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Block 2 - Bugs and Drugs > Antibacterials > Flashcards

Antibacterials Flashcards

(86 cards)

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0
Q

Sulfonamides - mechanism of resistance

A

Clinical isolates have higher concentrations of pABA

Altered DAS that doesn’t bind sulfonamides as well

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1
Q

Sulfonamides - mechanism of action

A

Bacteriostatic only
Resistance is common
Analogs of pABA = comp. inhibitors of dihydropteroic acid synthase (humans don’t have) - bacteria cannot synthesize folate for NT synthesis
Bacterial DHFR inhibited by trimethoprim

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2
Q

Sulfonamides - pharmacokinetics

A

Well absorbed orally
Distribution everywhere including CNS
Antagonized by tissue breakdown products
Sig. Amount acetylated and inactivated in liver
Glomerular filtration elimination

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3
Q

Sulfonamide - adverse effects

A

Allergies
GI nausea and stomach distress
Hemolytic anemia - don’t give to patients with G6PD deficiency - cant neutralize ROS generated by sulfa drugs
Crystalluria - drink water!

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4
Q

Sulfonamides - therapeutic uses

A

Alone - nocardia (often with trimethoprim), minor UTIs (also)
Sulfonamide plus DHFR inhibitor - synergistic, co-trimoxazole active against many gram- and gram+, some fungi, some MRSA, inactive against anaerobes

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5
Q

Sulfisoxazole

A

Most popular for single drug therapy
Free and acetylated forms soluble
Few adverse reactions
Good CSF concentration

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6
Q

Sulfamethoxazole

A

Pharmacokinetics matched to trimethoprim

Longer half life than sulfisoxazole

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7
Q

Co-trimoxazole

A 
Combo can be bacteriocidal 
Both absorbed into CSF 
Active against gram+ and gram- 
Major use is UTIs 
Broad spectrum used in variety of infections
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8
Q

Fluoroquinolones - mechanism of action

A

Synthetic drugs
Bacteriostatic or bacteriocidal depending on dose
Binds to topoisomerase-DNA complex inhibiting replication and transcription
Main target in gram+ = topoisomerase IV
main target in gram- = gyrase

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9
Q

Fluoroquinolones - pharmacokinetics

A

Orally or IV - well absorbed from GI
Absorption inhibited in presence of cations (no milk, antacids)
Good penetration except not into CSF
Most eliminated by kidney, some by liver

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10
Q

Fluoroquinolones - adverse effects

A

Severe side effects rare
GI disturbances
CNS effects - dizziness, headaches, insomnia
Cartilage weakening in children - don’t give pregnant women either
Inhibit theophylline metabolism - can cause seizures
Phototoxicity from uv or sun

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11
Q

Fluoroquinolones - resistance

A

Altered topoisomerase target
New mechanisms emerging
Recommend use only for life threatening infections or failure of first agents

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12
Q

Fluroquinolones - therapeutic uses

A

Used in many infections
Only aerobes affected
Can sometimes replace amino glycosides for serious gram-

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13
Q

Ciprofloxacin

A

Fluoroquinolone
Not for resp - poor activity against strep
Gram- and some gram+

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14
Q

Levofloxacin

A

Fluoroquinolone
Active against strep –> resp inf
Also against staph, and many gram+ and gram-

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15
Q

Nitrofurantoin

A

Used for chronic suppression of bacterial UTIs
Bacteriostatic and bacteriocidal
Reduced, then oxidized - generates toxic intermediates that damage DNA and macromolecules
Best at pH 5.5
Can cause hemolytic anemia in newborns - don’t give to pregnant women near term

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16
Q

Rifamycins - mechanism of action

A

Bind to DNA directed RNA polymerase and allosterically inhibit it - transcription blocked
Bacteriocidal
Selectivity for prokaryotic polymerase
Resistance often develops - rarely used alone

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17
Q

Rifampin

A 
Major use against Tb
Prophylaxis of close contact to meningococcal meningitis 
Activity against legionella 
Synergistically with other drugs
Concentrates in saliva
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18
Q

Rifabutin

A

Useful for both Tb and mycobacterium avium (but not mainline)

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19
Q

Beta lactams - mechanism of action

A

Bacteriocidal
Mainly penicillin and cephalosporin
Interfere with cell wall production remodeling
Activate autolysins - cause cell to lyse after beta lactam acts
Final step in cell wall assembly is catalyzed by transpeptidase (aka penicillin binding proteins = PBPs) - binds to d-ala-d-ala
Beta lactams resemble d-ala-d-ala and irreversibly bind to enzyme

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20
Q

Beta lactams - resistance

A

Outer membrane of gram- restrict access to periplasm which is site of action
Acquired beta lactamase activity - hydrolyze amine linkage
Alteration of PBPs
Alteration of porins in outer membrane of gram-

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21
Q

Beta lactams - pharmacokinetics

A

Most acid labile - not administered orally
IV injection preferred for life threatening infection
Short half lives
Distribution good except limited in CSF and eye
Renal elimination - glomerular filtration and secretion pump (blocked by probenecid)

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22
Q

Beta lactams - adverse reactions

A

Allergy - major frequency determinants are penicillin molecules linked to lysine residues of serum proteins, minor frequency determinants are penicillin itself and breakdown products - can be life threatening
If MUST use - desensitization but its dangerous
Large amounts of sodium can cause problems
Pen can accumulate in brain due to probenecid - seizures
Cephalosporin may cause super infections

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23
Q

Beta lactams - therapeutic uses

A

Most sensitive are gram+ and spirochetes
Broader spectrums have some use against gram- but less against gram+
*mainline bacteriocidal drugs for gram+ infections

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24
Penicillin g
Narrow spectrum penicillin Half life 30-60 min Acid labile --> I.m. Injection Pen g benzathine - half life 1-2 weeks Effective for gram+ cocci (except entero) and bacilli if not resistant, neisseria, spirochetes Staph a. And most neisseria gonorrhea now resistant
25
Nafcillin
Anti staph penicillin | Acid labile --> given IV
26
Oxacillin
Anti staph penicillin | Acid stable --> oral for less severe infections, also IV
27
Ampicillin and amoxicillin
Broad spectrum penicillins Acid stable --> oral F higher for amoxicillin, admin less often Useful against some gram- bacilli Activity against gram+ adequate but not as good as pen g
28
Ticarcillin
Anti pseudomonal penicillin Parenteral admin Less active against gram+ than pen g More potent than original
29
Piperacillin
``` Broadest spectrum penicillin Most active drug in this class Useful for wide variety of serious gram- inf ```
30
Cephalosporins - general attributes
Good subs for pen in allergics Less sensitive to beta lactamases than pen (but still to staph a.) Penetration into CSF Prophylaxis during surgery
31
First generation cephalosporins
Good gram+ coverage Useful but limited gram- coverage Good for penicillinase producing staph strains
32
Cefazolin
Parenteral first generation cephalosporin
33
Cephalexin
Oral first generation cephalosporin
34
Second generation cephalosporins
Increased coverage of gram- bacilli | Some have good activity against anaerobes
35
Cefuroxime and cefoxitin
Parenteral second generation cephalosporins | Cefoxitin - good anaerobic agent but resistance in b. fragilis
36
Third generation cephalosporins
Useful for gram- Good CSF penetration Super infections are a problem
37
Cefotaxime
Third generation cephalosporins Resistant to beta lactamases Good against gram+ and gram- Great for meningitis
38
Ceftriaxone
Third generation cephalosporins Longest half life of class Drug of first choice for gonorrhea
39
Ceftazidime
Third generation cephalosporins | Antipseudomonal
40
Cefepime
Fourth and fifth generation cephalosporins Stronger activity against staph More resistant to beta lactamases
41
Imipenem
Part of carbopenem class of beta lactams Broad spectrum - active against gram+, gram-, aerobes, anaerobes Resistant to beta lactamases Inactivated in renal tubules by dihydropeptidases - give with cilastatin which inhibits this Given in combo with amino glycosides for serious gram- inf
42
Beta lactamase inhibitors
Clavulanic acid | Used in combo with other beta lactams
43
Vancomycin - mechanism of action
Inhibit cell wall synthesis Bacteriocidal Limited for gram+ - cant penetrate outer membrane Binds to d-ala-d-ala shielding from transpeptidase Drug of last resort for MRSA, drug resistant eneterococci, others Resistance - bacteria sub d-ala-d-lactate
44
Vancomycin - pharmacokinetics
Poorly absorbed from GI Parenteral admin Good penetration but not across BBB unless meninges inflamed Glomerular filtration
45
Vancomycin - adverse effects
Rapid admin can cause histamine release --> flushing, rashes, hypotension Can be ototoxic Possible nephrotoxicity Do NOT combine with aminoglycosides
46
Vancomycin - therapeutic indications
Useful for serious gram+ First choice for MRSA Useful against enterococcus, endocarditis from strep viridans, and c. Dificile
47
Aminoglycosides - mechanism of action
Often given in combo with pen or cephalosporin esp for entero. Endocarditis Bacteriocidal - mostly against gram- Diffuse through porins but must be pumped across plasma membrane - dependent on neutral or high external ph, oxy, normal osmolarity - not effective in anaerobic environment Low concentrations cause mRNA misreading by binding to 30s on ribosome - altered proteins get into membrane and destabilize it leading to influx and lysis
48
Aminoglycosides - mechanism of resistance
Transferase enzyme add moieties to carb groups and render drug unable to bind ribosomes
49
Aminoglycosides - pharmacokinetics
Polar and charged - poor absorption from GI tract Given IV or I.M or s.q Distribution limited to extra cellular fluids Elim by glomerular filtration
50
Aminoglycosides - adverse effects
Therapeutic index is low Potential for ototoxic and nephrotoxicity Bacteria have post antibiotic effect Neuromuscular blockade in susceptible patients (myasthenia) Damage to optic nerve
51
Streptomycin
Now resistance | Useful combo with beta lactam for endocarditis from entero, viridans, drug resistant tb, tularemia, and plague
52
Gentamicin and tobramycin
Mainline aminoglycosides Imp for gram- inf Admin intrathecally or intraventricularly for CNS inf
53
Amikacin
Aminglycoside More potent against gram- More resistant to transferase enzymes
54
Neomycin
Aminoglycosides Treatment or prophylaxis of topical inf Too toxic for parenteral use Frequently to prepare bowel for surgery
55
Tetracyclines - mechanism of action
Bacteriostatic | Target is 30s ribosomal subunit - inhibits tRNA binding
56
Tetracycline - resistance
Enter cell through transporter | Some cannot accumulate drug in cytoplasm - acquire gene to pump it right back out
57
Tetracyclines - pharmacokinetics Also doxycycline And minocyclin
Oral admin T - incomplete oral aborption, short half life, glom filtration D and m - almost completely absorbed, longer acting, more lipophilic, hepatic elim (But mino also a little by kidney) Absorption limited in presence of cations Lipophilic accumulates in fat, all stored in bone (Vd > body water) Penetration into all tissue good including fetus
58
Tetracyclines - adverse effects
Broad spectrum - superinfections Discolor teeth in children - don't give during pregnancy either Inhibit bone growth and cause stunting in children Hepetatoxicity - esp during pregnancy Photooxidize from uv Acute GI distress
59
Tetracyclines - therapeutic uses
Broad spectrum - lots of resistance but still niche uses First choice for rickettsia Can be used for MRSA Freq use for mycoplasma pneumonia and chlamydia Gonorrhea and syphilis in pen allergic patients
60
Macrolides - mechanism of action and resistance
Bind to 50s ribosomal subunit - inhibit peptidyl transferase Bacteriostatic for the most part For gram+ Subs for beta lactams in allergic patients Resistance by either decrease in influx, elaboration of inactivating enzymes, change in ribosomal subunit
61
Macrolides - pharmacokinetics
Usually oral admin Erythromycin - acid labile but has preparation that protects it Clarithromycin and azithromycin more acid stable Wide distribution but not to CSF Elim in bile
62
Macrolides - adverse effects
Serious are rare Epigastric distress Many drug drug interactions
63
Macrolides - therapeutic uses
Gram+ inf esp strep and listeria Chlamydia after tetracyclines First choice for legionella Gonorrhea and syphillis in pen allergic pregnant women
64
Erythromycin
Macrolide Can concentrate several fold in bacterial cells Stronger against gram+
65
Clarithromycin
Macrolide Better f than erythro Activity against mycobacterium avium
66
Azithromycin
Macrolide Can concentrate in many tissues as well as macrophages and is released over several days 5 day treatment usually sufficient
67
Clindamycin
Major use against anaerobes or prophylaxis of endocarditis 50s ribosomal binder - antagonized by macrolides Oral or IV - doesn't cross BBB Superinfections and skin rashes common
68
Quinupristin-dalfopristin
D binds first and stimulates binding of the other - synergy Binds 50s ribosome subunit Bacteriocidal Bacteria have post antibiotic effect IV admin Metabolized in liver and excreted in bile Inhibits p450 - watch for drug interactions Reserved for treatment of multidrug resistant infections
69
Linezolid
Good for resistant gram+ inf Bind to unique site of 50s ribosome subunit Bacteriostatic except cidal for strep Oral or IV - good f Tongue discoloration, superficial fungus inf, headache, bone marrow suppression if more than 14 days
70
Daptomycin
Good for resistance gram+ inf Preferentially binds to phosphatidyl glycerol in bacterial membranes (absent in mammals) and causes depolarization No interactions Binds to surfactant - don't use for pulmonary inf Many serious side effects - reserved for life threatening inf
71
Metronidazole
Kills anaerobic bacteria and Protozoa Reduced drug generate intermediates toxic to macromolecules Patients should not drink alcohol
72
Bacitracin
Topical use for gram+ and gram- inf | Orally for c. Dificile in GI tract
73
What are the drugs for leprosy?
Dapsone - sulfonamide like action | Usually in combo with rifampin
74
What are the two techniques of susceptibility testing?
Broth dilution - inoculate tube of broth with particular bacterium and test effects of different antimicrobials - mean inhibitory concentration is one that inhibits growth of bacteria Disk diffusion - place anti microbial impregnated disk on top of agar plate inoculated with lawn of bacterium
75
What is the mean bactericidal concentration?
One required to kill 99.9% of bacteria in solution over 24 hr period Must plate on agar to measure
76
What is an e test?
Variant of disk diffusion test Strip with gradient of increasing concentrations of anti microbial placed onto lawn of bacteria MIC is where zone of inhibition starts
77
What is the technical difference between bacteriocidal and Bacteriostatic drugs?
Bacteriocidal kills more than 99.9% in 24 hrs = 3 log kill | Bacteriostatic only kills 99% = 2 logs
78
What is the 90-60 rule?
Infections due to susceptible isolates will respond only 90% of time to therapy Infections due to resistant isolates or wrong anti microbial will respond 60% of the time Host factors more important in determining outcome than simply knowing MIC
79
How do abscesses interact with antibiotics?
Low ph inside cavities inactivate many antibiotics, especially aminoglycosides
80
What are three special situations difficult to treat?
Endocarditis Febrile neutropenia Prosthetic devices
81
What is the difference between time dependent and concentration dependent killing?
Time dependent - longer above MIC is more effective | Concentration - higher concentration above MIC more and more effective (Cmax/MIC), show post antibiotic effect
82
Which antibiotics show time dependent killing?
``` Penicillins and cephalosporins Max killing occurs when drug concentration/MIC is 2-4 Tetracyclines Azole antifungals Linezolid and ketolides Streptogramins ```
83
Which antibiotics show concentration dependent killing?
``` Aminoglycosides Peak level 10 fold greater than MIC desired Fluoroquinolones Amphotericin b Echinocandins Flucytosine Nystatin Daptomycin ```
84
Which drugs have both types of killing?
Macrolides Primary parameter is AUC/MIC active intracellularly and extracellularly
85
Which antibiotics cannot penetrate into cells?
Beta lactams Aminoglycosides Vancomycin Daptomycin

Block 2 - Bugs and Drugs (9 decks)

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