Hospital Rotation Week 2: Process in Selecting Antibiotics

After years of pharmacy school, I am still overwhelmed by antimicrobials. I hope I am not alone in this feeling. All the “-micins”, “-mycin” “-cycline”, and “-cillin” begins to cluster up; and the binary, latin-root bacterial nomenclatures does not help.  I must admit, there are no easy ways to master antimicrobials, but it makes the whole learning process so much easier if you take a step back and try to see the BIGGER picture. These includes the general rules and principles that can be applied to the use of antibiotics almost universally. I say almost because there are always exceptions. Reviewing the different classes of antimicrobials, grouping them, and rationalizing the mechanism of action within each class helped me tremendously. I put together the following cheat sheets with the above mentioned process mind.

classification of antibiotics by MOA, chemical class, along with indications and toxicity
classification of antibiotics by MOA, chemical class, along with indications and toxicity
classification of antibiotics cont'
classification of antibiotics cont’

I consider understanding and memorizing antimicrobials’ spectrum of coverage to be one the most challenging obstacles to overcome in our field of study. A large amounts of antimicrobial misuse are due to prescribing antibiotics with either insufficient coverage or over-coverage. The effects in either cases can be detrimental to patients’ well-being.

Comprehensive list of selected microorganisms and antibiotic spectrum of coveerage
Comprehensive list of selected microorganisms and antibiotic spectrum of coveerage

The comprehensive chart above is meant to aid in your confidence building when asked to match the microbial to their respectively “kryptonite”, or so to speak. The key here is not just to memorize them but try to understand the behind-the-scene logic when making a selection. For example, rationalizing why cell wall synthesis inhibitors—the cephalosporin, penicillin, vancomycin, and carbapenems— could be poor choices for treatment of atypical bacterial infections. It makes sense because atypical species lack peptidoglycan cell wall layers; and subsequently, will not work. Perhaps, a macrolide and/or a fluoroquinlone would be better suited for this situation.

Conceptual understanding is essential, but somethings are required to be engraved into your memory. And we all know that no one makes it through pharmacy school without using silly mnemonics to memorize materials minutes before exams. Nobody! LD & NP are my two close friends, whom are also walking mnemonic generators. I am extremely grateful for their gift of coming up with silly, sometimes naughty, and most of all, memorable mnemonics. Guys, here’s a word of advice. When in doubt, pick gals to be your study buddies, they have a knack for these type of things. The mnemonics I mention and general rules of application I mention in this blog are ones I have learned through the years from friends and other resources—I claim no ownership for them. I am typing these as they come into my head and are in no particular order—I apologize for any inconvenience this may cause.

If you see a generic with the prefix of –cef or –kef, it’s a safe bet to say it’s of the cephalosporine class

Coverage wise, cephalosporine they are LAME because they are ineffective in:

  • Listeria
  • Atypicals species (mycoplasma, chlamydia, legionella)
  • MRSA (except for some 5th generations)
  • Enteroccus sp.

Generally speaking, cephalosporin coverage can be summarized by generations

  • 1st generation mainly have gram positive coverage
  • 2nd gen covers gram positive plus a few gram negatives (PEK)
  • 3rd and 4th generation expands their coverage to more gram negatives and more importantly, some Pusedomonas (HENPEK)
  • 5th generation tops it off with additional MRSA coverage.

Cephalosporin exceptions (cefoperzone—the oddball)

  • 3rd generation all have cross the BBB (blood brain barrier), except cefoperzone
  • All really cleared, except cefoperzone
cephalosporine agents classified by generations, indications, and toxicities
cephalosporine agents classified by generations, indications, and toxicities

Which antibiotics to recommend sun avoidance and the use of sunscreen? Think of Quit Sun Tan

Quinolones, Sulfonamides, Tetracyclines

Tetracycline covers: VACUum THe BedRoom

  • Vibrio
  • Acne
  • Chylamidia
  • Urea Ulyticum
  • Mycoplasma
  • Tuleremia
  • H. Pylori
  • B. budgoferi
  • Ricketsia

What drugs to avoid in sulfa allergy patients (call have S)

  • Bactrim SS/DS
  • Sulfasalazine
  • Dapsone (used to treat leprosy, dermatitis, and PCP prophylaxis in HIV patients)

When it comes to gonococcal and meningoccoal treatment, your DOC will be ceftriaxone.

Fluorquinolones can be used for gonococcal prophylaxis in patients with high risks

Rifampin can be used for meningitis prophylaxis in patients with high risks (ie. HIV, immunocompromised, chemotherapy patients)

There are many more, but I am running out of time today, I will mention more in future blogs. The R-rated mnemonics are still yet to come!

**source of featured image:


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