Antibiotics 2 Flashcards
What is amoxycillin good for?
Gram negative bacteria
What is the problem with using amoxycillin?
It is susceptible to beta lactamases
How is amoxycillin’s weakness to beta lactamases countered?
By combining it with clavulanic acid in augmentin
Why is cephalexin prescribed for S. aureus?
Because it is good against gram positive
Can cephalexin function adequately in gram negatives?
Yes, unless they produce beta lactamases cephalosporinases
What is nitrofuran?
An antibiotic used against UTIs.
Why is nitrofuran only used for UTIs?
It has almost no tissue penetration but passes through urine if renal function is normal
Why is nitrofurantoin avoided in elderly?
Their kidneys are often not good at concentrating the antibiotic enough.
If people are on it it can cause pulmonary fibrosis
When is trimethoprim used alone?
Only in the cause of treating UTIs
What is trimethoprim commonly used with?
Sulphamethoxazole
What are the only oral antibiotics that can treat pseudomonas aeruginosa?
Norfloxacin and ciprofloxacin
What is norflaxacin?
A quinolone antibiotic
Why is norfloxacin not used to treat the UTI in the old lady’s case study?
It is of the few drugs that can treat pseudomonas so it would be a waste if it was used against E.coli
How is pseudomonas aeruginosa so good at resisting antibiotics?
It has active efflux mechanisms for beta lactams
It has reduced ingress of antibiotics like imipenem and aminoglycosides
It destroys antibiotic beta lactamases
PBPs and DNA gyrases with low affinity for beta lactams and quinolones
Which beta lactam antibiotic is effective against pseudomonas?
Piperacillin (Found and used as tazocin)
What cephalosporins are used to treat pseudomonas aeruginosa infections?
Cefepime
Ceftazidime
What carbapenems are used against pseudomonas aeruginosa and when?
They are last resort drugs. The ones typically used for pseudomonas are:
imipenem
meropenem
What carbapenems are commonly used but not effective against pseudomonas aeruginosa?
Ertepenem (No activity against pseudomonas aeruginosa)
Which monobactams work against pseudomonas?
Aztreonam
Which aminoglycosides work against pseudomonas aeruginosa?
Gentamicin
Tobramicin
Which quinolones work against pseudomonas bacteria?
Norfloxacin
Ciprofloxacin
Moxifloxacin
Why must damage be taken when using aminoglycosides?
They can damage kidneys
Can damage hearing
Will anti-pseudomonas drugs always be effective?
No some strains develop resistance
What are common causes of pneumonia?
Streptococcus pneumonia
Staph aureus
Enterobacteriaceae
Pseudomonas aeruginosa
Acinetobacter
Stenotrophomonas
What are the generations of cephalosoprins based on?
How long they’ve been around and spectrum + activity
What are some the 1st generation cephalosporins?
Cephalexin
Cefazolin
What are the 2nd generation cephalosporins?
cefaclor
cefamandole
Cefuroxime
What are the 3rd generation cephalosporins?
Cefotaxime
Ceftriaxone
Ceftaziidime
What is the 4th generation cephalosporin?
Cefepime
What is the newest cephalosporin?
Ceftaroline
What is the spectrum of 1st gen cephalosporins?
S. aureus streptococci
Strep
(some Enterobacteriaceae)
What is the spectrum of 2nd gen cephalosporins?
S. aureus
Strep
E. bacteriaceae
H. influenzae
What is the spectrum of 3rd gen cephalosporins?
E’bacteriaceae
strep
H.influenzae
P. aeruginosa (ceftazidime)
What is the spectrum of 4th gen cephalosporins?
E'bacteriaceae S.aureus Strep H.influenzae P.aeruginosa
What is the spectrum of 5th gen cephalosporins?
S. aureus (inc. MRSA)
strep
H.influenzae
E’bacteriaceae
What are enterococci always resistant to?
cephalosporins
What are the 2 types of beta-lactamase mediated resistance?
ampC beta-lactamase production
Extended spectrum beta-lactamase (ESBL) production
Where is the gene for ampC beta-lactamase located?
On a chromosome; it is normally repressed but inducers can result in its in production.
Which generation is most commonly destroyed by ampC beta-lactamase production?
3rd generation
What are inducers in the case of ampC?
Other antibiotics which may or may not be susceptible to destruction by ampC cephalosporinase.
What can a mutation in the ampC beta-lactamase gene result in?
It can cause the ampC beta-lactamase to be de-repressed stably.
Why is ampC beta-lactamase a problem if it is repressed?
These cephalosporinases destroy 3rd generation cephalosporins and so the mutation is selected for
Which bacteria are capable of ampC beta-lactamase production?
Enterobacter Serratia Citrobacter freundii Acinetobacter Proteus vulgaris and providencia Pseudomonas aeruginosa Morganella
What is ESBL production?
Production of Extended Spectrum beta-lactamases which are capable of destroying cephalosporins
Where were ESBL originally found?
Klebsiella
E.coli
Proteus mirabilis
Enterobacter
Citrobacter
What are ESBLs active against?
Older penicillins and cephalosporins
3rd gen cephalosporins
aztreonam
piperacillin
May carry unrelated genes conferring resistance to aminoglycosides and fluoroquinolones
How are gram negative rods that produce ampC beta-lactamase and ESBL treated?
ampC beta lactamase:
Carbapenems (meropenem)
4th gen cephalosporins
Aztreonam
Aminoglycosides
Quinolones
ESBL:
Carbapenems
4th gen cephalosporins
beta lactamase inhibitor combos
Aminoglycosides
Quinolones
What is happening to carbapenem effectiveness?
Carbapenemases are starting to show up nowadays in some bacteria making them resistant to them
What aminoglycosides are commonly used?
Gentamicin
Tobramycin (less commonly)
What are the main features of aminoglycosides?
They are older
Gentamicin is cheap
They are potent against enterobacteriaceae and P.aeruginosa
Also have activity against staphs and streps but not used as a first line therapy
They are very toxic
Often used with another agent
When is gentamicin used synergistically for strep infections?
In endocarditis it is used with peniciliin
What must be noted about aminoglycoside toxicity?
They are toxic to the ear (ototoxic)
Nephrotoxic (use very cautiously in renal failure)
Dose must be very calculated
Blood levels must be monitored at all times
What do petechial lesions on conjunctivae and legs indicate?
Neisseria meningitidis
What is the empirical antibiotic response for bacterial meningitidis?
Ceftriaxone (to cover neisseria meningitidis, streptococcus pneumoniae, and haemophilus influenzae)
Which gram positive meningitis causing bacteria is high in resistance often to ceftriaxone?
Strep pneumoniae
Can N.meningitidis be transmitted without showing symtpoms?
Yes
What drugs are used for prophylaxes for families of people who have recently recovered from neisseria meningitidis?
One dose of ciprofloxacin (adults)
2 doses of rifampicin (children)
ceftriaxone single IM injection in pregnant women
Does penicillin eradicate carrier state?
No
