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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 50S unit from translation.

    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.

    02:25 Let's move on to the ketolides.

    02:26 Now the ketolides are structurally similar to the macrolides.

    02:30 And I haven't put a separate triangle here.

    02:32 Let's just say that that triangle is both for K and M.

    02:35 It has the same mechanism of action and the same antibiotic spectrum as the macrolides as well.

    02:41 Now a lot of times macrolides resistance strains are susceptible to the ketolides.

    02:46 And there is an increase affinity to the ribosomes with the ketolides than with the macrolides.

    02:51 They are also poorly ejected through ejector pores which is why we think these maybe really good choice for some people.


    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. Ejector pumps
    2. Decreased wall permeability
    3. Gene transfer
    4. Modification of binding site
    5. Esterases
    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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