Is there supposed to be any logic to this or is it just memorization? I don't see anything except memorizing, but want to make sure I'm not missing something before I punish myself too much trying to learn it
Gracias!
This will be very general, and someone else can come along and elaborate further or correct me, but it basically boils down to gram positive vs. gram-negative; aerobe vs. anaerobe. Sensitivities change your choices.
Penicillins work okay for sensitive gram-positives (Staph and Strep) and especially
syphilis. Nafcillin for MSSA; vancomycin for MRSA. Aminopenicillins (like amoxicillin) have broader gram-negative coverage.
As a general rule, the higher the generation of cephalosporins, the greater gram-negative coverage you have. Many Enterococcus species are intrinsically resistant to cephalosporins; use ampicillin instead unless sensitivities indicate otherwise. First-generation is good for cellulitis caused by Strep. Third-generations are good for being able to cross the BB barrier (N meningitidis). The only cephalosporins that work against Pseudomonas are fourth-generation.
Fluoroquinolones tend to work well against organisms that cause respiratory and advanced urinary tract infections. Some Pseudomonas strains are susceptible to ciprofloxacin.
Tetracyclines are good against many bugs; usually they're first line against rickettsial diseases and chlamydia. They are also effective against spirochetes.
Macrolides are good in combination with higher-generation cephalosporins for common organisms causing community acquired pneumonia; alone (specifically azithromycin) they are good for chlamydia and organisms that cause URI. They also work against organisms causing atypical pneumonia.
As a
general rule, clindamycin is good against anaerobic infections above the diaphragm, and metronidazole below the diaphragm. Metronidazole is also good against trichomonas and C diff. Depending on the severity of the C diff infection, oral vancomycin may be needed as well.
Piperacillin/tazobactam has very broad coverage; commonly used if Pseudomonas is suspected, and also covers anaerobes.
Carbapenems, linezolid, and other "big-gun" antibiotics should only be used in the event of serious resistant infections.
Aminoglycosides are generally used in conjunction with other antibiotics, especially in the treatment of infective endocarditis (gentamicin). Also commonly seen is inhaled tobramycin used in CF patients with Pseudomonas colonization.
Sorry if you were looking for more specific information, but your question really covers a broad topic and this is about as general as it gets (unfortunately). As it is, I feel like I left something important out. If you have specific questions, feel free to post them and I'll try to answer to the best of my knowledge.
