Today we’re going to talk about antibiotics and review the primary antibiotics we use in clinical medicine, along with some of the warnings that go with them. Please remember guys, if you don’t document risk factors, that will come back to bite you. You always want to know about rashes. If your patient gets a rash, they need to stop their antibiotic and call you, because of Steven-Johnson syndrome and erythema multiforme. We want to talk to patients about diarrhea because all antibiotics can cause C. Diff. If you have a female on birth control pills, you want to warn her that she needs to use barrier protection while on antibiotics.
We’re going to talk about clindamycin first. Clindamycin kills anaerobes and gram-positive cocci. It has an anti-toxin effect, which makes it good for toxic shock syndrome and necrotizing fasciitis. Clindamycin can be used for skin infections, including MRSA. It’s often used in dental work because there are anaerobes living in the mouth. It is linked to the highest rates of C. Diff. infection, which is why I stay away from clindamycin. Even though it’s probably lower than 10%, I don’t like to take the risk.
Vancomycin is for gram-positive and it’s your gold standard for MRSA infections. It only treats gram-positive infections so you need to be aware of that. It’s not as effective as antibiotics like nafcillin for methicillin-sensitive Staph aureus (MSSA). The oral form of vancomycin is not well-absorbed, so when we use it for MRSA, we always use IV. The fact that it’s not well-absorbed through the gastrointestinal tract makes it awesome for C. Diff. infections and it’s found to be superior to metronidazole.
Gentamycin is the opposite of vancomycin because gentamycin is only for gram-negatives. It’s fallen out of favor due to its ototoxicity and nephrotoxicity, but it’s a really good antibiotic for gram-negative substances including pseudomonas. It used to be thought that the nephrotoxicity was caused by the peaks and troughs of the gentamycin. Now we know it’s based on duration therapy so we try to put patients on gentamycin for just a short number of days.
Metronidazole, or Flagyl, covers anaerobes to include C. Diff. and some protozoans. It can be used for C. Diff. infections, but it’s considered a second-line agent nowadays. Remember that we advise patients on metronidazole to not drink alcohol, as they could have an Antabuse-like reaction. Metronidazole is wonderful for trichomonas, so I teach, “If it’s flagellated, use Flagyl,” meaning that trichomonas is flagellated.
Nitrofurantoin, or Macrodantin, is a really good antibiotic for most gram-positives and most gram-negatives. It’s awesome for urinary tract infections. It’s considered the antibiotic of choice for first- or second-trimester pregnant females, even though Keflex is often used. Nitrofurantoin does not perfuse the kidneys well, so don’t use it for kidney infections.
Doxycycline is a pretty good antibiotic. It’s reasonable for community-acquired pneumonia. It’s great for chlamydia. It’s good for skin infections when you’re considering MRSA. It’s the drug of choice for early Lyme disease. The problem with doxycycline is calcium. It can affect calcium in the bones and teeth of kids under 8, so we avoid it. It’s photophobic, so we advise our patients to stay out of the sun. It can cause some dysphasia, real difficulty swallowing. The way I teach it at my live conferences is: doxycycline is used as a pleurodesis agent, so it causes some inflammation to membranes and therefore would cause some inflammation to the gastrointestinal tract when swallowing.
Trimethoprim / Sulfamethoxazole
Trimethoprim/sulfamethoxazole (Bactrim) are sulfonamides and the drug of choice for the Pneumocystis jiroveci pneumonia seen in HIV-positive patients. It’s reasonable for UTIs, salmonella infections, acute bronchitis and otitis media, and it’s good for skin infections.
Don’t ever, ever, ever use Bactrim with coumadin or warfarin, as it will raise the INR to nine in approximately two doses. They say Bactrim is about 10-20% resistant to E. coli and in UTIs, but please understand that’s a laboratory phenomenon. Just because the lab says the bacteria is resistant to an antibiotic, it doesn’t mean that the clinical response is the same. If you are working and get the report back that someone was placed on Bactrim with bacteria supposedly resistant to Bactrim, just call the patient and make sure they’re having clinical improvement. If so, you don’t need to change the antibiotic.
Penicillin really only kills strep and syphilis, so any time you’re using penicillin, you’re really treating a strep throat. Syphilis is making a comeback, so you’d be using it for syphilis. Second-generation penicillin is our anti-staphylococcal penicillin. That’s methicillin, nafcillin and oxacillin. Penicillin is reasonably good for staph and strep; therefore, it covers cellulitis and otitis media. It’s been used for endocarditis and bacteremia, but it does not cover MRSA so the class has fallen out of clinical utility.
The aminopenicillins, ampicillin and amoxicillin, cover gram-positives, no staph, and some gram-negatives. “SMH,” in a text, means “shaking my head.” I’d like you to take three fingers and put them on your throat. Now, SMH stands for Strep pneumoniae, Moraxella catarrhalis and Haemophilus influenzae. Those three germs love to colonize in the upper airway, which makes them players in otitis media, sinusitis and even community-acquired pneumonia. Amoxicillin treats them really well. We never use amoxicillin in the lungs because atypicals can affect the lungs and amoxicillin will not treat those.
Piperacillin / Tazobactam
The super-heavyweight antibiotic that you should be aware of is piperacillin/tazobactam, or Zosyn. It’s really powerful for gram-positives and gram-negatives. We will use it for healthcare-acquired pneumonia with vancomycin. If I have a really bad intraabdominal infection, I would use Zosyn as well.
I recommend you really know the most common first generations and the third generations of cephalosporins. The first generations are cefazolin and cephalexin. They’re good for mild to moderate non-purulent cellulitis if MRSA is not suspected. They’re also pretty effective for UTIs in pregnant women.
Ceftriaxone, or Rocephin, is a fantastic antibiotic. It’s really good for gram-positives and gram-negatives, so we use it for community-acquired pneumonia in combination with azithromycin. It’s used for meningitis, where the dose is 2 grams of ceftriaxone with 1 gram of vancomycin. In the treatment of gonorrhea, we give it as a 250mg milligram IM shot. We use azithromycin as well to treat chlamydia at the same time.
Macrolides cover atypical organisms, such as chlamydia, mycoplasma and legionella. Erythromycin was the first-generation macrolide and therefore, it covers gram-negatives poorly. Overall, the macrolides cover most gram-positives and gram-negatives.
Fluoroquinolones are an antibiotics you need to be mindful of. There are a lot of side effects of ciprofloxacin, moxifloxacin and levofloxacin. These antibiotics are pretty effective for all germs. They cover gram-positives, gram-negatives, atypicals, anaerobes and Pseudomonas. The only exception is ciprofloxacin, which does not cover gram-positives, but is really good for gram-negatives.
We don’t use it in kids less than 18; we don’t ever use it in pregnant females. When you look at the side effects, you’ll see QT prolongation, tendon rupture, an increase in liver functions, teratogenic effects, cartilage damage and dysglycemia. In July 2018, the FDA noted 67 cases of life-threatening hypoglycemia with 13 deaths and nine permanent disabilities so we need to be a lot more careful using fluoroquinolones.
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