and bacteriostatic?
they are both antimicrobial drugs
What are the differences of bactericidal ang bacteriostatic?
Bactericidal - eradicate infection without host defense mechanism
Bacteriostatic - inhibits antimicrobial growth, need host defense mechanism to eradicate infection
Drugs with structures containing a beta-lactam ring: includes the penicillins, cephalosporins and carbapenems. This ring must be intact for antimicrobial action
Beta-lactam
antibiotics
Bacterial enzymes (penicillinases, cephalosporinases) that hydrolyze the beta-lactam ring of certain penicillins and cephalosporins
Beta-lactamases
Potent inhibitors of some bacterial beta-lactamases used in combinations to protect hydrolyzable penicillins from inactivation
Beta-lactamase
inhibitors
Lowest concentration of antimicrobial drug capable of
inhibiting growth of an organism in a defined growth
medium
Minimal
inhibitory
concentration
(MIC)
Bacterial cytoplasmic membrane proteins that act as the initial receptors for penicillins and other beta-lactam antibiotics
Penicillin-binding
proteins (PBPs)
Chains of polysaccharides and polypeptides that are
cross-linked to form the bacterial cell wall
Peptidoglycan
More toxic to the invader than to the host; a property of
useful antimicrobial drugs
Selective
toxicity
Bacterial enzymes involved in the cross-linking of linear peptidoglycan chains, the final step in cell wall synthesis
Transpeptidase
Types of Microbial resistance:
1.Production of antibiotic-inactivating enzymes
2.Changes in the structure of target receptors
3.Increased efflux via drug transporters
4. Decreases in the permeability of microbes’ cellular membrane to antibiotics
Strategies to combat Microbial resistance
- Use of adjunctive agents that can protect against antibiotic inactivation
- Use of antibiotic combinations
- Introduction of new chemical derivatives of establish anibiotics
- Efforts to avoid indiscriminate use or misuse of anitbiotics
the major antibiotics that
inhibit bacterial cell wall synthesis:
- Penicillins
- Cephalosporins
Why are they called beta-lactams
Because of their 4-member ring
include some of the most
effective, widely used, and well-tolerated agents available for
the treatment of microbial infections.
beta-lactams
also inhibit cell wall synthesis but are not nearly as important as the beta-lactam drugs:
- Vancomycin
- Fosfomycin
- Bacitracin
The selective toxicity
of the drugs discussed in this chapter is mainly due to specific
actions on the _________ that is unique to the microorganism.
synthesis of a cellular structure
how many antibiotics that act as cell wall synthesis inhibitors are currently available, with individual
spectra of activity that afford a wide range of clinical applications
More than 50
2 types of Narrow spectrum Penicillins
- Penicillinase susceptible
- Penicillinase resistant
What generation is included in narrow spectrum cephalosporins?
1st generation
What generation is included in wider spectrum cephalosporins?
2nd, 3rd, 4th generation
3 miscellaneous Bacterial cell-wall inhibitors
- Carbapenems
- Aztreonam
- Vancomycin
Penicillins are derivatives of what?
6-aminopenicillanic acid
What does all penicillins contain that is esential for antibacterial activity
beta-lactam ring
Penicillin subclasses have additional chemical substituents that confer differences in:
- antimicrobial activity
- susceptability to acid and enzymatic hydrolysis
- biodisposition
Pharmacokinetics
Since penicillins vary in their resistance to gastric acid, therfore they vary in their __________
Oral Bioavailability
Pharmacokinetics
Why are penicillins not metabolized extensively?
because they are polar compounds
Pharmacokinetics
What are the penicillin parenteral formulations that are available for injections?
- Ampicillin
- Piperacillin
- Ticarcillin
Pharmacokinetics
Penicillins are usually unchange in the urine via:
- glomerular filtration
- tubular secretion
Pharmacokinetics
The tubular secretion of penicillins are inhibited by?
Probenecid
Pharmacokinetics
What kind of penicillin is mainly excreted in the bile?
Nafcillin
Pharmacokinetics
What kind of penicillin undergoes enterohepatic cycling?
ampicillin
Pharmacokinetics
Half life of most penicillins?
30 mins to 1 hour
Pharmacokinetics
Forms of penicillin G that are administered intramuscularly and have longer half lives
- procaine
- benzathine
Pharmacokinetics
Why do procaine and benzathine have longer plasma half-lifes?
because the active drug is released vrey slowly to the bloodstream
Pharmacokinetics
When does most penicillins cross the blood-brain barrier?
When the meniges are inflamed
Mechanisms of Action
What kind of drugs are beta-lactams?
Batericidal drugs
Mechanisms of Action
Steps on how beta-lactams inhibit cell wall synthesis:
- Bind to specific receptors (penicillin-binding proteins)
- Inhibition of transpeptidation reaction
- Activation of autolytic enzymes
Mechanisms of Action
Where are PBPs located?
in the bacterial cytoplasmic membrane
Mechanisms of Action
the reaction that cross-links the linear pe[tidoglycan chain constituents of the cell wall
Transpeptidation reaction
Mechanisms of Action
Enzymes that causes lesions in the bacterial cell wall
Autolytic enzymes
Resistance
If this happens to the beta-lactam ring, it will result in the loss of antibacterial activity
Enzymatic hydrolysis
Resistance
Is the major mechanism of bacterial resistance
Formation of beta-lactamase (penicillinase)
Resistance
What organisms use the formation of penicillinase as resistance?
- staphylococci
- gram negative organisms
Resistance
What inhibitors of penicillinase are often used in combination with penicillin to prevent their inactivation?
- cluvanic acid
- sulbactam
- tazobactam
Resistance
Structural change in target PBPs of staphylococci is responsible for?
methicillin resitance
Resistance
Structural change in target PBPs of pneumococci and enterococci is responsible for?
penicillin G resistance
Resistance
Example of pneumonococci
Penicillin resistant Streptococcus pneumoniae (PRSP)
Resistance
What organisms use changes in the porin structure as resistance
Gram negative rods (Pseudomonas aeruginosa)
Resistance
changes in the porin structures in the outer cell wall membrane may contribute to resistance by what?
impeding access of penicillins to PBPs
Clinical Uses
Narrow-spectrum penicillinase-susceptible agents
- Penicillin G
- Penicillin V
Clinical Uses
the prototype of a subclass of penicillins that have a limited spectrum of antibacterial activity and are susceptible to beta-lactamases.
Penicillin G
Clinical Uses
Penicillin G theraphy of infections include?
- common streptococci
- miningcocci
- gram-positive bacilli
- spirochetes
Clinical Uses
Strains of pneumococci that are now resistant to penicillins
Penicillin resistant S. pneumoniae (PRSP)
Clinical Uses
Strains that are resistant to penicillin via beta-lactamase:
- Stapphylococcus aureus
- Neisseria gonorrhoeae
Clinical Uses
Penicillin G is the suitable drug for?
Syphilis
Clinical Uses
Penicillin G is not the suitable drug for?
gonorrhea
Clinical Uses
Activity of penicillin G against enterococci is enhanced by?
coadministration of aminoglycosides
Clinical Uses
oral drug mainly used in oropharyngeal infections
Penicillin V
Clinical Uses
Very-narrow-spectrum penicillinase-resistant drugs:
- methicillin
- nafcillin
- oxacillin
Clinical Uses
Very-narrow-spectrum penicillinase-resistant drug that is a prototype but rarely used because of its nephrotoxic potential
methicillin
Clinical Uses
The primary use of Very-narrow-spectrum penicillinase-resistant drugs is in the treatment of known or suspected _________
staphylococcal infections
Clinical Uses
are resistant to all penicillins and are often resistant to multiple antimicrobial drugs.
Methicillin-resistant (MR)
staphylococci
- S. aureus (MRSA)
- S. epidermis (MRSE)
Clinical Uses
Wider-spectrum penicillinase-susceptible drugs:
- Ampicillin and Amoxicillin
- Piperacillin and Ticarrcillin
Clinical Uses
Ampicillin and amoxicillin therapy of infections include?
- similar to penicillin G
- enterococci
- Listeria monocytogenes
- Escherichia coli
- Proteus mirabilis
- Haemophilus influenzae
- Moraxella catarrhalis
Clinical Uses
Piperacillin and ticarcillin have activity
against:
gram-negative rods
- Pseudomonas
- Enterobacter
- Klebsiella sps
Clinical Uses
Most drugs in this subgroup have synergistic actions with aminoglycosides against such organisms.
Piperacillin and ticarcillin
Clinical Uses
What penicillinase inhibitors are used with piperacillin and ticarcillin to ennhance their activity?
- tazobactam
- clavulanic acid
Toxicity
Allergic reactions to penicillin include:
- urticaria
- severe pruritus
- fever
- joint swelling
- hemolytic anemia
- nephritis
- anaphylaxis
Toxicity
How many percent of people with history of penicillin reaction have a allergic response when given penicillin again?
5-10%
Toxicity
Methicilin causes?
interstitial nephritis
Toxicity
nafcillin is associated with?
neutropenia
Toxicity
Ampicillin frequently causes?
maculopapular skin rash
Toxicity
What are the antigenic determinants that causes allergic reactions to penicillin
Penicilloic acid
Toxicity
Degration product of penicillin
penicilloic acid
Toxicity
occur with oral penicillins, especially with ampicillin.
Nausea and diarrhea
Toxicity
Toxicity of penicillins:
- Allergy
- Gastrointestinal disturbances
Toxicity
Gastrointestinal upsets from penicillin may be caused by:
- direct irritation
- overgrowth of gram + organisms or yeast
Toxicity
Ampicillin has been implicated in what disease?
pseudomembranous colitis
The cephalosporins are derivatives of what?
7-aminocephalosporanic acid
1st generation Cephalosporins
- cephalexin
- cefazolin
- cefadroxil
- cephalotin
- cephadrine
- cephapirin
2nd generation cephalosporins
- cefuroxime
- cefoxitin
- cefotetan
- cefamandole
- cefaclor
3rd generation cephalosporins
- ceftriazone
- cefotaxime
- cefoperazone
- ceftazidime
- cefixime
- cefnidir
- moxalactam
4th genaration cephalosporins
- cefepime
- ceftaroline
Pharmacokinetics
Several cephalosporins are administered via
oral
Pharmacokinetics
Most cephalosporin are administered via?
parenterally
Pharmacokinetics
Major elimination mechanism of cephalosporins?
renal exretion via active tubular secretion
Pharmacokinetics
What kind of elimination mechanism cephalosporins with side chains may undergo?
hepatic metabolism
Pharmacokinetics
Type of cephalosporin excreted mainly in the bile?
- cefoperazone
- ceftriazone
Pharmacokinetics
What generation of cephalosporins do not enter the cerebrospinal fluid even when the miniges are inflamed?
First and second generation
Resistance
Structural differences from penicillins render cephalosporins
less susceptible to penicillinases produced by __________
staphylococci
Resistance
Many bacteria are still resistant to cephalosporins through?
production of other beta-lactamase that can inactivate cephalosporins
Resistance
Resistance to cephalosporins can also resukt from:
- decrease of permeability to cephalosporins
- changes in PBPs
Resistance
Are Methicillin-resistant staphylococci resistant to cephalosporins?
yups
Clinical Uses
Cefazolin is administered via
parenteral
Clinical Uses
cephalexin is administered via?
oral
Clinical Uses
First generation drugs are active againts:
- Gram positive cocci (staphylococci and common streptococci)
- E. coli
- K. pneumoniae
Clinical Uses
Clinical uses of 1st generation drugs
- treatment of infection
- surgical prophylaxis (selected conditions)
Clinical Uses
First generation drugs have limited activity against:
- gram-negative cocci
- enterococci
- methicillin-resistant staphylococci
- gram negative rods
Clinical Uses
Drugs in this subgroup usually
have slightly less activity against gram-positive organisms than the first-generation drugs but have an extended gram-negative coverage.
Second-generation drugs
Clinical UsesClinical Uses
Second generation drugs that can treat infections caused by the anaerobe Bacteroides fragilis
- cefotetan
- cefoxitin
Clinical Uses
Second-generation drugs that can treat sinus, ear, and respiratory infection caused by H. influenzae or M catarrhaliss
- cefamandole
- cefuroxime
- cefaclor
Clinical Uses
Feature of this subgroup include increased activity against gram-negative organisms resistant to other beta-lactam drugs and ability to penetrate the blood-brain barrier
Third generation drugs
Clinical Uses
3rd generations drugs that cannot penetrate the blood-brain barrier
- cefoperazone
- cefixime
Clinical Uses
3rd generation drugs are active against:
- Providencia
- Serratia marcescens
- beta-lactamase producing strains (H. influenza and Neisseria)
Clinical Uses
3rd generation drugs are less active against?
Enterobacter strains that produce extended-spectrum beta-lactamases
Clinical Uses
Currently the most active cephalosporins against penicillin-resistant pneumonococci (PRSP strains)
but resistance is reported
Ceftriaxone and cefotaxime
Clinical Uses
3rd generation drugs that have activity against Pseudomonas
- cefoperazone
- ceftazidime
Clinical Uses
3rd generation drugs that have activity against B. fragilis
ceftizoxime
Clinical Uses
Drugs in this subclass should
usually be reserved for treatment of serious infections
3rd generation drugs
Clinical Uses
Ceftriaxone is adminstered via?
parenteral
Clinical Uses
cefixime is administered via?
oral
Clinical Uses
Drugs of choice for gonorrhea?
- ceftriaxone
- cefixime
Clinical Uses
In acute otitis media, a single injection of ceftriaxone is usually as effecetive as?
10-day course treatment of amoxicillin
Clinical Uses
Cefepime is more resistant to
beta-lactamases produced by gram-negative organism including:
- Enterobacter
- Haemophilus
- Neisseria
- penicillin-resistant pneumococci
Clinical Uses
combines the gram-positive
activity of first-generation agents with the wider gram-negative spectrum of third-generation cephalosporins
Cefepime
Clinical Uses
has activity in infections caused by methicillin-resistant staphylococci.
Ceftaroline
Toxicity
Allergic reaction of cephalosporins:
- skin rashes
- anaphylactic shock
Allergic reactions occur less frequently in penicillins than with cephalosporins
that is not factual
Does complete cross-hypersensitivy exist in different cephalosporins
yups
Does complete cross-reactivty exist between penicillins and cephalosporins?
nope
Should patients with history of anaphylaxis to penicillins be treated with cephalosporins?
no way
Cephalosporins may cause pain
at __________
intramuscular injection sites
Cephalosporins may cause _______ after intravenous administration
phlebitis
What will happen if you administer cephalosporin with aminoglycosides?
increase nephrotoxicity
may cause hypoprothrombinemia and disulfiram-like reactions with ethanol.
Drugs containing a methylthiotetrazole group
- cefamandole
- cefoperazone
- cefotetan
Is a monobactam that is resistant to beta-lactamases produced by certain gram-negative rods
Aztreonam
What are the certain gram negative rods that aztreonam are resistant to
- Klebsiella
- Pseudomonas
- Serratia
Aztreonams have no activity against?
Gram-positive bacteria or anaerobes
Where does aztreonam prefer to bind?
PBP3
Aztreonam are synergistic with what?
Aminoglycosides
Aztreonam is administered via?
IV
Aztreonam is eliminated via?
Renal tubular secretion
Aztreonam’s half life is prolonged in what situation?
Renal failure
Adverse effects of aztreonam:
- gastrointestinal upset with possible superinfection
- vertigo
- headache
- hepatoxicity (rare)
Can Skin rash occur in aztreonam?
Yeah
Cross-allergenity of aztreonam with penicillin is possible?
Nope
Examples of carbapenems
- imipenem
- doripenem
- meropenem
- ertapenem
Drugs that are chemically different from penicillins but retaining the betalactam ring structure with low susceptanility to beta-lactamases
Carbapenems
Carbapenems have wide activity against:
- gram-positive cocci (penicillin resistant pneumococci)
- gram-negative rods
- anerobes
Carbapenems are used in combination with what in pseudomonal infections
Aminoglycosides
Carbapenems are administered via?
Parenterally
Drugs that are useful for infections caused by organisms resistant to other antibiotics
Carbapenems
Organisms that are resistant to carbapenems
MRSA strains of staphylococci
Carbapenems are currently co-drugs of choice for infections caused by:
- enterobacter
- citrobacter
- serratia
Imipenem is rapidly inactivated by what?
Renal dehydropeptidase I
An inhibitor of the enzyme renal dehydropeptidase
Cilastatin
Imipinem is always administered with this
Cilastatin
Increases the half life of imipenem and inhibits the formation of a potentially nephrotoxic metabolite
Cilastetin
Adverse effects of imimpenem-cilastetin:
- gastrointestinal distress
- skin rash
- very high plasma levels
- cns toxicity (confusion, enchepalopathy, seizures)
Does Imipenem-cilastatin have partial allergenicity with penicillins
Yups
Is similae to imipenem except that it is not metabolized by renal dehydropeptidases and is less likey to cause seizures
Meropenem
Type of carbapenem that has a long half life but is less active against enterococci and Pseudomonas and its intramuscular injection causes pain and irritation
Ertapenem
Examples of beta-lactamase inhibitors
- clavulanic acid
- sulbactam
- tazobactam
Are used in fixed combinations with certain hydrolyzable penicillins
Beta-lactamase inhinbitors
Beta-lactamase inhibitors are most active against:
Plasmid-encoded beta-lactamase produced by:
- gonococci
- streptococci
- e. coli
- h. influenzae
Beta-lactamse inhibitors are not good inhibitors of what?
Inducible chromosomal beta-lactamases formed by
- enterobacter
- pseudomonas
- serratia
Is a bactericidal glycoprotein that binds to the D-Ala-D-Ala terminal of nascent peptidoglycan pentapeptide side chain
Vancomycin
Drug that inhibit transglycosylation
Vancomycin
Drug that prevents elongation of the peptidoglycan chain and interferes with cross linking
Vancomycin
Strains that are resistan to vancomycin
- vancomycin-resistant enterococci (VRE)
- vancomycin-resistant S. aureus
How does VRE and VRSA resist vancomycin?
Replacement of the terminal D-ala by D-lactate
Vancomycin are used for serious infections caused by?
Drug-resistant gram-positive organisms
- methicilin-resistan staphylococci (MRSA)
- penicillin-resistan pneumococci
- c. difficile
Vancomycins are used in combination with what for treatment if penicillin resistan pneumococci (PRSP)?
3rd generation cephalosporin (ceftriaxone)
Vancomycin is also a backup drug for treatment of infections caused by?
Clostridium difficile
Drugs that similar characteristics to vancomycin
Teicoplanin and telavancin
Vancomycin is not absorbed from the
Gastrointestinal tract
Vancomycin may be given orally for what disease?
Bacterial enterocolitis
When given this way, vancomycin penetrates most tissues and is eliminated unchanged in the urine
Parenterally
This mandatory in patients with renal impairment taking vancomycin
Dosage modification
Toxic effects of vancomycin:
- chills
- fever
- phlebitis
- ototoxicity
- nephrotoxicity
Rapid intavenous infusion of vancomycin may cause
Diffuse flushing (red man syndrome) from histamin release
Is an antimetabolite inhibitor of cytosolic enolpyruvate transferase
Fosfomycin
Prevent formation of N-acetylmuramic acid
Fosfomycin
An esential precursor molecule for peptidoglycan chain formation
N-acetylmuramic acid
Resistance to fosfomycin occurs via
Decreased intracellular acumulation of the drug
Fosfomycin is excreted via?
Kidney
Fosfomycin urinary levels exceed what for many urinary tract pathogens
Minimal inhibitory concentrations (MICs)
In a single dose, this drug is less effective than a 7-day course of treatment with flouriquinolones
Fosfomycin
With multiple dosing of this drug, resistance emerges rapidly and diarrhea is common
Fosfomycin
Fosfomycin may be synergistic with these drug in specific infections
Beta-lactam and quinolone antibiotics
Is a peptide antibiotic that interferes with a late stage in cell wall synthesis in gram-positive organisms
Bacitracin
Because of its marked nephrotoxicity, the drig is limited to topical use
Bacitracin
An antimetabolite that blocks the incorporation of D-ala into the pentapeptide side chain of peptidoglycan
Cycloserine
Bacause of its potential neurotoxicity, it is only used to treat tuberculosis caused by organisms resistant to first line antituberculosis drugs
Cycloserine
Is a novel cyclic lipopeptide with spectrum similar to vancomycin but active against vancomycin-resistant strains of enterococci and staphylococci
Daptomycin
Daptomycin is eliminated via
Kidney
This should be monitored since daptomycin may cause myopathy
Creatine phosphokinase
CYLCOSERINE toxic effects
potential neurotoxicity
- tremors
- seizure
- psychosis