Antibiotic Prefixes and Suffixes

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Welcome to the Memorizing Pharmacology podcast. I'm Tony Guerra, pharmacist and author of the Memorizing Pharmacology book series, bringing you mnemonics, cases, and advice for succeeding in pharmacology. Sign up for the email list at memorizingfarm.com to get your free suffixes cheat sheet or find our mobile-friendly self-paced online pharmacology review course at residency.teachable.com/p/mobile. Let's get started with the show.

I've recorded penicillins and cephalosporins, but before I go on, I have to address antibiotic prefixes and suffixes. These can be really useful, but you can also fall into a number of mistakes because there are so many mistakes on the electronic note cards. I've contacted a couple of the companies and said, "Hey, you know, my stuff is up on your note cards. I don't care that my stuff is on your note cards. Well, I do, but what I really care about is that they're wrong."

And I know that it's a lot easier to use somebody else's note cards when you're on one of those websites, but you have no idea what grade they're getting in their class. You don't know if they're taking it again and they failed the class or what. So I want to go over prefixes and suffixes for 14 of the most common antibiotic prefixes and suffixes that will help you. But let me first define this term heuristic cognitive bias.

A heuristic is a shortcut. Someone who's making these note cards says, "Well, I saw penicillin, amoxicillin, ampicillin. They all end in -cillin. Therefore, all penicillin-class antibiotics end in -cillin." And we don't really teach logic anymore, and anyone going to college probably would take ethics instead of formal logic. So these errors I'm talking about have their names in formal logic, and I'm not going to get into that as much as just kind of explain the issue.

So they found that this was true, and what they did was say, "Well, here I am finding that -cillin has a shortcut for penicillins. Then I can make shortcuts for other drug classes." So here's where the cognitive bias comes in. The cognitive bias is the error from the shortcut. "Every antihistamine I've seen ends in -ine. Therefore, all antihistamines end in -ine." But diamohedronate is an antihistamine and that doesn't end in -ine.

So again, it's that cognitive bias that everything they had seen in their experience was -ine, so it must be right. And that's just not true. The real issue comes from the next step that they make. And again, I'm not going to go into the formal logic. But if all antihistamines end in -ine, then all drugs that end in -ine are antihistamines. Let's put that in online flash card and help other people.

Their intent is solid. They want to help other people by publicly posting their note cards. That's great. But they're just plain wrong. Morphine ends in -ine and that's an opioid. Fluoxetine ends in -ine and that's a selective serotonin reuptake inhibitor. Cephyroline is a cephalosporin and that ends in -ine.

What they're trying to do is they're trying to create a shortcut so they can make sense of pharmacology. And that's completely understandable. But the issue is that they're just wrong with the stems because they're not coming from a reliable source. And I can look pretty quickly at one of those note card sets and say, "Yep, that one's wrong," or "That one's right."

So what I want to do is go over the correct antibiotic prefixes and suffixes of the most common drugs, explain a little bit about some confusion between -mycin and -mycin, and then show you some of the errors that you're going to see, just to create an awareness of these antibiotic prefixes and suffixes and how you can use them, how you can rely on them, but where the pitfalls are, where you can't really use part of it. Okay, so the first one is ceph, the cephalosporins: cephalexin, ceftriaxone, cefepime, and cephyroline. So cephalexin, first generation; ceftriaxone, third generation with the tri; cefepime is that maxipeam, the fourth generation; cephyrholenus, fifth. And this is consistent. Okay. And it's common that penicillins and cephalosporins are two of the first drugs that a pharmacology teacher will teach because they affect the cell wall and they're related. Cyclin, this is a tetracycline type antibiotic. And sometimes you'll see them cut it off where they say l-i-n-e is what makes it tetracycline or just in. And those are both incorrect. So it has to have that cycline to make it a tetracycline class antibiotic. And again, tetra meaning four and then cyclin, four rings with organic chemistry. Floxacin, this is a fluoroquinolone. It's not going to be on the stem list. And I'll go into oxyacin in a little bit. The FL is actually a substem saying that there's a fluorine atom in there. And then the oxyacin is really what's telling you that it's a quinolone antibiotic. But this again is pretty consistent. So ciprofloxacin, levofloxacin, you can be pretty confident that it's going to be a fluoroquinolone. Casein, so an antibiotic obtained from the streptomyces canamyceticus and then related to canomycin. Or we have to be careful here is that we're saying okay casein comes in amication and we can say it's an antibiotic but we can't necessarily say it's a certain class of antibiotics. So amicasin just happens to be an amino glycoside but we're going to see in just a second that it might be an antibiotic but it doesn't necessarily tell you what class of antibiotic. So the ones that we had before though, the ceph for cephalosporin, bacillin for penicillin, the cyclin for tetracycline and then even the floxacin for fluoroquinolone, those were reliable for helping us know the class of antibiotic. But casein, this might not be one that we can do that with. And let me get to the next slide. Mycin is really a troublemaker. So mycin, the antibiotics coming from the micro monospora strains: you have gentamicin which is an amino glycoside but you have fedexamicin which is a macrolide. So already we see two completely different antibiotic classes with identical suffixes. So some of these suffixes will allow you to learn that it is an antibiotic and some will allow you to learn that it's an antibiotic and a specific class. It just depends. Okay? This mycin which many people pronounce as myosin, they insert an a vowel in there, it's actually difficult to pronounce this together. This comes from the streptomycy strain and clarithromycin is a macrolide; clindamycin is a lincosamide; and vancomycin is a glycopeptide. So the mycin isn't reliable for telling you the class that it comes from and I'll talk a little bit more about that t-h-r-o substem in clarithromycin how you might be able to use it to help you with macrolides in the United States but we have we can't really use this mycin to help with classification and we also want to be careful because midamycin is actually for cancer. Okay? Nitazole or nidazole depending on how you pronounce it this is an antiprotozoal and we see metronidazole quite often and I'll talk about how this stem gets a little bit messed up with that azul uh functional group oxacin so antibacterials and I mentioned the fluoroquinolone before so this is the quinolone derivative and oxacin is the actual stem that the World Health Organization has come up with but we really only see fluoroquinolones these days so the floxacin tends to be what most use to say okay well this is a fluoroquinolone antibiotic all right uh just five more here uh prim so it's a trimethoprim like and then trimethoprim is one that you use often with urinary tract infections very simple urinary tract infections or in combination with number 12 you know it's alpha methoxazole as that smz TMP the rifa antibiotic which is erythromycin derivative, so in the US we call it rifampin but outside the US and on the World Health Organization essential medicines list you'll see rifampicin. So again, this prefix is pretty consistent and then rifibutin. I'll talk about that in a sec but this rifa rifa is a pretty consistent prefix. Rifabutin is what we substitute for rifampin when we're working with TB patients that have HIV and we are using a protease inhibitor. So we don't want to use rifampin in that case or a phampasin. 12 is sulfur, again another prefix that's pretty consistent: sulfamethoxazole and sulfadiazine. Sulfadiazine's for severe burns. Sulfamethoxazole usually in combination with trimethoprim, we'll see for UTIs. Number 13 is thromycin. I see this a couple times on those note cards. It's not actually on the stem list. The mycin is as part of that streptomycy strain but you can be pretty confident with azithromycin, clarithromycin and erythromycin that those three are macrolides in the United States. However, fedaxomycin is a macrolide and it doesn't end in t-h-r-o-m-y-c-i-n. So again, we want to be careful with this one, kind of put a little asterisk next to it. Number 14 is zolid, oxazolidanone antibacterials like linezolid and that's a solid one. Okay, so going on to the errors that you'll see, a lot of times you'll see these note cards saying that own means a steroid and they're thinking of prednisone or deltasone or prednisolone, testosterone. Okay, the stem in testosterone is s-t-e-r for steroid. Stem in prednisone is p r e d for a prednisone type steroid. You'll also see some of the note cards saying that own is for opioids like hydrocodone or oxycodone and you might even see and I didn't put this on here own is for a diuretic like spironolactone. Okay, so that own is completely unreliable. You can't use that because here you see it's at the end of ceftriaxone and it's a cephalosporin. That's not a stem that's going to really lead you astray. I mentioned earlier about the in from antihistamine but I've even seen someone say that on one of the note cards that it's CNS stimulants and what they were thinking of um was like dexedrine, one of the brand names for uh the ADHD medication and those types of things. So again, in actually is at the end of around 18 and 19% of all medications, completely unreliable for giving you a drug classification. The next one we want to watch out for is this l-i-n-e so line is not uh a stem but I've seen many many cards say that it's a tricyclic antidepressant. What they're referring to is amitriptyline and the whole of tryptaline is what makes a tricyclic antidepressant. And I think the reason that this happens so much is that we don't really see nortriptyline much anymore but if you were to have seen amitriptyline and nortriptyline next to each other then you say oh okay I see there's a much longer stem there t-r-i-p-t-y-l-i-n-e. Same thing with fluoroquinolone, they'll actually put the drug class with the own saying that that is a steroid or something like that. So again, another one to really watch out for and the next one you'll see all the time that azole is the ending for antifungals. I can give you many many examples where this is wrong so metronidazole is an antiprotozoal then you have something like a proton pump inhibitor like esomeprazole that ends in azole and the stem there is prezzle sorry and then you have drugs like aripiprazole which are antipsychotics and the stem is piprazole so azole a-z-o-l-e this is an organic chemistry stem it's unreliable for drug classification and you'll also see this and I put this In the next slide with sulfamethoxazole, the azole stem will lead you wrong as well. Okay, so what I want you to take away from this is that you can use prefixes and suffixes if you get them from the proper source.

The United States Adopted Names Council list, the World Health Organization list, those are the ones that I used for memorizing pharmacology and that's really what you want to use. If you're going to use those note cards, I know it takes a lot of time to make your own but that's ideal. If not, at least take the time to look at these 14, make sure that the cards that you're using don't have these errors.

Thanks for listening to the Memorizing Pharmacology podcast. You can find episodes, cheat sheets, and more at memorizingfarm.com. Again, you can sign up for the email list at memorizingfarm.com to get your free suffixes cheat sheet or find our mobile-friendly self-paced online pharmacology review course at residency.teachable.com forward slash P forward slash mobile. Thanks again for listening.

Like to learn more?

Find my book here: https://geni.us/iA22iZ

or here: https://www.audible.com/pd/B01FSR7HLE/?source_code=AUDFPWS0223189MWT-BK-ACX0-059486&ref=acx_bty_BK_ACX0_059486_rh_us

and subscribe to my YouTube Channel TonyPharmD here: https://www.youtube.com/c/tonypharmd

Here is the Link to my Pharmacy Residency Courses: residency.teachable.com