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37 Cards in this Set
- Front
- Back
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what are the features of the B lactam antibiotics?
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all have 4 member B lactam ring
inhibit cell wall synthesis (bactericidal) |
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what are the pharmacokinetics of B lactam agents?
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vary in oral bioavailability
polar -> not metabolised extensively excreted unchanged in urine via glomerular filtration & tubular secretion (inhibited by probenicid) t1/2 30min -1hr except IM which are slow release only cross BBB when meninges inflamed |
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which penicillins have hepatic excretion?
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nafcillin (bile)
ampicillin (enterohepatic cycling) |
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what is the mechanism of penicillin action?
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bind to penicillin binding proteins in bacterial cytoplasmic membrane
inhibit transpeptidation reaction involved in cell wall cross linking activates autolytic enzymes -> cell wall lesions |
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how can bacteria be resistant to B lactams?
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B lactamase aka penicillinase
structural change in PBPs change in porin structure preventing access to PBP (eg pseudomonas & some gram -ve rods) |
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which bacteria have B lactamases?
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most staphs & many gram -ves
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which drugs are used to overcome B lactamase activities?
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clavulanic acid
sulbactam tazobactam |
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what are the narrow spectrum penicillinase susceptible penicillins?
when do we use them? |
pen G - syphilis/strep/meningococci
many are now resistant eg gono |
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what are the narrow spectrum penicillinase resistant drugs?
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methicillin (nephrotoxic)
nafcillin oxacillin |
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what is the downside of using methicillin?
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nephrotoxic
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what are the most commonly used wide spectrum penicillinase susceptible drugs? when are they used? what enhances them?
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amp/amoxycillin
gram +ve bacilli - strep, meningococcal, spirochaetes plus enterococci, e.coli, listeria, proteus, H influenze, moxarella enhanced when used w penicillinase inhibitor eg clav acid |
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what are the less commonly used wide spectrum penicillins? when are they used? what increases their efficacy?
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piperacillin, ticarcicillin
used for gram -ve rods (pseudomonas, enterobacter, some klebsiella) synergistic w aminoglycosides often need B lactamase inhibitor |
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what are the manifestations of penicillin allergy?
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urticaria, pruritis, fever, joint swelling, haemolytic anaemia, nephritis, anaphylaxis
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what percent of those with a history of penicillin reaction will develop one later?
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5-10%
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what complication of ampicillin is not an allergic reaction?
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maculopapular rash
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what are the complications of methicillin & nafcillin
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methicillin - interstitial nephritis
nafcillin - neutropaenia |
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what features of penicillin therapy can cause GI upset?
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ampicillin especially causes nausea & diarrhoea
yeasts from overgrowth pseudomonas colitis (from amp) |
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what is the structural similarity between cephalosporins & penicillin?
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b lactam ring
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what is the pharmacokinetics of cephalosporins?
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some available orally but most used parenterally
big side chains -> hepatic metaboism (ceftriaxone -> bile) but mainly renal elimination via active tubular secretion 1 and 2 gen don't enter meninges even when inflamed |
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how does cephalosporin susceptibility to B lactamases differ from penicillins?
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structurally different so less susceptible to staph penicillinases but inactivated by penicillinases of other bacteria
MRSA also cephalosporin resistant |
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what are the first generation cephalosporins? when do they work & when do they not work?
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cephalexin, cefazolin
active against Gram +ve cocci, many E coli & Klebsiella also don't work against gram -ve cocci, MRSA, most gram -ve rods |
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how do second generation cephalosporins compare to first generation?
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less gram +ve but more gram -ve activity
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give 3 examples of 2nd gen cephalosporins & the bugs they treat
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cefoxitin - anaerobic Bacteriodes fragilis
cefuroxime/cefaclor - sinus/ear/respiratory caused by H influenzae or M catarrhalis |
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what characterises the 3rd gen cephalosporins?
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increased activity against gram -ves resistant to other B lactams
able to penetrate BBB |
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when should 3rd generation drugs be used?
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in serious infections
except for gonorrhoea &OM when a single injection can substitute for a long oral course |
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what is cefepime & what are its features?
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4th generation ceph, more resistant to B lactamases incl effect against enterobacter, haemophilis, neisseria, some penicillin resistant pneumococci
has gram +ve activity of gen 1 with gram -ve activity of gen 3 |
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what is the frequency of cross reactivity with penicillin & cephalosporin?
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5-10%
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what effect does cephalosporins have on aminoglycosides?
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may increase nephrotoxicity when administered together
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what is aztreonam?
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a beta lactam drug resistant to betalactamases produced by some gram -ve rods (Klebsiella, pseudomonas, serratia), nil gram +ve activity
IV admin, eliminated by renal tubules |
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what are the carbapenems?
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imipenem, meropenem, ertapenem
chemically different from penicillins but retain b lactam structure "drug of choice" for enterobacter wide activity against gram +ve cocci, gram -ve rods & anaerobes can be used against pseudomonas w aminoglycoside |
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what must imipenem be given with & why?
how does meropenem differ |
cilastatin which inhibits the renal enzyme that deactivates it. cilastatin increases its half life and prevents a potentially nephrotoxic metabolite from forming
meropenem is exempt from this renal enzyme |
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when are the beta lactamase inhibitors active? when are they least active?
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most active - plasmid encoded b lactamases eg gono, strep, ecoli, H inf
least active - inducible chromosomal B lactamase eg enterobacter, pseudomonas, serratia |
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how does vancomycin work?
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inhibits transglycosylase, prevents cross linking of cell wall -> bactericidal
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what pharmacokinetic feature of vancomycin means it can be used for bacterial enterocolitis?
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not absorbed from GI tract so can be given orally
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what are the pharmacokinetics of vancomycin?
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penetrates most tissues & eliminated unchanged in urine
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what is "red man syndrome" & what are other side effects seen with the drug involved?
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diffuse flushing from histamine release after vancomycin use
other toxic vanc effects - chills, fever, phlebitis, oto & nephrotoxicity |
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how do the stages of cell wall synthesis differ as targets for penicillins, cephalosporins & vancomycins?
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penicillins/cephalosporins bind at transpepidation (final) stage to inhibit peptidoglycan cross linking
vancomycin inhibits transglycosylase, preventing elongation of peptidoglycan chains |
