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Antibiotics Flashcards

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1
Q

Beta-Lactam Mechanism of activity

A

kills bacteria by interfering with the synthesis of the bacterial cell wall

Binds to penicillin binding proteins (PBPs)

activity is limited to cells that are actively producing cell walls

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2
Q

Beta-Lactam mechanism of resistance

A

1) enzymatic destruction through beta lactamases (penicillinases in S. areus penicillin resistance)
2) alteration of penicillin-binding proteins (low-affinity PBP in MRSA called PBP2a)

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3
Q

Name the two major categories under Beta-Lactams.

A

Penicillins and Cephalosporins

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4
Q

Name the penicillin subclasses. What is the cellular target for all of these subclasses? What are the toxicities? Any exceptions?

A
  • Natural penicillins
  • Anti-staphylococccal penicillins
  • Aminopenicillins
  • Anti-speudomonal penicillins
  • Beta-lactam/Beta-lactam inhibitor combinations

Cellular target - Cell wall, inhibits cross-linking

Toxicities - rash, hypersensitivity, drug fever, antibiotic-associated diarrhea, C. difficile colitis, bone marrow suppression, seizures with high CNS levels, Coombs test, intersitital nephritis, anaphylaxis, allergic reactions

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5
Q

Natural penicillins

A
  • primarily for gram-positive bacteria
  • streptococcal infections (S. pyogenes, S. pneumoniae, enterococci)
  • will also cover N. meningitidis, Syphilis, and Listeria
  • will not cover most S. aureus because of penicillinase

ex. penicillin G (iv) and penicillin V (po)

Beta-Lactam, Penicillin

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6
Q

Anti-staphylococcal penicillins

A
  • not hydrolyzed by penicillinases or other beta-lactamases produced by S. aureus
  • used to treat MSSA
  • do not cover enterococci
  • note: workhorse for serious staphylococcal infections - endocarditis, osteomyelitis

ex. axacillin (iv), nofacillin (iv), dicloxacillin (po)

Beta-Lactam, Penicillin

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7
Q

Aminopenicillins

A
  • inactivated by many beta-lactamases
  • Gram-positive coverage similar to natural penicillins
  • covers some gram-negative infections
  • covers enterococci, L. monocytogenes, E. coli, Salmonella spp, and H. influenzae
  • increased activity due to ability to penetrate gram-negative outer membranes

ex.amoxicillin (po), ampicillin (iv and po)

Beta-Lactam, Penicillin

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8
Q

Anti-pseudomonal penicillins

A
  • Gram-positive coverage similar to natural penicillins, stronger gram-negative coverage
  • nosocomial gram-negative infections, including Pseudomonas
  • also covers many enterobacteriaceae

ex. piperacillin (iv), ticarcillin (iv)

Beta-Lactam, Penicillin

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9
Q

Beta-lactam/Beta-lactamase inhibitor combinations

A
  • gram-positive coverage
  • improved gram negative coverage and anaerobic activity due to the beta-lactamase inhibitor
  • covers S. aureus (MSSA)
  • covers gram-negatives including E. coli, K. pneumoniae, and Proteus mirabilis

ex. amoxicillin/clavulanate (po), ampicillin/sulbactam (iv), piperacillin/tazobactam (iv)

Beta-Lactam, Penicillin

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10
Q

Name the cephalosporin subclasses. What is the cellular target for all of these subclasses? What are the toxicities? Any exceptions?

A
  • 1st generation
  • 2nd generation
  • 3rd generation
  • 4th generation

Cellular target - cell wall, inhibits cell-wall cross-linking

Toxicities - rash, hypersensitivity (5-10% cross-reactivity with penicillins), antibiotic associated diarrhea, C. difficile colitis, neurotoxicity/seizures

  • cefepime notorious for neurotoxicity
  • ceftriazone assocciated with gallbladder sludge (caldium-ceftriazone salt percipitate)
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11
Q

1st generation

A
  • good activity against gram-positive organisms, including methicillin-susceptible S. aureus
  • most active cephalosporins against GPC, including MSSA (not enterococci)
  • covers gram-negatives such as E. coli, K. pneumoniae, and Proteus mirabilis

ex. cefazolin (iv), cephalexin (po)

note: cefazolin is common agent for surgical prophylaxis given skin coverage and some gram-negative

Beta-lactams, Cephalosporin

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12
Q

2nd generation

A
  • More gram-negative and less gram-positive activity
  • some in this group are active against anaerobes (cephamycins)

ex. cefuroxime (iv and po)

Beta-lactams, Cephalosporin

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13
Q

3rd generation

A
  • very active against most streptococci (except enterococci) and MSSA
  • good gram-negative coverage vs. Enterobacteriaceae but not Pseudomonas (except for ceftazidime)

ex. ceftriaxone (iv), cefixime (po), ceftazidime (iv)

note: ceftazidime is active against Pseudomonas and many nosocomial gram-negatives, but has no action against gram-positive or anaerobic activity

Beta-lactams, Cephalosporin

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14
Q

4th generation

A
  • maintains gram-positive coverage of all earlier generations
  • enhanced gram-negative and anti-pseudomonal coverage
  • remains active against many beta-lactamases produced by gram-negative organisms because of the zwitter-ion structure
  • very active against most streptococci (except enterococci) and MSSA

ex. cefepime (iv) and ceftaroline (iv)

note: ceftaroline is the only beta-lactam with activity against MRSA and some activity against Enterobacteriaceae

Beta-lactams, Cephalosporin

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15
Q

Monobactams

A
  • no gram-positive or anaerobic activity
  • active against Pseudomonas

ex. aztreonam

note: can be used in patients with allergy to penicillins/carbapenems

Toxicity: rash, hypersensitivity, antibiotic-associated diarrhea, C. difficile colitis, seizures with high CNS levels

Beta-lactam

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16
Q

Carbapenems

A
  • very broad gram-positive activity (including MSSA and enterococci)
  • anaerobic and gram-negative activity for Enterobacteriaceae, Pseudomonas, Acinetobacter

ex. imipenem (iv), meropenem (iv), doripenem (iv), ertapenem (iv)

note 1: ertapenem is not active against Pseudomonas

note 2: most reliable agents for Enterobacteriaceae with extended spectrum beta-lactamases

Toxicity: rash, hypersensitivity, antibiotic-associated diarrhea, C. difficile colitis, seizures with high CNS levels

Beta-lactams

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17
Q

Glycopeptides - Vancomycin mechanism of activity

A

inhibits bacterial cell wall synthesis, but at a different point than the beta-lactams

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18
Q

Glycopeptides - Vancomycin mechanisms of resistance

A

change in peptidoglycan with reduced binding to vancomycin - terminus altered to D-ala-D-lactate or D-ala-D-serine

production of thick cell wall with increased or false targets for vancomycin

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19
Q

Glycopeptides - Vancomycin spectrum of activity and toxicity

A
  • Gram-positive coverage only - aerobic and anaerobic
  • includes methicillin-resistant S. epidermidis, MRSA, and enterococci (not VRE)
  • intravenous vancomycin commonly used for serious infections of gram-positive organisms
  • oral vancomycin is not absorbed systmically, only used for infections within the intestinal lumen, primarily C. difficile
  • almost all gram-negatives are resistant

Toxicity: Red Man’s Syndrome/infusion reaction - not an allergy, nephrotoxicity, ototoxicity, bone marrow suppression

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20
Q

Lincosamides - Clindamycin mechanism of activity

A

inhibits proteins ynthesis by binding to the 50S subunit of the ribosome

blocks peptide bond formation, binding site is close to the site for erythromycin, shared resistance

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21
Q

Lincosamides - Clindamycin mechanism of resistance

A

methylation of the 50S subunit prevents clindamycin attachment

cross resistance with macrolides

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22
Q

Lincosamides - Clindamycin spectrum of activity and toxicity

A
  • good gram-positive and anaerobic activity
  • no gram-negative activity
  • active against most, but not all, MSSA and MRSA
  • good choice for empiric treatment of skin and soft tissue infections because of coverage for both streptocci and staphylococci
  • good oral bioavailability so may be used for outpatient therapy

toxicity: rash, antibiotic-associated diarrhea, C. difficile colits, esophagitis, hepatitis

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23
Q

Folate Antagonists - Trimethoprim-Sulfamethoxazole mechanism of action

A

blocks sequential steps in folate metabolism, synergistic combination

sulfonamides - compete with PABA for dihydropteroate synthas

trimethoprim - inhibits dihydrofolate reductase

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24
Q

Folate Antagonists - Trimethoprim-Sulfamethoxazole mechanisms of resistance

A

increased PABA concentration

enzymes with reduced affinity

loss of permeability

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25
Folate Antagonists - Trimethoprim-Sulfamethoxazole spectrum of activity and toxicity
* **Gram-positive** activity * S.aureus, including MRSA * **some streptococci**, but not reliable for causes of cellulitis * Listeria monocytogenes * _Some_ **Gram-negative** activity * **enterobacteriaceae** - acquired resistance in *E. coli* and others now limits use as first line for urinary tract infection **Toxicity**: rash, hypersensitivity, **_Stevens-Johnson Syndrome_**, and toxic epidermal necrolysis, aseptic meningitis, hepatitis, bone marrow suppression, hyperkalemia, elevated creatinine
26
Oxazolidinones - Linezolid mechanism of activity
inhibits protein synthesis by binding to 23S portion of 50S subunit prevents formation of ribosomal complex that initiates protein synthesis
27
Oxazolidinones - Linezolid mechanism of resistance
enterococci and staphylococci resistance due to point mutations in 23S rRNA requires mutations in two or more copies
28
Oxazolidinones - Linezolid spectrum of coverage and toxicity
* good **gram-positive** activity * active against **streptocci and staphylococci** * **MRSA and VRE** are susceptible * _no gram-negative_ activity * _no anaerobic_ activity * covers *Mycobacterium tuberculosis* and others **Toxicity**: **_bone marrow suppression_**, peripheral neuropathy, serotonin syndrome (do not take with SSRIs), thrombocytopenia
29
Lipopetide - Daptomycin mechanism of activity
binds to cell membrane causes depolarization due to K+ efflux depolarization disrupts cellular processes and leads to cell death no resistance mentioned
30
Lipopetide - Daptomycin spectrum of activity and toxicity
* _only_ **gram-positive** activity * active against **streptococci and staphylococci** * active against **MRSA and VRE** * cannot use in pulmonary infections due to being **inactivated by pulmonary surfactant** **Toxicity**: muscle toxicity (**_myopathy_**, rhabdomyolysis), eosinophilic pneumonia
31
Streptogrammins - quinupristin-dalfopristin
**mechanism** * binds to 50S ribosomal subunit and blocks peptide chain elongation **spectrum** * _bacteriostatic_ against *E. faecium* * _bactericidal_ against *S. aureus* (including MRSA) * **not active** against *E. faecalis* **toxicity** * phlebitis, arthralgias, myalgias, GI upset, elevated bilirubin **note**: may have a role in treatment failure of first line agents vs. MRSA or VRE, not commonly used
32
Rifamycin - Rifampin
**mechanism** * inhibits DNA-dependent RNA-polymerase, preventing chain initiation **spectrum** * S. aureus, including MRSA * used in combination for *Mycobacterium tuberculosis* **toxicity** * hepatitis, reddish discoloration of body fluids, rash, numerous drug-drug interactions **note**: penetration into biofilms makes this useful for prosthetic material infections due to *S. aureus*
33
Tetracyclines
**mechanism** * binds to 30S ribosomal subunit and blocks binding of aminoacyl RNA **spectrum** * S. aureus, including MRSA * Chlamydia, Mycoplasma, Lyme disease, Tularemia, Brucella, Rickettsiae **toxicity** * GI upset, diarrhea, photosensitivity, vestibular symptoms, increased skin pigmentation, tooth discoloration in children * ex. doxycycline (iv and po) and minocycline (po)*
34
factors that influence whether the antibiotic is right
speed IV vs. oral breadth of empiric therapy antibiotic resistance of pathogen MIC of the effective antibiotic for the pathogen(s)
35
steps take for patients in septic shock or severe sepsis
1) aggressive fluid resuscitation wtihin the first six hours 2) cultures and imaging studies, at least 2 sets of blood cultures 3) within the first hour after sepsis is identified, adminsiter broad, effective antimicrobials that has Gram positive and Gram negative coverage
36
SIRS criteria
Systemic Inflammatory Response Sydrome 2 or more of the following: * Temp \>38 or \< 36 * heart rate \> 90 * respiratory rate \> 20 or PaCO2 \< 32mmHg * WBC \> 12,000/mm3 or \<4000/mm3
37
sepsis
SIRS + source of infection present or suspected
38
severe sepsis
sepsis with organ dysfunction, hypoperfusion, hypotension, and/or lactic acidosis
39
septic shock
severe sepsis with hypotension despite adequate fluid resuscitation
40
sequestered vs. non-sequestered site of infection
**non-sequestered** - site that has no anatomic or physiologic barriers to the antibiotic such as well perfused skin, kineys, lungs **sequestered** - prostate, brain, bone, large abscess, poorly perfused site (severe trauma)
41
broad spectrum antibiotic combination for penicillin-allergic patients
vancomycin + aztreonam + metronidazole
42
Fluoroquinolones mechanism of action
inhibits DNA gyrase in Gram-negative organisms inhibits Topoisomerase IV in Gram-positive organisms
43
Fluoroquinolones mechanism of resistance
1) a single point mutation in the bacterial chromosome can result in resistance by altering affinity of the antibiotic to bind to the target enzyme, most common mechanism of resistance 2) plasmids can code for efflux pumps
44
Fluoroquinolones spectrum of activity and toxicity
* all have **Gram-negative** activity * activity against **intracellular organisms** such as *Chlamydophila pneumoniae*, *Legionella* spp., and *Mycoplasma pneumoniae* * *S. pneumoniae* activity * MSSA, though resistance may develop on therapy * good activity against Enterobacteriaceae and *Pseudomonas* **Toxicity** * tendonitis/**_tendon rupture_**, antibiotic-associated diarrhea, *C. difficile* colitis, CNS toxicity, QTc prolongation **note 1**: ciprofloxacin is very useful against genitourinary infections, bu tresistance is common due to overuse **note 2**: respiratory fluoroquinolones can be used as a single agent for community acquired pneumonia (active against typical and atypical organisms) *ex. ciprofloxacin (iv and po), levofloxacin (iv and po), and moxifloxacin (iv and po)*
45
Aminoglycosides mechanism of action
binds irreversibly to the 30S ribosome within the cytoplasm and inhibit protein synthesis by preventing the translocation of peptidyl-t-RNA bacterial cell death depends on high concentrations of the drug reaching the site of infection, and oxygen is necessary **postantibiotic effect** - after the serum concentration ahs fallen, residual intracellular drug remains bacteriocidal
46
Aminoglycosides mechanism of resistance
1) drug inactivation, plasmid that encodes for an enzyme that alters the drug 2) rare mutations that alter the structure of the ribosomes so that binding is impaired natureal resistance: 1) bacteria is an anaerobe and growing in an anaerobic enviroment, drug can't cross the cytoplasmic membrane 2) ribosome has low affinity for the drug
47
Aminoglycosides spectrum of activity and toxicity
* targets **aerobic Gram-negatives** * active against *Pseudomonas* * used as a _second agent_ for serious **staphylococcal or enterococcal** infections * works against *S. aureus* **Toxicity**: **_nephrotoxicity_**, ototoxicity, neuromuscular blockade *ex. gentamicin (iv), tobramycin (iv), amikacin (iv) - **know these!***
48
Nitroimidazoles - Metronidazole mechanism of action and toxicity
intracellularly generates short-live reactive intermediates that damage DNA by electron transfer system
49
Nitroimidazoles - Metronidazole spectrum of activity
* active against **anaerobic bacteria** * *Bacterioides*, *C. difficile*, *Trichomonas*, *Giardia*, *E. histolytica* **Toxicity**: headaches, nausea, metallic taste, **disulfuram-like reaction**, neuropathy with prolonged use
50
Macrolides mechanism of action
binds to the 50S ribosomal subunit and blocks peptide bond formation
51
Macrolides spectrum of coverage and toxicity
* **Gram positive** - *S. pneumoniae* * **Gram-negative** - *H. influenzae*, *Neisseria* spp., *B. pertussis*, *Campylobacter* * **Atypical** - *Mycoplasma*, *Legionella*, *Chlamydia* **Toxicity**: GI upset, diarrhea, QTc prolongation leading to rosades des pointes, ventricular tachycardia and sudden death *ex. erythromycin (po), azithromycin (iv and po), clarithromycin (po)*
52
Type I Antibiotic Allergy
Immediate **Mechanism** * IgE mediated * binds to mast cells and basophils * histamine, leukotrienes, and prostaglandins released **Symptoms** * urticaria, angioedema, anaphylaxis * onset is rapid **Management** * epinephrine, antihistamines, H2-blocekrs, glucocorticoids
53
Type II Antibiotic Allergy
Cytotoxic **Mechanism** * Antibody mediated (usually IgG) * leads to tissue destruction **Symptoms** * immune hemolytic anemia * thrombocytopenia
54
Type III Antibiotic Allergy
Immune complex **Mechanism** * Immune complex disease * soluble immune complex (IgG boudn to drug) * deposition and complement activation **Symptoms** * serum sickness * drug fever * vasculitis
55
Type IV Antibiotic Allergy
Delayed **Mechanism** * T cell mediated * sensitized lymphocytes **Symptoms** * Maculopaopular exanthem (outward from central location) * contact dermatitis * fixed drug eruption * Stevens-Johnson Syndrome * Toxic Epidermal Necrolysis
56
SJS and TEN
Stevens Johnson Syndrome and Toxic Epidermal Necrolysis severe idiosyncratic reactions characterized by fever, mucocutaneous lesions, and sloughing of the epidermis both are generally triggered by medications, antibiotics being the most likely
57
Streptogrammins - quinupristin-dalfopristin (iv) mechanism of action
binds to 50S ribosomal subunit, blocks peptide chain elongation
58
Streptogrammins - quinupristin-dalfopristin (iv) spectrum of activity and toxicity
* _bacteriostatic_ against *E. faecium* (including VRE) * _bactericidal_ vs. *S. aureus* (including MRSA) * **not active** against *E. faecalis* **Toxicity**: phlebitis, arthralgias, myalgias, GI upset, elevated bilirubin **note**: may have role in treatment failure of first line agents vs. MRSA or VRE, not commonly used
59
Chloramphenicol - chloramphenicol (iv and po) mechanism of action
binds to 50S ribosomal subunit and blocks aminoacyl tRNA attachment
60
Chloramphenicol - chloramphenicol (iv and po) spectrum of activity and toxcitiy
* **Streptococci** * *H. influenzae*, *Neisseria* spp. * *Salmonella typi*, *Brucella* spp., *Bordetella pertusis* * **most anaerobes** * *Rickettsiae* **Toxicity**: * reversible bone marrow toxicity, aplastic anemia, Gray baby syndrome **note**: very infrequently used int he US
61
Glycyclcyline - tigecycline (iv) mechanism, spectrum of action, and toxicity
**_Tetracycline subclass_** **mechanism** * binds to 30S ribosomal subunit, blocks binding of aminoacyl tRNA **Spectrum** * MSSA, MRSA, VRE * active against many **gram-negatives**, including some MDR *Acinebacter* and carbapenem-resistant Enterobacteriaceae (CRE) **not active** against *Pseudomonas* **Toxicity**: nausea and vomiting, photosensitivity, pancreatitis **note**: bacteriostatic and does not achieve high serum levels, so despite its very broad activity, it is less useful for serious infections
62
Urinary antiseptics - nitrofurantoin (po) mechanism of action
inhibits bacterial acetyl-coenzyme A, interfering with the organism's carbohydrate metabolism
63
Urinary antiseptics - nitrofurantoin (po) spectrum of activity and toxicity
* **Enterococci**, including VRE * *S. sapprophyticus* * **gram negatives**, including *E. coli* **Toxicity**: interstitial pneumonia wiht fibrosis, hepatitis, rash, polyneuropathy **note**: useful first line agent for UTI, except in elderly or others with reduced CrCl
64
Polymixins mechanism of action
disrupts the cell membrane permeability by charge alteration
65
Polymixins spectrum of activity and toxicity
* **Gram-negative** activity, including **Enterobacteriaceae** and *Pseudomonas* **Toxicity**: nephrotoxicity, neuromuscular blockade **note**: used in combination against very resistant organisms - MDR *Pseudomonas*, MDR *Acinetobacter*, carbapenem-resistant Enterobacteriaceae (CRE) *ex. colistin (iv) and polymixin B (iv)*
66
antibiotics with time-dependent activity
Beta-lactams Carbapenems Vancomycin Clindamycin Linezolid
67
antibiotics with concentration-dependent activity
aminoglycosides fluoroquinolones metronidazole

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