Antimicrobials: Cell Wall Synthesis Inhibitors: All but penicillins Flashcards Preview

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Flashcards in Antimicrobials: Cell Wall Synthesis Inhibitors: All but penicillins Deck (36):

Moving on to the next class of cell wall synthesis inhibitors are the cephalosporins. All cephalosporins are considered inactive against what bacteria?



Cephalosporins are divided into generations. There are five generations. Starting with first generation cephalosporins are Cefazolin and Cephalexin, what are some features of these drugs?

Cefazolin (IV)
Cephalexin (oral)
--both active against gram + cocci (including staph and strep) (many strains of E.coli, P. mirabilis, and Klebsiella are sensitive)
Good penicillin G substitutes
Used for tx of infections due to sensitive bacteria
Rarely the drug of choice for any infections but oral drugs may be used for tx of UTIs or staph/strep skin infections


The major use of cefazolin (1st generation) is for what?

Surgical Prophylaxis (due to the long half life)


Moving on to the second generation cephalosporins. They include Cefaclor, Cefoxitin, Cefotetan and Cefamandole. What are some features?

Less active against gram + cocci but more active against gram - bacilli.
Clinical use: sinus, ear, and resp infections caused by H. influenzae and M. catarrhalis (cefamandole and cefaclor) and infections caused by the anaerobe bacteroides fragilis (Cefotetan and Cefoxitin)
Combo activity against aerobic and facultative gram negative bacilli plus bacteroides has led to the use of these drugs (cefotetan and cefoxitin) in the prophylaxis and therapy of infections in the abdominal and pelvic cavities.


The third generation cephalosporins are next. They include cefoperazone, cefotaxime, ceftazidime, ceftriaxone and cefixime. What are some features of these drugs?

Increased activity against gram - organisms
Resistant to other beta lactam drugs
Ability to penetrate the BBB
Active against: Enterobacteriacae (e.coli and p.mirabilis), neisseria and H.influenzae.
Less active against most gram + organisms than the first generation drugs and are inactive against enterococci, listeria, MRSA and Acinetobacter


Ceftriaxone is the drug of choice for the therapy of what?

Penicillin-resistant gonorrhea and meningitis due to ampicillin-resistant H. influenzae in children
Tx of lyme disease involving CNS, joints
Prophylaxis of meningitis in exposed individuals (including prego women)


Cefoperazone and Ceftazidime have activity against what?

P. aeruginosa


Drugs in third generation are usually reserved for what?

Tx of serious infections resistant to other drugs
Exceptions: tx of gonorrhea and in acute otitis media when a single injection of ceftriaxone is effective as a 10 day course of amoxicillin


Next are the fourth generation cephalosporins. Include: Cefepime. What are some features?

IV only
More resistant to beta lactamases produced by gram negative organisms including enterobacter, haemophilis, neisseria and some penicillin resistant pneumococci
Combines the activity of first generation agents with the wider gram negative spectrum of third generation drugs


Finally is the fifth generation cephalosporin: Ceftaroline. What are some features?

IV only
Binds to PBP2a (a penicillin binding protein encoded by methicillin resistant S. Aureus)
Inactive against P. aeruginosa, acinetobacter and B. fragilis
Useful in skin and soft tissue infections due to MRSA, particularly if gram - organisms are coinfecting
Tx of community acquired pneumonia when first line agents are not successful


Moving on to the pharmacokinetics, what is the administration of cephalosporins?

Most administered IV due to poor oral absorption
oral includes: cephalexin, cefaclor, and cefixime


What is the distribution of cephalosporins?

Most 1st and 2nd generation drugs do not enter the CSF even when the meninges are inflamed
Ceftriaxone is well distributed and crosses the BBB easily.


What is the excretion of cephalosporins?

Major route is renal
Cefoperazone and Ceftriaxone: bile (so you can give to a person in renal failure)


Moving on to adverse effects of cephalosporins, what is hypersensitivity?

Complete cross hypersensitivity between different cephalosporins should be assumed
--however if a patient has a mild penicillin allergy a cephalosporin should still be given


What are some other adverse effects of cephalosporins?

Pain at IM injection site
Drugs containing a methylthiotetrazole group may cause hypoprothrombinemia and disulfiram-like reactions
Ceftriaxone should not be used in pregnancy as it can cross the BBB and displaces bilirubin from binding sites leading to kernicterus


The next group of cell wall synthesis inhibitors are the Carbapenems (IV). what are some features of these drugs?

Imipenem and Meropenem
--low susceptibility to beta lactamases
Very broad spectrum of activity against Gram + cocci, Gram - rods, aerobes and anaerobes
Affective against pseudomonas


What infections are carbapenems used for?

Infections caused by organisms resistant to other antibiotics.
--not effective against MRSA
To reduce the risk of resistance their use is usually restricted to these types of multi-drug resistant infections


Carbapenems are the drug of choice for what?

For enterobacter infections and extended spectrum beta lactamase producing gram -
Used for surgical infection prophylaxis
Current Concern: resistant to the carbapenems by producing carbapenemases (ex. carbapenem-resistant enterobacteriaceae and carbapenem-resistant klebsiella)


What are the pharmacokinetics and adverse effects for Imipenem?

--rapidly inactivated by renal dehydropeptidase I to form a potentially nephrotoxic metabolite
--it is always administered in a fixed combo with cilastatin (an inhibitor enzyme)
--cilastatin increases the plasma half life of imipenem and inhibits formation of this metabolite
Adverse Effects:
--GI distress and at very high levels it can cause CNS toxicity


What are the pharmacokinetics and adverse effects for Meropenem?

--not metabolized by renal dehydropeptidases and does not have to be given with cilastatin
Adverse effects:
---is similar to imipenem apart from that it is less likely to cause seizures
Note the carbapenems have partial cross allergenicity with penicillins


Moving on to the next set of cell wall synthesis inhibitors are the Monobactams. What are some features?

--monocyclic beta lactam ring
Limited activity to aerobic gram - rods (pseudomonas)
Do not have activity against gram + bacteria or anaerobes
Resistant to the action of most beta lactamases


What is the main use of Aztreonam (monobactam)?

Tx of UTIs, LRTs, septicemia, skin/structure infections, intra-abdominal infections and gynecological infections caused by susceptible gram negative bacilli


What are the pharmacokinetics for Aztreonam?

Administered either IM or iV and penetrates well into the CSF when inflamed
--can also be given by inhalation to improve resp symptoms in cystic fibrosis with P. aeruginosa
Eliminated via renal tubular secretion thus its half life is prolonged in renal failure


What are the adverse effects for Aztreonam?

Non-toxic and penicillin-allergic patients tolerate it without reaction
--occasional skin rashes and elevation of serum aminotransferases, along with thrombophlebitis and pain at the injection


Next in the cell wall synthesis drugs is Vancomycin, what is the MOA and resistance?

Inhibits cell wall synthesis (At :d-ALA-d-ALA)
--inhibits the transglycosylase, preventing further elongation of peptidoglycan and cross linking
--both peptidoglycan and polymerization and cell wall synthesis are inhibited so lysis of cell
Enterococci resistance due to modification of the d-ALA-d-ALA binding site
--ALA is replaced by D-lactate resulting in vancomycin being unable to bind to its target.


What is the spectrum of activity and clinical applications of vancomycin?

Bactericidial: against Gram positive bacteria only
Needs to be given with aminoglycosides against enterococcus faecium and enterococcus faecalis strains that do not inhibit high levels of aminoglycogside resistance.
---this combo is first line choice for the treatment of enterococcal endocarditis


What are the main uses of Vancomycin?

Tx of serious infections caused by beta lactam resistant gram + organisms
Tx of infections caused by gram + organisms in individuals who have serious allergies to beta lactam agents


Vancomycin can be administered orally for the treatment of what?

Staphylococcal Enterocolitis
Antibiotic Associated pseudomembranous colitis


How is vancomycin administered?

Poorly absorbed from the GI tract so give IV
IV infusions must be given slowly (60-90min) to reduce infusion related adverse effects
--adequate penetration to the CSF only occurs when the meninges are inflamed
Drug excreted via kidneys so be careful in renal insufficiency this drug will accumulate


What are the adverse effects of vancomycin?

-most common phlebitis at site of injection with fever and chills
Red man or red neck syndrome: infusion related flushing of the face and upper torso caused by release of histamine (prevented by prolonging infusion time)
Ototoxicity and nephrotoxicity are rare: occurs when vancomycin is allowed to accumulate
If given with aminoglycoside the risk for ototoxic or nephrotoxic effects increases.


Moving on to the next cell wall synthesis inhibitor, Daptomycin. What is the MOA and resistance?

--developed to meet the need for drugs active against resistant organisms.
--bind to the cell wall membrane of sensitive bacteria via calcium dependent insertion of its lipid tail ----depolarization of the cell wall membrane with potassium efflux and rapid cell death


What is the spectrum of activity of Daptomycin?

It is active against vancomycin-resistant strains of enterococci and S. aureus
Inactive against gram - bacteria
Pulmonary surfactant antagonizes daptomycin and it should not be used for pneumonia


What is Daptomycin used for?

Tx of complicated skin and skin structure infections caused by susceptible aerobic gram + organisms, S. aureus bacteremia, including right sided native valve infective endocarditis caused by MSSA or MRSA
Tx: severe infections caused by MRSA or VRE


What are the pharmacokinetics and adverse effects for daptomycin?

---IV and can accumulate in patients with renal insufficiency
---constipation, myopathy and creatine phosphokinase levels should be monitored


The next cell wall synthesis bacteria is bacitracin, what are some feature?

Peptide abx: gram + microorganisms
Inhibits cell wall formation by interfering with dephosphorylation in cycling of the lipid carrier that transfers peptidoglycan subunits to the growing cell wall
--no cross resistance between bacitracin and other drugs
Very nephrotoxic when given systemically so only used for topical tx of mixed bacterial infections of the skin, wounds or mucus membranes


The last cell wall inhibitor is Fosfomycin what are some features?

Active against gram + and gram - organisms
Inhibits cytoplasmic enzyme enolpyruvate transferase (important in early stages of cell wall synthesis)
Given orally
Tx: of uncomplicated lower UTIs

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