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CPRS > L71: Drugs Used in the Treatment of Pulmonary Infections > Flashcards

L71: Drugs Used in the Treatment of Pulmonary Infections Flashcards

1
Q

URT infection

A
  • pharyngitis/sore throat
  • tonsillitis
  • sinusitis (inflammation of mucous membrane of sinuses)
  • otitis media (inflammation of mucous membrane of middle ear)
  • cold/flu
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2
Q

LRT infection

A
  • Acute bronchitis (RSV, parainfluenza virus, adenovirus)
  • Acute bronchiolitis (terminal bronchioles, RSV, parainfluenza virus)
  • Pneumonia (bacterial infections)
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3
Q

***Drugs used in pneumonia

A

Beta-lactams:

  1. Penicillin +/- betalactamase inhibitor (cell wall synthesis)
  2. Cephalosporin (cell wall synthesis)

Protein synthesis inhibitors:

  1. Macrolide (50s inhibitor, increasing resistance)
  2. Tetracycline (30s inhibitor)

Nucleic acid synthesis inhibitors:
5. Fluoroquinolone (DNA gyrase + topoisomerase IV, gram -ve)

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4
Q

Members of beta-lactam antibiotics

A
  1. Penicillin (narrow/extended spectrum)
  2. Cephalosporin (1st -5th gen)
  3. Carbapenem
  4. Monobactam
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5
Q

Mechanism of beta-lactam antibiotics

A

BacterioCIDAL

Mimics structure of D-Ala-D-Ala link
—> covalently bind to and inhibit transpeptidase/penicillin binding protein (PBP)
—> inhibit pentapeptide cross linking between NAM subunits
—> bacterial cell wall weakens
—> autolysin activated to destroy existing cell wall / osmotic lysis

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6
Q

Gram +ve vs Gram -ve bacteria in relation to drug actions

A

Gram -ve: LPS —> drugs need Porin channel to be actively transported into bacteria

Gram +ve: drugs go in by simple diffusion

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7
Q

Mechanisms of resistance to beta-lactam

A

Gram +ve:

  1. Beta-lactamase
  2. Altered PBP / transpeptidase

Gram -ve:

  1. Loss of porin channels
  2. Efflux pump
  3. Beta-lactamase
  4. Altered PBP / transpeptidase
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8
Q

Classification of penicillins

A
  • Narrow spectrum, Beta-lactamase sensitive
  • Narrow spectrum, Beta-lactamase resistance
  • Extended spectrum aminopenicillin
  • Extended spectrum antipseudomonal penicillin
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9
Q

Narrow spectrum, Beta-lactamase sensitive

A 
Penicillin G
Bad:
- Narrow spectrum
- Beta-lactamase SENSITIVE
- acid labile
- short duration
- poor penetration into CNS
- allergy

Adverse effects

  • Diarrhea
  • Seizure
  • Low toxicity
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10
Q

Narrow spectrum, Beta-lactamase resistance

A

Antistaphylococcal penicillin

  1. Methicillin (too nephrotoxic)
  2. Flucloxacillin

Good

  • Beta-lactamase RESISTANT: for beta-lactamase resistant staphylococcal infection
  • acid stable

Bad

  • Narrow spectrum
  • poor penetration into cell membrane (due to bulky side chain)
  • less effective than other penicillin
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11
Q

Extended spectrum aminopenicillin

A
  1. Ampicillin
  2. Amoxicillin

Good:

  • Broader spectrum
  • Gram +ve
  • Gram -ve cocci and bacilli
  • acid stable
  • good oral bioavailability

Bad:

  • Beta-lactamase SENSITIVE
  • NOT active against Pseudomonas
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12
Q

Antipseudomonal penicillin

A

Carboxypenicillin: carbenicillin, ticarcillin
Ureidopenicillin: piperacillin

Good:

  • effective against gram -ve bacilli
  • effective against pseudomonas aeruginosa

Bad:

  • Beta-lactamase SENSITIVE
  • acid labile
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13
Q

Beta-lactamase inhibitor

A
  1. Clavulanate
  2. Sulbactam
  3. Tazobactam

Irreversible inhibitor of beta-lactamase

Combined with Broad-spectrum beta-lactam:

  • Augmentin: amoxicillin + clavulanate
  • Tazocin: piperacillin + tazobactam
  • Unasyn: ampicillin + sulbactam
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14
Q

Cephalosporin

A

BacteriCIDAL

MOA:
- covalently bind to PBP —> inhibit cell wall synthesis

Broad spectrum:

  • Gram +ve
  • Gram -ve
  • anaerobes
  • Beta-lactamase RESISTANT
  • non-toxic
  • hospital overuse
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15
Q

Classification of cephalosporin

A

1st gen: greatest activity vs Gram +ve
- cefalexin

2nd gen: expanded activity vs Gram -ve
- cefuroxime

—> Nowadays use 3rd gen onwards

3rd gen: mainly vs Gram -ve
- cefotaxime, ceftriaxone

4th gen: wide spectrum, beta-lactamase resistant
- cefepime

5th gen: wide spectrum, MRSA-active
- ceftaroline

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16
Q

Pharmacokinetics of cephalosporin

A
  • IV/IM due to poor oral absorption (except cefalexin, cefuroxime)
  • well-distributed in body fluids
  • inadequate CSF penetration except 3rd gen
  • long half life: once daily
  • renal excretion (except ceftriaxone: biliary excretion)
17
Q

Adverse effects and disadvantages

A
  • GI irritation (diarrhoea, nausea)
  • allergy (rare)
  • nephrotoxicity (infrequent)
  • very expensive (esp. parenteral preparations)
18
Q

***Protein synthesis inhibitor

A

BacterioSTATIC

Broad spectrum:

  • Tetracycline (30s)
  • Chloramphenicol

Moderate spectrum:

  • Macrolide (50s)
  • Ketolides

Narrow spectrum:

  • Linezolid (50s)
  • Lincosamides (Clindamycin)
  • Streptogramins
19
Q

Mechanisms of action of macrolide

A
  • Irreversible binding to 50S subunit
  • Inhibit translocation of polypeptide chain from A to P site by peptidyltransferase
  • block movement of peptidyl tRNA from A to P site
  • incoming tRNA cannot bind to A site
  • stop protein synthesis
20
Q

Spectrum of macrolides

A

Gram +ve: clarithromycin > erythromycin > azithromycin
Gram -ve: azithromycin > clarithromycin > erythromycin

Erythromycin (same as penicillin):

  • active vs Gram +ve
  • for patient allergic to penicillin

Clarithromycin:
- higher activity vs Intracellular pathogens (Chlamydia)

Azithromycin:

  • enhanced activity vs Gram -ve
  • less activity vs Gram +ve

Telithromycin (similar to azithromycin):
- effective vs macrolide-resistant strains

21
Q

Pharmacokinetics of macrolides

A
  • acid stable (except erythromycin —> enteric coating)
  • All well absorbed
  • well distributed in tissue
  • poor penetration into CSF
  • concentrated in phagocyte (useful vs intracellular pathogen)
  • Time-dependent post-antibiotic effect: long half life of azithromycin
  • conversion to active metabolite: all except erythromycin
  • clarithromycin excreted in urine
  • erythromycin + azithromycin excreted in bile
  • erythromycin + telithromycin extensively metabolised
22
Q

Good and Adverse effects of macrolide

A
  • Large therapeutic index
  • Non-toxic
  • GI disturbance (stimulation of motilin receptor)
  • Arrhythmia (QT prolongation)
  • Erythromycin: deafness (high dosage)
  • Drug interaction (inhibit CYP3A4 except azithromycin)
  • Caution with liver disease
  • Taking erythromycin estolate ester preparation for >1-2 weeks can cause cholestatic hepatitis (fever, abdominal pain, jaundice)
23
Q

Uses of macrolide and Resistance mechanism

A

Use

  • Penicillin substitute
  • Mycoplasma, Legionella pneumoniae
  • Empirical antibiotic for outpatient pneumonia

Resistance

  • Efflux pump (NOT for telithromycin)
  • 50S subunit modification by methylases encoded by “erm”
  • Esterase to hydrolyse macrolide
24
Q

Tetracyclines

A
  • BacterioSTATIC
  • Broad spectrum
  • inhibit protein synthesis (30S)
  • used for uncommon infections
  • resistance problem
  1. Doxycycline
    - Long duration of action
    - Good oral absorption
    - 20% reduced taken with milk/food (take on empty stomach)
    - Biliary excretion (for renal impaired patients)
25
Q

Mechanisms of action of tetracyclines

A

Bind to 30S
—> prevent access of amino acid tRNA to A site on mRNA-ribosome complex
—> block addition of amino acid to existing peptide chain
—> stop protein synthesis

26
Q

Glycylcyclines

A

Derived from tetracycline

  • IV infusion
  • effective vs multi-resistant Gram +ve
  • NOT effective vs Proteus + Pseudomonas spp.
  • Biliary excretion
  • for complicated intra-abdominal infections
27
Q

Adverse effects of tetracycline

A
  • Local tissue irritation
  • GI irritation
  • Hepatotoxicity
  • Teeth discolouration (avoid giving pregnant and under age of 8)
  • Photosensitation
  • vestibular problems
28
Q

Resistance mechanisms to tetracycline

A
  1. Impaired influx (Porin channel)
  2. Increased efflux
  3. Production of proteins that prevent binding to 30S
  4. Tetracycline-inactivating enzyme
29
Q

Quinolone

A

1st gen: Non-fluorinated

  • Nalidixic acid
  • urinary antiseptic, no systemic effect
  • effective vs Gram -ve causing recurrent UTI
  • resistance problem

2nd gen: Fluorinated (Fluoroquinolone)

  • Ciprofloxacin
  • expanded vs Gram -ve
  • some vs Gram +ve
  • NOT effective against anaerobes
  • for UTI, LRTI
  • resistance problem

3rd gen:

  • Levofloxacin
  • expanded vs Gram -ve
  • improved vs Gram +ve

4th gen:

  • Moxifloxacin, Gemifloxacin
  • maintained vs Gram -ve
  • improved vs Gram -ve
  • Anaerobic coverage
30
Q

Fluoroquinolone

A

BacterioCIDAL

  • Broad spectrum (esp Gram -ve)
  • Safe
  • Effective in LOWER RT infection
  • reserved for respiratory and urinary infections caused by resistant bacteria
  • Uncommon resistance
31
Q

Mechanism of action of fluoroquinolone

A
  1. Inhibit DNA gyrase (topoisomerase II)
    —> quinolone-DNA-gyrase complex
    —> induced cleavage of DNA
  2. Inhibit DNA topoisomerase IV
32
Q

Pharmacokinetics and Adverse effects of fluoroquinolone

A

Pharmacokinetics:

  • high tissue penetration
  • renal excretion

Adverse effects

  • GI symptoms
  • CNS symptoms (dizziness, confusion, insomnia)
  • photosensitivity
  • Ruptured tendons / Arthropathy (CI in children, pregnant and nursing women)
  • interaction with antacids
  • CYP450 inhibitor (warfarin, theophylline)
33
Q

Mechanisms of resistance to Fluoroquinolone

A
  1. Efflux pump (upregulation)
  2. Mutations of DNA gyrase / topoisomerase IV
  3. Reduced Porin channel (in outer membrane of gram -ve bacteria)
  4. Drug-modifying enzyme acetyltransferase
34
Q

Empirical antibiotic selection for CAP

A

Amoxicillin:
Good: S. pneumoniae
Bad: Atypical agents / beta-lactamase (add clavulanate)

Cephalosporins:
Good: most S. pneumoniae and ALL H. Influenzae
Bad: Atypical agents

Macrolide:
Good: most common pathogen including Atypical agents
Bad: resistance problem

Fluoroquinolone:
Good: H. influenzae, Atypical agents (mycoplasma), less vs S. pneumoniae
Bad: increasing resistance

35
Q

CDC recommendations in prescribing antibiotics

A
  1. Identify causative agent
  2. Susceptibility testing
  3. Give empirical —> then specific
  4. Appropriate dose and duration

CPRS (75 decks)

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