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77 Cards in this Set
- Front
- Back
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What organisms are penicillins active against? |
Gram positive organisms Gram negative cocci Non-beta-lactamase-producing anaerobes |
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What is the mechanism of action of penicillins? |
Inhibition of bacterial growth by interfering with the transpeptidation reaction of bacterial cell wall synthesis |
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What are the four mechanisms of resistance to beta-lactam antibiotics? |
1) inactivation of antibiotic by beta-lactamase 2) modification of target penicillin-binding proteins 3) impaired penetration of drug to target penicillin-binding proteins 4) antibiotic efflux |
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What is the distribution of penicillin? |
Diffuses rapidly into most tissues, with the exception of brain and CSF unless meninges are inflamed |
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How are penicillins excreted? |
Rapid renal excretion (mostly tubular secretion rather than glomerular filtration) |
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How is dicloxacillin excreted? |
Renal and hepatic (no dose adjustment required in renal failure) |
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How does probenecid increase blood levels of penicillins? |
Impairs renal tubular secretion |
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What are two commonly used 1st generation cephalosporins? |
1) cephalexin 2) cephazolin |
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Can cephazolin be used to treat meningitis? |
No, it does not penetrate the CNS |
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What are two commonly used 2nd generation cephalosporins? |
1) cefaclor 2) cefuroxime |
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What is the spectrum of 1st generation cephalosporins? |
Very active against gram-positive cocci, also some gram-negative cocci and anaerobic cocci |
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What is the spectrum of 2nd generation cephalosporins? |
Similar to 1st generation, with extended activity against gram-negative bacteria (such as Klebsiella and Haemophilus) but not enterococci or pseudomonas |
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What are two commonly used 3rd generation cephalosporins? |
1) ceftriaxone 2) ceftazidime |
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What is the spectrum of 3rd generation cephalosporins? |
Extended gram-negative cover (but not enterococci; only ceftazidime if active against pseudomonas) |
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How is ceftriaxone excreted? |
Hepatic (biliary) |
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What class of antibiotic is vancomycin? |
Glycopeptide |
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What is the spectrum of activity of vancomycin? |
Gram-positive bacteria only |
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What class of antibiotic does doxycycline belong to? |
Tetracyclines |
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What is the mechanism of action of tetracycline antibiotics? |
Bind irreversibly to 30S subunit of the bacterial ribosome and block binding of tRNA, thereby preventing protein synthesis |
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What are the three mechanisms of resistance to tetracycline antibiotics? |
1) impaired influx or enhanced efflux 2) production of proteins that interfere with tetracycline binding to ribosomes 3) enzymatic inactivation |
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What is the oral bioavailability of doxycycline? |
95-100℅ |
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What factors can inhibit absorption of doxycycline from the GI tract? |
Multivalent cations (such as calcium, magnesium, iron), dairy, antacids, alkaline pH |
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What drugs induce an increase in metabolism of doxycycline? |
Carbamazepine Phenytoin Barbiturates Alcohol |
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How is doxycycline excreted? |
Hepatic excretion |
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What is the major mechanism of adverse reaction to penicillins? |
Hypersensitivity |
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What are the common adverse reactions to tetracyclines? |
1) GI upset (nausea, vomiting, diarrhoea) 2) damage to growing bones and teeth |
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Name some commonly used macrolide antibiotics |
1) erythromycin 2) clarithromycin 3) azithromycin |
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What is the mechanism of action of macrolide antibiotics? |
Inhibition of protein synthesis by binding to the bacterial 50S ribosomal RNA |
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What are the three mechanisms of resistance to macrolide antibiotics? |
1) reduced permeability of cell membrane, or active efflux 2) production of esterases that hydrolyze macrolides 3) modification of ribosomal binding site |
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What are the advantages of clarithromycin over erythromycin? |
Less GI side effects and less frequent dosing |
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What is a potentially serious adverse effect of azithromycin? |
Prolonged QT interval |
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What is a common clinical use of clindamycin? |
Oral treatment of skin and soft tissue infections caused by methicillin-resistant staphylococci |
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What is the mechanism of action of chloramphenicol? |
Inhibition of microbial protein synthesis by reversible binding to the 50s subunit of the bacterial ribosome |
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What is the main clinical use of chloramphenicol? |
Topical treatment of eye infections (penetrates ocular tissues and aqueous humor) |
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What is a common adverse reaction to chloramphenicol? |
Dose-related reversible suppression of red cell production |
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What class of antimicrobial is linezolid, and what is its mechanism of action? |
Oxazolidinone Inhibits protein synthesis by binding to 23S ribosomal RNA and preventing formation of the ribosome complex |
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What is the bioavailability of linezolid? |
100℅ |
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What is the most common adverse effect of linezolid? |
Thrombocytopenia Can also cause anaemia and neutropenia, as well as serotonin syndrome when used in combination with serotonergic agents |
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What is the mechanism of action of aminoglycosides? |
Bind to 30S subunit and inhibit protein synthesis by: 1) interfering with initiation of peptide formation 2) causing misreading of mRNA 3) breaking up polysomes into nonfunctional monosomes |
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What factors influence the uptake of aminoglycosides? |
1) low extracellular pH and anaerobic conditions inhibit uptake 2) cell wall-active drugs such as penicillin or vancomycin increase uptake |
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What are the three mechanisms of resistance to aminoglycoside antibiotics? |
1) production of transferase enzymes that inactivate aminoglycosides 2) impaired uptake due to modification of uptake proteins, or due to maintenance of anaerobic conditions 3) alteration of the 30S ribosomal subunit receptor |
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What class of antimicrobial does gentamicin belong to? |
Aminoglycosides |
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How are aminoglycosides eliminated? |
Renally |
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What are the main adverse effects of aminoglycosides? |
1) ototoxicity 2) vestibulotoxicity 3) nephrotoxicity |
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What is the mechanism of action of trimethoprim? |
Inhibition of folate synthesis by inhibition of bacterial dihydrofolic acid reductase, which is necessary for purine (and hence DNA) synthesis |
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What is the mechanism of action of sulfonamides? |
Inhibition of folate synthesis by inhibition of dihydropteroate synthase |
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What is the mechanism of action of the fluoroquinolones? |
They block bacterial DNA synthesis by inhibiting bacterial topoisomerase II and IV |
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What is the oral bioavailability of the fluoroquinolones? |
80-95℅ |
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What mechanisms allow mycobacteria to be resistant to most antibiotics? |
1) slow growing / dormancy 2) lipid-rich cell wall is impermeable to many agents 3) reside within macrophages where they can be difficult to access 4) able to readily develop resistance |
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What four drugs are usually initiated in mycobacterial infection, prior to susceptibilities being determined? |
1) isoniazid 2) rifampin 3) pyrazinamide 4) ethambutol |
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What is the mechanism of action of isoniazid? |
Inhibits synthesis of mycolic acids, which are essential components of mycobacterial cell walls |
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What is the most common major toxic effect of isoniazid? |
Isoniazid-induced hepatitis |
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What can be administered to reverse peripheral neuropathy induced by isoniazid? |
Pyridoxine |
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What is the mechanism of action of rifampin? |
Inhibition of bacterial RNA synthesis by binding to beta-subunit of RNA polymerase |
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How is rifampin excreted? |
Hepatic (biliary) |
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Which azole has the best CNS penetration? |
Fluconazole |
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What is the mechanism of action of the azoles? |
Inhibition of fungal cytochrome P450 reduces ergosterol synthesis |
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What is the antimicrobial of choice for treatment of aspergillosis? |
Voriconazole |
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What is the antimicrobial of choice for the treatment of cryptococcal meningitis? |
Fluconazole |
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What is the mechanism of action of metronidazole? |
DNA damage caused by uptake of metronidazole that has been reduced by reaction with reduced ferrodoxin (occurs more within anaerobic cells) |
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What adverse effect can occur with high doses of penicillins in renal failure? |
Seizures |
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Emerging resistance of what organism discourages the use of a third generation cell cephalosporin? |
Enterobacter |
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Are aminoglycosides bactericidal or bacteriostatic? |
Bactericidal |
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Are beta-lactams bactericidal or bacteriostatic? |
Bactericidal |
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Is vancomycin bactericidal or bacteriostatic? |
Bactericidal |
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Is metronidazole bactericidal or bacteriostatic? |
Bactericidal |
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Are quinolones bactericidal or bacteriostatic? |
Bactericidal |
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Is chloramphenicol bactericidal or bacteriostatic? |
Bacteriostatic |
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Is clindamycin bactericidal or bacteriostatic? |
Bacteriostatic |
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Are macrolides bactericidal or bacteriostatic? |
Bacteriostatic |
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Are tetracyclines bactericidal or bacteriostatic? |
Bacteriostatic |
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In what circumstances is a bactericidal antibiotic required? |
1) endocarditis 2) meningitis 3) neutropenic patients |
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Do aminoglycosides exhibit time-dependent or concentration-dependent killing? |
Concentration-dependent killing |
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Do quinolones exhibit time-dependent or concentration-dependent killing? |
Concentration-dependent |
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Do beta-lactams exhibit time-dependent or concentration-dependent killing? |
Time-dependent |
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Does vancomycin exhibit time-dependent or concentration-dependent killing? |
Time-dependent |
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What antibiotics require routine serum concentration monitoring? |
1) vancomycin 2) aminoglycosides |
