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Beta-Lactam Antibiotics: Classifications and Mechanism of Action (Nursing)

by Rhonda Lawes

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    00:01 Hi. Welcome to our video on Beta-lactam antibiotics, or you probably know them by their name, penicillins.

    00:09 So, this would be the 1 group of medications you probably have already been exposed to or even taken yourself before you started your nursing program.

    00:17 Let's roll into these drugs and how we use them in a setting.

    00:20 Now. they're called Beta-Lactam Antibiotics because of the ring that they have.

    00:25 See that the drug on the left, penicillin, and the other drug, cephalosporins, they have a Beta-lactam ring.

    00:32 Now, don't get worried.

    00:34 We're not going to ask you to draw the chemical formulas or molecules for these drugs.

    00:38 I just wanted you to understand why they're called Beta-Lactam Antibiotics.

    00:43 Now there's 4 major sub-classes of Beta-lactam antibiotics.

    00:48 There's penicillins, cephalosporins, carbapenems, and monobactams.

    00:56 Now, the reason that you care about this is because Beta-lactam antibiotics have the small chance of having cross allergies.

    01:04 So, if a patient is allergic to penicillin, there's a very small chance, like < 5% chance, that they would have a cross allergy to a cephalosporin.

    01:14 So, in an NCLEX test question and like we say, in NCLEX world, if I know my patient has a penicillin allergy, then I also would not want to give them a cephalosporin.

    01:25 Now, let me give you an example of how a test question may come up.

    01:28 You may see something that says, "Your physician has the following orders for your patients.

    01:33 Which one of the orders requires immediate follow up?" Well, if I knew my patient had a penicillin allergy and they had listed any cephalosporins in the answer choices, that would be the one I would go for. Because they both have Beta-lactam rings, and even though there is a very small chance that there could be a cross allergy, in NCLEX world, we wouldn't give that drug, and that's why we would contact the healthcare provider.

    01:59 So, let's start talking about the penicillins.

    02:02 If you've watched our other video on sulfonamides, you know that they were introduced in the 1930s.

    02:07 Now, penicillins came along in the 1940s and these really were a game changer.

    02:14 Now they're bactericidal.

    02:16 Remember, that's a cell killer that kills those bacteria, and how they do that is they inhibit cell wall synthesis.

    02:23 So, if that cell wall isn't complete and intact, that bacteria is going to die.

    02:28 But penicillins are active only against bacteria that are undergoing growth and division, so we've got to get that drug in there, and they can attack when the cell is undergoing growth and division.

    02:39 Now, penicillins are broad spectrum, so they kill a wide variety of bacteria.

    02:45 emember, our goal is to try and keep you on the most narrow spectrum to help deal with microbial resistance.

    02:51 Now, you'll see the picture of the inventor of penicillin there, we thought we'd give him a little shout out, a little props as we're going through this.

    02:59 There's some classifications of penicillins.

    03:01 The first 2 deal with the narrow spectrum penicillins, and 1 group of them, penicillinase sensitive, and the other group is penicillinase resistant.

    03:12 So I've got examples of the drug names there for you.

    03:15 Penicillin G and penicillin V are penicillinase sensitive.

    03:21 That means that they're not very good in treating those bugs because the penicillinase destroys them.

    03:26 I'll talk to you a little bit more about that later, but just kind of get in your mind we have narrow spectrum penicillins.

    03:33 Some are sensitive to the enzymes penicillinase, and some are resistant to those enzymes.

    03:40 Obviously, 1 of the drugs, the nafcillin, oxacillin, or dicloxacillin is going to be our choice because it's penicillinase resistant.

    03:49 Now, I'll explain why that sounds different than we're looking at culture and sensitivity in just a minute.

    03:53 Now, the third and fourth groups deal with broad-spectrum penicillins and extended-spectrum penicillins.

    04:00 So, broad-spectrum penicillins are like ampicillin or amoxicillin, and lots of times, you see these prescribed for pediatric patients.

    04:07 Piperacilin is an even more extended spectrum.

    04:11 So when we're looking at the classifications of penicillins, I want you to, kind of, have just in mind, for frame of reference, 4 variables: narrow spectrum, penicillinase sensitive, penicillinase resistant, broad-spectrum, and extended- spectrum penicillins.

    04:28 Okay, so let's look at that mechanism of action.

    04:31 You'll see in your notes that you have that little icon that will remind you that the mechanism of action is it weakens the bacterial cell wall.

    04:40 So, use that as a little trigger for your brain to remember that that is the mechanism of action of these medications.

    04:46 So, the penicillin enter the bacteria through their cell wall.

    04:49 Now, once the penicillin gets inside that cell, they bind to penicillin-binding protein.

    04:56 Yay. Just stop for a minute and celebrate something -- its name, so it makes perfect sense on what it does.

    05:02 Penicillin-binding proteins bind with the penicillin once it's inside the wall, and then once they're bound, that cell wall synthesis becomes abnormal, it's disrupted.

    05:14 Well, that might not sound like such a big deal to you, but it's a big deal because when you disrupt normal cell wall synthesis, the bacteria cells will die from – boom -- cell lysis.

    05:27 So, penicillins don't kill other cells in the body, but they sure take care of business with the bacteria.

    05:34 So, walk through that with me again 1 more time.

    05:37 I give my patient penicillin.

    05:38 Penicillin will actually enter the bacteria through the cell wall.

    05:42 Then the penicillin will bind with the penicillin-binding proteins, and once it's bound, that cell wall isn't complete anymore, and they end up with lysis. All of the good stuff squishes out of the bug and it's dead.

    05:57 And that's why penicillin is considered a bactericidal antibiotic.

    06:02 Okay, now. We've put together some really cool things to help you remember the key points about penicillin.

    06:08 Look at the P.

    06:10 They penetrate the cell wall and they're protein binding.

    06:14 That's awesome. So, you've got step 1 and step 2 right there.

    06:17 P for penicillin, penetrate, and protein-binding.

    06:22 Then look at the C. It makes the cell wall weak and leaky.

    06:28 And L, causes a lysis of the cell.

    06:31 So this kind of method works for your brain and I encourage you to put a circle by this or star this to know that penicillin penetrates the cell wall, protein binds, then the cell wall becomes weak and leaky, and there's a lysis of the cell.


    About the Lecture

    The lecture Beta-Lactam Antibiotics: Classifications and Mechanism of Action (Nursing) by Rhonda Lawes is from the course Anti-Infective Drugs in Nursing. It contains the following chapters:

    • Classifications of Penicillins
    • Penicillins: Mechanism of Action

    Included Quiz Questions

    1. Penicillin
    2. Cephalosporins
    3. Carbapenems
    4. Monobactams
    5. Macrolides
    1. Penicillin G
    2. Nafcillin
    3. Oxacillin
    4. Ampicillin
    1. Disrupts bacterial cell wall synthesis
    2. Prevents bacterial cell replication
    3. Inhibits production of bacterial enzymes
    4. Induces programmed cell death
    1. Cell wall
    2. Periplasmic space
    3. Plasma membrane
    4. Capsule

    Author of lecture Beta-Lactam Antibiotics: Classifications and Mechanism of Action (Nursing)

     Rhonda Lawes

    Rhonda Lawes


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