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Antibacterials Pt. 2 Flashcards

1
Q 
General Mechanisms of Action
Aminoglycosides:
Tetracycline and Chloramphenicol:
Chloramphenicol:
Erythromycin and Clindamycin:
A

Aminoglycosides: Premature release of ribosome from mRNA - misreading of mRNA
Tetracycline and Chloramphenicol: Prevent tRNA from binding
Chloramphenicol: Blocks peptide bond formation
Erythromycin and Clindamycin: Block translocation step

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2
Q

Aminoglycosides

A

Gentamicin
Tobramycin
Amikacin

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3
Q

Tetracyclines

A

Doxycycline
Minocycline
Tigecycline (Glycycline)

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4
Q

Macrolides

A

Erythromycin
Clarithromycin
Azithromycin

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5
Q

Oxazilidinones

A

Linezolid

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6
Q

Aminoglycosides - General Properties
Bactericidal or Static?
Administration:
Mechanism:

A

Bactericidal
Administration: IV, IM, topical
Mechanism: Transported into bacteria by energy requiring aerobic process
- Binds to several ribosomal sites (30S/50S interface)
- Stops initiation and causes premature release of ribosome
- Causes mRNA misreading

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7
Q

Uses of Aminoglycosides

A

Primarily for gram-neg. ‘aerobic’ bacilli (Often in combination with cell wall inhibitors or quinolones) - synergism
Poor activity against anaerobes
Gram positive activity requires drug combinations
- Cell wall inhibitors enhance permeability of aminoglycosides
Use restricted to serious infections (due to side effects)

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8
Q

Why don’t you mix aminoglycosides with β-lactams in vitro?

A

Chemical reaction inactivates the aminoglycosides

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9
Q

Post antibiotic effect of aminoglycosides

A

Sustained activity for several hours after aminoglycoside concentration has dropped below effective levels
- Concentration dependent killing
Less frequent dosing
Problem: Toxicity is dose-related

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10
Q

When do you use amikacin?

A

Choice agent for gentamicin and tobramycin -resistant strains

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11
Q

Aminoglycosides side effects

A

Narrow therapeutic window
Nephrotoxicity (usually reversible)
Ototoxicity (mostly irreversible)
Nueromuscular blockade

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12
Q

Tetracyclines: Mechanism

A

Bacteriostatic
Transported into the cells by protein carrier system
Prevent attachment of aminoacyl-tRNA bind to 30S ribosomal subunits

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13
Q

Tetracycline Resistance

A

Drug efflux pump

- Resistance to one tetracycline often implies resistance to them all

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14
Q

Uses of Tetracyclines (no longer broad spectrum)

A

Preferred agents for “unusual” bugs

  • Rickettsia
  • Lyme Disease
  • Chlamydia, Mycoplasma, Ureaplasma
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15
Q

Doxycycline
Uses:
Half Life:

A

Uses: For patients with impaired renal function; alternative for PenG-sensitive syphilis and uncomplicated N. gonorrhoeae
Half Life: 24 hours

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16
Q

Minocycline
Uses:
Half Life:

A

Uses: Alternative for PenG-sensitive syphilis and uncomplicated gonorrhea
Half Life: 11-26 hours

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17
Q

Tetracyclines Administration:

What slows absorption?

A

Oral, Parenteral
Binds calcium which inhibits absorption
- Tetracycline > minocycline > doxycycline
- Do not take with high-calcium foods

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18
Q

Side effects of Tetracyclines

A 
Gastrointestinal disturbances including enterocolitis
Candida superinfection in coon
Photosensitization with rash
Teeth discoloration
- Avoid use in children <8 years old
- Contraindicated in pregnancy
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19
Q

Tigecycline (New drug class - Glycylcyclines)
Mechanism:
Resistance:

A

Mechanism: Bacteriostatic; like tetracyclines but also binds additional sites in the ribosomes
Resistance: No cross resistance with other antibacterials including tetracyclines

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20
Q

Tigecycline Uses:
Gram negatives:
Gram Positives:
Anaerobes:

A
  • Skin/Skin structure infections
  • Complicated intra-abdominal infections
  • CAP (community-acquired pneumonia)

Gram negatives: E. Coli, Citrobacter, Klebsiella, Enterobacter (NOT pseudomonas)
Gram Positives: Staphylococcus (MSSA and MRSA), Streptococcus
Anaerobes: Bacteroides, Clostridium Perfringens

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21
Q

Tigecycline
Administration:
Adverse reactions:

A

Administration: IV only (does not inhibit P450s)
Adverse reactions: Nausea, vomiting (35%), enterocolitis
- Other side effects similar to tetracylines including calcium binding
- FDA alert: increased risk of DEATH

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22
Q

Chloramphenicol
Mechanism:
Resistance:

A

Mechanism: Interferes with binding of aminoacyl-tRNA to 50S ribosomal subunit and inhibits peptide bond formation
Resistance: Acetylation by CAT (chloramphenicol transacetylase)

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23
Q

Chloramphenicol

Spectrum of activity:

A

Broad

  • Aerobes and anaerobes
  • Gram-pos. and gram-neg.
  • Including Bacteroides fragilis
24
Q

Chloramphenicol - Current Indications

A

Meningitis - alternative for those with serious cephalosporin allergy (N. Meningitidis, S. Pneumoniae)
Brain abscesses (often anaerobes)
H. Influenzae
Salmonella Typhi/Invasive salmonella infections
* Generally bacteriostatic

25
Chloramphenicol - Side Effects
Bone Marrow Depression - Fatal aplastic anemia (1 in 30,000) Grey baby syndrome Optic Neuritis and Blindness GI effects including enterocolitis
26
Macrolides Drugs: Mechanism:
Drugs: Erythromycin; Clarithromycin; Azithromycin Mechanism: Bacteriostatic - binds to 50S subunit, blocks translocation along ribosomes
27
Erythromycin - Uses
Primarily against gram positive - Streptococcus - Recommended for Strep. throat in penicillin-allergic patients - Some Staph Also effective against "unusual" or "atypical" bugs: - Chlamydia, Mycoplasma - Legionella (azithromycin now preferred) - Bordetella
28
Erythromycin - Side Effects
Nausea, vomiting (20-40%) - from enhance GI motility Inhibits CYP3A4 metabolism/excretion of many drugs Increases risk of arrythmias and cardiac arrest (doubles the risk on its own)
29
Clarithromycin Mechanism: Differences from Erythromycin:
``` Mechanism: Similar to erythromycin Differences from Erythromycin: - Better kinetics: less frequent dosing - Less GI motility effects (50% less) - Somewhat wider antibacterial spectrum * Also some CV risk ```
30
Clarithromycin Uses: | 3 drug combo:
``` Same as erythromycin plus: - Haemophilus influenzae, Moraxella - Penicillin-resistant Strep. pneumoniae - Atypical mycobacteria - Lycensed for Helicobacter pylori 3 drug combo: 2 antibacterials: clarithromycin + amoxicillin + acid blocker ```
31
FDA-approved treatments for Helicobacter eradication
1) Clarithromycin + amoxicillin + omeprazole 2) Metronidazole + tetracyline + bismuth subsalicylate + PPI * combinations are more effective than single antibiotic
32
Azithromycin - Uses
- Very common for outpatient respiratory tract infections - Genital infections (chlamydia) - Gonorrhea (CDC recommends ceftriaxone + azithromycin or doxycycline)
33
Macrolides Adverse Reactions:
Erythromycin > Clarithromycin > Azithromycin Azithromycin has few effects on CYP3A4 - QT prolongation
34
Clindamycin | Mechanism:
Binds to 50S ribosomal subunit, locks translocation along ribosomes - Significant cause of enterocolitis
35
Clindamycin Uses
Gram Pos. cocci (Strep and MSSA) - NOT for enterococcus or hospital acquired MRSA - Suppresses bacterial toxin production (Strep. and Staph.) Many anaerobes including Bacteroides fragilis - NOT FOR C. DIFFICILE!!
36
Clindamycin side effects
GI irritation, Diarrhea (about 20%) Antibiotic-associated enterocolitis (3-5%) Hepatotoxicity
37
Linezolid | Mechanism:
Bacteriostatic - Inhibits protein synthesis - Binds to 50S ribosomal subunit, interfering with formation of 70S initiation complex
38
Linezolid Uses Skin infections: Nosocomial pneumonia:
``` Gram positive spectrum Skin infections - VRE: vancomycin resistant Enterococcus faecium - Staph Aureus - Streptococcus, group. A and B Nosocomial pneumonia - Strep. Pneumoniae - Staphylococcus ```
39
Linezolid Side effects
``` Non selective inhibitor of MAO - Avoid foods with tyramin - Possible drug interactions Diarrhea, superinfection including enterocolitis Headache, nausea/vomiting Bone marrow suppression ```
40
Anti-folates | Drugs:
Sulfonamides: Sulfamethoxazole, Sulfadiazine | Trimethoprim
41
Sulfonamides | Mechanism of Action:
Bacteriostatic | Competitive analogs of p-aminobenzoic acid, a precursor in folate synthesis
42
Sulfonamide - Uses
Today, most commonly used sulfonamides are combined with other antibacterials
43
Which sulfonamide is used with trimethoprim and why?
Sulfamethoxazole (synergistic combination) | Best pharmacokinetic match to trimethoprim (proper ratio)
44
Silver sulfadiazine use
Used topically for infection in burn patients
45
Sulfonamides - Side Effects
``` Hypersensitivity - Rashes, serum sickness (sunlight UV makes rash worse) GI disturbances Renal damage (crystalluria) Potentiate action of other drugs - Inhibit CYP2C9 ```
46
Trimethoprim | Mechanism:
Inhibits folate synthesis in bacteria by competitively inhibiting dihydrofolate reductase - Dihydrofolate analog
47
Trimethoprim Uses: | TMP/SMX combination:
Usually in combination with sulfamethoxazole: - Synergistic effect - 2 static drugs = 1 cidal combination TMP/SMX combination: - First choice therapy for uncomplicated UTIs - Upper respiratory tract ear infections (H. influenzae, Moraxella, Strep. pneumoniae) - GI infections (Salmonella, Shigella) - Pneumocystis jiroveci - 1st choice treatment and prophylaxis
48
TMP/SMX side effects
All of the other sulfonamide side effects Trimethoprim adds: - Nausea, vomiting, diarrhea, rashes - Bone marrow suppression * side effects especially pronounced with long-term use (AIDS)
49
``` Drug selection Prophylactic: Empiric: Pathogen-directed: Susceptibility-guided: ```
Prophylactic: Based on predominant flora at site of interest Empiric: Which drugs have good activity against most common pathogens Pathogen-directed: Which drugs likely target this pathogen Susceptibility-guided: susceptibility results
50
Empiric Diagnosis: Diagnostic Steps
1) Obtain culture/diagnostic tests 2) Empiric therapy 3) Diagnostic results - sensitivity profile 4) Modify therapy as needed 5) Cure
51
Once common use of empiric therapy
Uncomplicated cystitis in nonpregnant women | - 1st choice: TMP-SMX
52
Reasons for Antibacterial Failures
``` Drug Choice - Susceptibility of pathogen - Site of infection Host Factors - Do abscesses need draining - Immune response OK - Are there foreign bodies, implants, mechanical devices, indwelling lines ```
53
Widespread overuse of antibacterials has led to...
- Large numbers of antibiotic resistant strains - Ever-increasing need for new drugs - >50% of us carry multiply-resistant strains
54
CDC 2013 - Urgent threats
C. Difficile - Rapid increase in hypertoxigenic strains assoc. with antibacterial use N. gonorrhoeae - Ceftriaxone is the only agent left (use with either doxycycline or azithromycin) Carbapenem-resistant Enterbacteriaceae - Resistant to most drugs including carbapenems
55
CDC 2013 - Serious threats
``` Multi-drug resistant Acinetobacter Multi-drug resistant Pseudomonas Aeruginosa Drug-resistant Campylobacter ESBL gram negs (extended-spectrum β-lactamases) Salmonella/Salmonella Typhi Strep Pneumoniae VRE (Vancomycin-resistant Enterococcus) MRSA ```
56
Drugs for MRSA Hospital-acquired: Community-acquired:
``` Hospital-acquired: - Vancomycin - Linezolid - Daptomycin - Tigecycline Community-acquired: - Linezolid - Doxycycline, minocycline - Clindamycin - TMP-SMX ```

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