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PR3151 CA1: Antibiotics (NUS Pharmacy) > 30S Ribosomal Subunit Inhibitors > Flashcards

30S Ribosomal Subunit Inhibitors Flashcards

1
Q

Name the 3 classes of 30S ribosomal subunit protein synthesis inhibitors and their agents

A

Tetracyclines - Tetracycline, Doxycycline, Minocycline

Glycylcycline - Tigecycline

Aminoglycosides - Gentamicin, Amikacin, Tobramycin, Streptomycin, Neomycin

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2
Q

Mechanism of Action of Tetracyclines

A

Enter the bacterial cell through passive diffusion and active transport

Concentrate intracellularly and bind reversibly to 30S subunit to prevent tRNA binding to A site of mRNA-ribosome complex

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3
Q

Tetracyclines are administered ______

A

Orally best on empty stomach

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4
Q

Counselling point on tetracycline administration

A

Avoid dairy products , antacids and supplements containing divalent and trivalent cations

Formation of non-absorbable chelates

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5
Q

Tetracycline distribution, binding and CSF penetration?

A

Concentrate in bile, liver, kidney, gingival fluid, skin

Bind to tissue undergoing calcification (teeth and bone)

Cross placental barrier and concentrate in fetal bones and dentition

Moderate CSF penetration (Doxy and Mino)

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6
Q

Spectrum activity of tetracyclines

A

Gram positive/negative, atypicals, spirochetes

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7
Q

Tetracyclines do not cover ________ and ___________

A

Proteus and Pseudomonas

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8
Q

Tetracyclines are eliminated by what route?

A

Tetracycline - Kidney

Doxycycline - Bile and Urine Unchanged

Minocycline - Extensive metabolism before excretion

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9
Q

Contraindications of Tetracycline in ________

A

Pregnancy

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10
Q

Indications of each tetracycline drug

A

Tetracycline - Atypicals (Chlamydia, Mycoplasma pneumoniae), Vibrio cholerae, Yersinia pestis (Causing Plague)

Doxycycline - Above, Acne vulgaris, Anthrax, CAP, MRSA skin/soft tissue infection, Rickettsial disease

Minocycline - Tetracycline resistant strains (Some), Severe Acne, RTI, Yersinia (Plague)

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11
Q

Why are glycylcyclines designed for? What is it structurally similar to?

A

To overcome tetracycline resistance (Efflux pump, Ribosomal protection)

Minocycline structurally related

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12
Q

Tigecycline is administered __

A

IV (Poor oral bioavailability)

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13
Q

Tigecycline distribution

A

Penetrates well into tissues

Low plasma concentrations (Poor option for bloodstream infections)

CSF concentrations about 10% of that in serum (uninflamed meningitis)

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14
Q

Tigecycline is eliminated by _____

A

Biliary fecal route

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15
Q

Dose reduction tigecycline is recommended in ________________

A

Severe hepatic dysfunction

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16
Q

Tigecycline is contraindicated in _________

A

Pregnancy

17
Q

Tigecycline has broad spectrum activity including which resistant strains?

A
  1. MRSA
  2. VRE
  3. Carbapenem resistant ESBL Gram negatives
  4. Multi-drug resistant streptococci
  5. Complicated skin/skin-structure infections (except DM foot), intra-abdominal infections, CAP
18
Q

What are the 7 ADRs of tigecycline and tetracycline?

A
  1. Gastric discomfort (Esophageal irritation) - Do not take immediately before sleep
  2. Calcified tissue discoloration and hypoplasia from deposition e.g. Gray teeth
  3. Hepatotoxicity
  4. Phototoxicity
  5. Vestibular dysfunction (Dizziness, vertigo, tinnitus)
  6. Renal side effects in renal impaired patient
  7. Superinfection CDAD
19
Q

Tetracyclines and tigecycline are contraindicated in which population?

A

Pregnancy, breastfeeding, Children < 8 years old

Caution in myasthenia gravis

20
Q

Aminoglycoside mechanism of action

A

Diffuse through aqueous porin channels of Gram negatives’ outer membrane

Active transport energy-dependent phase

Block formation of initiation complex and cause misreading of codons. Wrong aminoacyl tRNAs bind to A site without matching the codon present in mRNA at the position. This inhibits translocation

21
Q

Why are aminoglycosides rapidly bactericidal?

A

Cationic nature affects cell membrane causing fissures to form. Destruction of cell membranes destroy the bacteria

22
Q

Administration route of Aminoglycosides by ______________ except for _________

A

Parenteral route, Neomycin (Oral)

23
Q

Aminoglycoside distribution and consequence on dosing? How about CSF penetration?

A

Penetration into body fluids vary (Due to low distribution to fatty tissue, they dosed based on lean body mass, not actual body weight)

Poor CSF penetration

Cross placenta barrier and may accumulate in fetal plasma and amniotic fluid

24
Q

Aminoglycosides are cleared by what route? Dose adjustment needed?

A

Renal clearance; Yes for renal impairment

25
Q

Aminoglycoside spectrum activity and why?

A

Broad-spectrum (Gram positive and negative) - Effective against aerobes only due to the need for energy-dependent active transport into the cell

26
Q

Aminoglycoside usual indications and type of therapeutic regimen

A
  1. Gram negative infections (Enterobacterales, Klebsiella, E coli, Pseudomonas and multi-drug resistant microbes like MDR tuberculosis)
  2. Empiric therapy for serious infections (septicemia, complicated UTI, nosocomial RTI) followed by discontinuation upon microbe identification (e.g. by culture)
27
Q

Aminoglycosides are used in combination with _______ in order to ______

A

Cell wall active agent Beta Lactams;

Expand empiric spectrum, synergistic killing and prevent emergence of resistance

28
Q

When is prolonged use of AGs allowed?

A

Restricted to life-threatening infections

29
Q

Aminoglycosides are cleared ______ except for Neomycin which is cleared _____

A

renally unchanged; unchanged in the feces

30
Q

Which AG is the preferred choice against Pseudomonas?

A

Tobramycin

31
Q

Which AG is the widest antimicrobial spectrum AG?

A

Amikacin

32
Q

Which AG is more active against Gram-positive cocci than other AGs when used synergistically with Beta Lactams?

A

Gentamicin

33
Q

Which AG is primarily used in combination with tuberculosis agents?

A

Streptomycin

34
Q

Which AG is the most toxic and is used for bowel prep?

A

Neomycin

35
Q

Neomycin is contraindicated in ?

A
  1. The presence of intestinal obstruction
  2. History of hypersensitivity to Neomycin and other AG
  3. Ulcerative GI disease
36
Q

Why is Neomycin not given parenterally?

A

Due to severe nephrotoxicity risk

37
Q

4 ADRs of Aminoglycosides

A
  1. Ototoxicity (Deafness may be irreversible)
  2. Nephrotoxicity (Disrupt calcium mediated transport in proximal tubules)
  3. Neuromuscular paralysis (With concurrent neuromuscular blockers administered)
  4. Hypersensitivity (Skin rash, contact dermatitis)
38
Q

What to monitor in patients taking Aminoglycosides?

A
  1. Caution when using in renal impairment, hearing defects, myasthenia gravis
  2. Limit usage of other nephrotoxic drugs (Amphotericin B, Vancomycin, NSAID, neuromuscular blocking agents)
  3. TDM - Peak and trough levels
  4. Renal function - Urea, creatinine, electrolytes
39
Q

4 types of resistance mechanisms against aminoglycosides

A
  1. Efflux pump increase
  2. Inactivating enzymes produced (e.g. to acetylate AGs)
  3. 30S ribosomal subunit alteration
  4. Uptake inhibition

PR3151 CA1: Antibiotics (NUS Pharmacy) (11 decks)

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