Macrolides and Ketolides – Bacterial Protein Synthesis Inhibitors (Antibiotics)

by Pravin Shukle, MD

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    00:00 Let's move on to the macrolides antibiotics.

    00:03 These macrolides antibiotics are very important group of medications because we use them all the time.

    00:08 Specially in respiratory infections.

    00:11 Now these agents are blocking the 50 S unit from transcription.

    00:15 Important agents include erythromycin and clarithromycin.

    00:19 They're rapidly eliminated from the body.

    00:22 They're considered broad spectrum antibiotics.

    00:25 And as I said before they're most commonly used in respiratory infections.

    00:29 Azithromycin concentrates into macrophages and other tissues and it is actually eliminated quite slowly.

    00:37 This particular medicine also effective in gonarrhea.

    00:41 The nice thing about azithromycin is that you can actually give it as a three day set of medications but it will last for ten days.

    00:48 So the killing activity actually lasts much longer than the drug is actually in the body.

    00:55 Other medications are more narrow spectrum within this drug group.

    00:59 The selectivity targets are generally gram positive anaerobes and aerobes.

    01:04 And these are used often in clostridium difficile infections.

    01:10 Let's talk about the resistance to macrolides antibiotics.

    01:14 It's actually quite an interesting topic because of the mechanism and the resistance patterns.

    01:20 Now you actually will develop ejector pump mechanisms in some bacteria that literally pump out the drug, the active drug out of the cell.

    01:28 It's quite an interesting phenomenon.

    01:30 The other thing that may happen in resistance patterns is changing the binding site of the macrolide by perhaps adding a methyl group.

    01:38 Now the problem here is that there is a 100% cross resistance pattern between one macrolide and another.

    01:45 So if for example you give a patient clarithromycin for a respiratory infection on week 1, they come back with resistance and you decide to try a different medication, there's going to be cross resistance between those two, say between clarithromycin and azithromycin.

    02:01 There's partial cross resistance with drugs like clindamycin and the streptogramins as well.

    02:08 And the resistance in the enterobactriaceae species and that is due to the production of drug destroying esterases.

    02:16 Not because of the ejector pump.

    02:19 So it's a slightly different mechanism but still 100% cross resistant pattern.

    02:29 Let's move on to the ketolides.

    02:31 Now the ketolides are structurally similar to the macrolides.

    02:35 And I haven't put a separate triangle here.

    02:37 Let's just say that that triangle is both for K and M.

    02:40 It has the same mechanism of action and the same antibiotic spectrum as the macrolides as well.

    02:46 Now a lot of times macrolides resistance strains are susceptible to the ketolides.

    02:51 And there is an increase affinity to the ribosomes with the ketolides than with the macrolides.

    02:56 They are also poorly ejected through ejector pores which is why we think these maybe really good choice for some people.

    03:05 So they sound very similar to the macrolides.

    03:08 They're used in community acquired pneumonia.

    03:11 They're nice because they are given once a day and they are oral medications.

    03:15 Downside.

    03:16 They can act through cyctochrome 3A4 and they do prolong the QT interval on the ECG which potentially could mean that they could be proarrhythmic.

    About the Lecture

    The lecture Macrolides and Ketolides – Bacterial Protein Synthesis Inhibitors (Antibiotics) by Pravin Shukle, MD is from the course Antimicrobial Pharmacology. It contains the following chapters:

    • Macrolides
    • Ketolides

    Included Quiz Questions

    1. Telithromycin
    2. Doxycycline
    3. Fidaxomicin
    4. Erythromycin
    5. Clarithromycin
    1. Drug-destroying esterases
    2. Ejector pumps
    3. Potentiation of CYP450 enzymes
    4. Beta-lactamases
    5. Adding a methyl group to change the binding site
    1. It is used in clostridium difficile infections.
    2. It is eliminated slowly.
    3. It is effective against gonorrhea.
    4. It has a potent post-antibiotic effect.
    5. It concentrates in macrophages and tissues.

    Author of lecture Macrolides and Ketolides – Bacterial Protein Synthesis Inhibitors (Antibiotics)

     Pravin Shukle, MD

    Pravin Shukle, MD

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