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PHRM 865 > Macrolides - SOA > Flashcards

Macrolides - SOA Flashcards

1
Q

List the macrolides:

A
  • erythromycin
  • azithromycin
  • clarithromycin
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2
Q

What is the mechanism of the macrolides?

erythromycin, clarithromycin, azithromycin

A

Macrolides inhibit protein synthesis by binding to the 50S ribosomal subunits.

Binding to the 50S ribosomal subunit induces dissociation of peptidyl transfer RNA from the ribosome during the elongation phase so that protein synthesis is suppressed and bacterial growth is inhibited

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3
Q

What kind of activity do macrolides display?

erythromycin, clarithromycin, azithromycin

A

Time-dependent, bacteriostatic

Azithromycin may be concentration depended against some organisms

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4
Q

What are the mechanisms of resistance to macrolides?

erythromycin, clarithromycin, azithromycin

A
  • active efflux out of the bacteria – coded by mef
  • alteration in the binding site via methylation – coded by erm

  • active efflux confers low level resistance
  • methylation of binding site confers high-level resistance
  • cross-resistance is usually observed among the macrolides
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5
Q

What is the general spectrum of activity for the macrolides?

erythromycin, clarithromycin, azithromycin

A
  • cover some GP (clarithro is the best of them for GP)
  • cover whimpy GN (azithro is the best of them for GN)
  • cover some atypicals
  • cover ADA
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6
Q

Which target organisms do the macrolides cover?

erythromycin, clarithromycin, azithromycin

A
  • MSSA
  • legionella

  • Primary agents for legionella
  • also cover mycobacterium avium complex
  • Azithro and clarithro are better for legionella and mycobacterium
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7
Q

Describe the absorption of the each of the macrolides:

A
  • erythromycin has to be enteric coated – it is not acid stable
  • clarithromycin is well absorbed regardless of the presence of food
  • azithromycin is decently absorbed regardless of the presence of food
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8
Q

Describe the distribution of the macrolides:

erythromycin, clarithromycin, azithromycin

A
  • the macrolides have a high volume of distribution
  • extensively distribute into tissues and cells
  • do NOT go into CSF

  • they achieve higher tissue concentrations than serum concentrations –> ineffective for bacteremia
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9
Q

How is erythromycin eliminated?

A
  • eliminated in the bile and liver by CYP450 enzymes
  • small percentage is excreted in the urine
  • NO dosage adjustment is necessary
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10
Q

How is clarithromycin eliminated?

A
  • metabolized in the liver by CYP450 enzymes
  • parent drug and metabolites are all excreted in the urine
  • dosage adjustment necessary in patients with CrCl < 30 mL/min
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11
Q

How is azithromycin eliminated?

A
  • Azithromycin is eliminated unchanged through biliary excretion
  • Azithromycin has a half-life of 68 hours
  • Azithromycin is NOT involved with CYP450
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12
Q

Which macrolide does not undergo CYP450 interactions?

A

Azithromycin is not metabolized and does not undergo CYP450 interactions.

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13
Q

Are any of the macrolides removed during hemodialysis or peritoneal dialysis?

A

No

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14
Q

Which macrolide requires dosage adjustment in renal dysfunction?

A
  • clarithromycin
  • dosage adjustment is necessary in patients with CrCl< 30 ml/min
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15
Q

What are the macrolides used for clinically?

A
  • respiratory infections
  • community acquired pneumonia
  • chlamydia (azithromycin)
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16
Q

What are the adverse effects from the macrolides?

erythromycin, clarithromycin, azithromycin

A
  • GI
  • thrombophlebitis and infusion site irritation
  • QT prolongation

Rare, but high dose IV erythro can lead to ototox in pts with renal insufficiency

17
Q

Which patients should macrolides be used in caution with?

A

Macrolides should be used in caution in patients with:
- hypokalemia
- history of Torsades or QT prolongation
- concomitant use of QT prolonging drugs (amiodarone, sotalol)

macrolides cause QT prolongation

18
Q

How can thrombophlebitis be avoided when using IV erythromycin and azithromycin?

A
  • dilute the dose in at least 240 mL of IV fluid
  • infuse slowly over 60 minutes
  • use a large vein
19
Q

Which macrolides are inhibitors of CYP3A4 and 2C9?

A
  • erythromycin
  • clarithromycin
20
Q

Which drugs do erythromycin and clarithromycin increase the serum concentrations of due to their 3A4 and 2C9 inhibition?

A
  • carbamazepine
  • cyclosporine
  • digoxin
  • phenytoin
  • theophylline
  • valproate
  • warfarin
21
Q

Does the interaction between azithromycin and antacids or calcium containing foods impact azithromycin?

A
  • No
  • The interaction between them is clinically irrelevant.
22
Q

Which macrolide is least likely to interact with warfarin?

A

Azithromycin

PHRM 865 (22 decks)

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