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Pharmacology > Aminoglycosides > Flashcards

Aminoglycosides Flashcards

1
Q

What are aminoglycosides❓

A

Antibiotics that contain amino sugars in glycosidic linkage

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2
Q

What are the properties of aminoglycosides❓

A

They are:

Polar cations

Not adequately absorbed after oral administration

Inadequate conc found in CSF

Relatively rapidly excreted

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3
Q

List some examples of aminoglycosides

A 
Gentamicin
Tobramycin 
Amikacin 
Netilmicin 
Kanamycin 
Streptomycin 
Neomycin
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4
Q

What are aminoglycosides used in treating❓

A

Primarily gram-negative bacterial infections

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5
Q

How could antimicrobial resistance be brought about❓

A

Aminoglycoside in the periplasmic space may be altered by microbial enzymes that phosphorylate adenylate or aceytylate specific hydroxyl or amino groups

Altered aminglycosides:
🚫bind effectively to ribosomes
🚫interfere with protein synthesis

Plasmids play a role in spread of resistance to other antibiotics

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6
Q

What are the limitations of aminoglycosides❓

Which aminoglycosides impact auditory function more❓

Which aminoglycosides have predominant vestibular effects❓

A
  1. Ototoxicity (*older patients are more susceptible)
    Nephrotoxicity
    Dysfunction of optic nerve
    Peripheral neuritis
    Neuromuscular blockade (⬆️dose of intraperitoneal/pericardial instillations)
  2. Amikacin
    Kanamycin
    Neomycin
  3. Streptomycin
    Gentamicin

*Tobramycin affect both equally

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7
Q

Streptomycin was first isolated from which organism❓

In what year❓

A

Streptomyces griseus

1943

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8
Q

Gentamycin and netilmicin are from species of which organism❓

A

Actinomycete micromonospora

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9
Q

Describe the chemistry of aminoglycosides

A
  • Hexose or aminocyclitol nucleus (usually in the center)
  • H/A Nucleus is either streptidine (streptomycin) or 2-deoxystreptocine (all other aminoglycosides)
  • 2/more aminosugars joined by a glycosidic linkage to the nucleus
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10
Q

What is the mode of transport of aminoglycosides❓

A

Transport/Phase 1/Energy Dependent state:

Diffusion through aqueous channel formed by porin proteins in the outer membrane of gram-negative bacteria
⬇️
Periplasmic space
⬇️
Generation of energy (membrane potential) to drive permeation of aminoglycosides into inner membrane

⬇️EDPhase2
Aminoglycosides bind to polysomes
⬇️
Inhibit the synthesis of proteins

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11
Q

Describe the mode of action of aminoglycosides

A

Rapidly bactericidal

Disrupt normal cycle of ribosomal function

Interfere w 1st step of protein synthesis

Cause accumulation of abnormal initiation complexes/streptomycin monosomes

Cause misreading of genetic code of mRNA template to produce incorrect proteins

⬇️translation of mRNA

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12
Q

What are the inhibitors of aminoglycoside transport in bacteria❓

How is relevant in practice❓

A 
1.
Divalent cations eg Ca2+
Hyperosmolality
⬇️pH 
Anaerobic environment

*impair the ability of bacteria to maintain membrane potential required for the transport of aminoglycosides

  1. Antimicrobial activity is markedly ⬇️ in anaerobic conditions or hyperosmotic acidic urine eg liver abscess
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13
Q

The intracellular site of action of the aminoglycosides is the _____ribosomal subunit

What does it comprise❓

What is the relevance of this❓

A

30s
50s (other A. apart from streptomycin)

21proteins
A single 165 molecule of RNA

Alteration of at least 3 of these proteins affect the action of streptomycin

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14
Q

What are the factors that could be responsible for antimicrobial resistance to aminoglycosides?

A

Inactivation of the drug by bacterial enzymes

Failure of permeation of antibiotics

⬇️affinity of the drug for bacterial ribosome

Oxygen-deprived infections

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15
Q

The antibacterial activity of aminoglycosides is mainly against gram negative bacilli

True or false

A

True

Action against gram positive bacteria is limited

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16
Q

Gentamicin and tobramycin are active invitro against >95% strains of staphylococcus aureus

True or false
Should they be administered alone❓

A

True

No

17
Q

What are sensitive microorganisms❓

A

Microorganisms inhibited by peak conc. of antibiotics that can be achieved clinically in plasma but that are not associated with ⬆️toxicity

4-8❓/ml for gentamicin, tobramycin and netilmicin

8-16 ❓/ml for amikacin and kanamycin

18
Q

Which aminoglycosides have retained their activity against nosocomial infections❓

Why❓

A

Amikacin
Netilmicin

Resistance to aminoglycoside metabolizing enzymes

19
Q

What can cause a ⬇️absorption of aminoglycosides❓

Absorption of Neomycin is not altered in the presence of inflammatory bowel disease. True or false

A

Bacilliary dysentery

True

20
Q

What could cause an accumulation of aminoglycosides❓

A

Renal impairment

Instillation into body cavities with serosal surfaces

Topical application to large wounds or cutaneous ulcers

21
Q

A rapid absorption of aminoglycoside should be expected with what form of administration at what time intervals❓

A

IM/SC injection:
Peak plasma conc. -30-90min

IV injection:
Peak plasma conc -30min

22
Q

Describe the distribution of aminoglycosides

What is the volume of distribution❓

A
  1. Excluded from most cells, CNS and the eye due to polarity

⬇️conc. in secretions and tissues

⬆️conc. in renal cortex (Nephrotoxicity)

⬆️conc in endolymph, perilymph of inner ear (Ototoxicity)

2.
25% of body weight, approx. the volume of ECF

23
Q

Inflammation could ⬆️ the penetration of aminoglycosides into peritoneal and pericardial cavities

True or false

A

True

24
Q

How would you administer aminoglycosides to an adult with gram negative bacillary meningitis❓

A

Intrathecal ad

OR

Intraventricular ad.

*Not needful in neonates who have immature BBB

25
Q

What is the half life of aminoglycosides❓

A

2-3hours in plasma

26
Q

How are aminoglycosides excreted❓

What is usually the conc. In urine❓

What is the renal clearance❓
What does this suggest❓

A

Glomerular filtration

50-200❓g/ml

2/3 of simultaneous creatinine
Tubular reabsorption

27
Q

A large fraction of parenterally admin doses of aminoglycosides is excreted unchanged during the 1st 24hours with most of this appearing in the 1st 12hrs

True or false

A

True

28
Q

A lineal relationship exists between the conc. of creatinine and half-life of aminoglycosides in pt with moderately compromised renal function

True or false

A

True

29
Q

The incidence of nephro and ototoxicity is related to conc of aminoglycosides

What is the significance of this in treatment❓

A

⬇️maintenance dosages in pt with impaired renal function with precision

30
Q

Which pt are more susceptible to neuromuscular blockade of aminoglycosides❓

A

Pts w mysthenia gravis

31
Q

What is the Rx for aminoglycoside toxicity❓

A

Ca2+ salt

32
Q

Streptomycin as dry powder/solution 400-500mg/ml

What would you use it in treating❓

How can it be administered❓

A 
1.
Tuberculosis endocarditis 
D-streptococci 
Oral streptococci of viridians grp
Enterococcal endocarditis(+Peni. G)
Brucellosis 
2.
IM injection (painful),

Duration: 7-10/7days
6months for TB

Amount : 1-2g
15-25mg/day divided into 2 doses per day

33
Q

Gentamycin as ointment, cream, ophthalmic prep. and prefilled syringes 10mg/ml, 40mg/ml, 240mg/2ml or 280mg/2ml

What would you use it in treating❓

How can it be administered in neonates❓

A
  1. UTI (combination therapy)

Pneumonia, esp pseudomonas aeruginosa (CT)

Combination therapy in sepsis

  1. 6mg/kg daily- 2 equally spaced injections
34
Q

What would you use tobramycin in treating❓

How can it be administered❓

Is tobramycin similar to gentamycin in antimicrobial activity and pharmacokinetics❓

A 
1.
Pseudomonas aeruginosa 
Bacterimia
Osteomyelitis 
Pneumonia
  1. SO4 salt, parenterally
    40mg/ml IM or IV
  2. Yes
35
Q

Amikacin has a special role in hospitals where gentamicin and tobramycin resistant microorganisms are prevalent.

Why❓
What is amikacin used for❓

A

It has the broadest antimicrobial activity and is useful when there is resistance to aminoglycosides

36
Q

Netilmicin is not metabolized by majority of the aminoglycoside-metabolizing enzymes.

True or false❓
What is the significance of this❓

A

True

May be active against bacteria that are resistance agains gentamycin

37
Q

What is kanamycin commonly used for❓

What is it’s drawback❓

A

Used in combination therapy for treating TB when microorganisms are resistant to the more commonly used agents

Involves administration of ⬆️doses w risk of ototoxicity and nephrotoxicity

38
Q

Neomycin

  1. What is it known for❓
  2. How can it be administered❓
  3. What can it be used in treating❓
  4. What are it’s drawbacks❓
A
  1. Broadspectrum antibiotic
  2. Tropical/oral/parenteral preparation
  3. Bowel preparation for surgery
    Adjunct to therapy of hepatic coma
    Rx in burns/wounds/ulcers
  4. Hypersensitivity (6-8% pt), topically
    Malabsorption
    Superinfection

Pharmacology (10 decks)

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