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Classes of Antibiotics and Mechanisms of Action

ß-Lactams. What are some of the classes of antibiotics and how do they work? I already mentioned beta-lactams. They inhibit the bacterial peptidoglycan (cell wall). That's why penicillin is so safe. Peptidogycan is not a component of any of your cells. That's what we look for when we look for an antimicrobial agent. Some target that is unique to bacterial pathogens (disease producers) that we can hit that won't hit your cells. That's why penicillin hitting its select target, is a very, very safe drug. Cephalosporins, they're also beta-lactams. Penicillin V, you may be familiar with that. If you have a strep throat and there has been some concern about resistance in your particular community, you might get it. Certainly physicians and dentists use this a lot, by the way. When dentists extract the large molars, you can get an infections. That's why antibiotics are usually used prophylactically. Also, anyone that has heart valve problems or has a heart valve replacement, when they go to a dentist, they are prescribed one of these drugs prior to their visit. They use it prophylactically so those creatures that I talked about getting into the blood are prevented from doing so. This use reflects the concern about subacute bacterial endocarditis.

Augmentin is a special one which contains a component that can actually block the enzyme that destroys beta-lactams. Macrolides (such as Zithromax or erythromycin) work by inhibition of protein synthesis, bacterial protein synthesis. Here are some examples. Tetracycline also works by inhibition of protein synthesis. Quinolones, these are purely synthetic. They were not found in nature anywhere. They're made synthetically. They have direct action against bacterial DNA gyrase as well as topo isomerase IV. Well, so what? What does that mean to you, right? Gyrase? That's an important function in the bacterial cell where it actually twists the double stranded DNA. It really gives them a hyper coil. What I don't have on this slide is a topo isomerase-IV. In order for the strand to pass through and unwind, you actually have to have a cut in the DNA and then a passage of a strand through the DNA that's cut to open up the DNA so it can be a reproduced and the polymerase can take its action. There are some examples here. This is Pfizer's (trovafloxacin). By the way, notice that I don't have Pfizer on any of my slides. It's coming up though. That was my own choice. I was not directed to do so but I just figured I'm on my own on this thing. Pfizer can sell their products. I'll go out and I'll talk and represent them. But this is not a commercial for Pfizer.

Aminoglycosides, again, inhibition of protein synthesis. They are commonly used in urinary tract infections. Women particularly very frequently have a problem with urinary tract infection. This is one of the groups that can be used although there are problems of human toxicity sometimes. Clorhexadine, which I don't know if it's approved in the US. I guess it is approved now under prescription by dentists. It's a surfactant that destroys the bacterial membrane. It's extremely useful in controlling those peridontal organisms. It does it extremely well. In Europe, in fact, they have mouthwash where you just swish and the stuff would stick to your tooth's surface. It really did a pretty good job prophylactically, even therapeutically. It does cause tooth discoloration though and there may be other difficulties with it.


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