It is common for learners to struggle with memorizing antibiotic coverage when they are first introduced to the subject. With so many unfamiliar bacteria and antibiotics to know, it can be more than enough to get your head spinning.
In school, you probably learned the spectrum of activity for antibiotics by grouping bacteria into 3 common classifications:
Gram-positive bacteria (e.g., Streptococcus, Staphylococcus, Enterococcus)
Gram-negative bacteria (e.g., E. coli, Klebsiella, Salmonella, Shigella, Pseudomonas)
Atypicals (e.g., Chlamydophilia, Legionella, Mycoplasma)
Additionally, you learned that they are then further subclassified into aerobes, anaerobes, lactose-fermenting, and non-lactose-fermenting. But wait, don’t get cross-eyed just yet! Memorizing the spectrum of activity of antibiotics does not have to be that difficult. In this article, I’ll share some memorization tips on remembering the common bugs and what drugs cover them.
BUGS AND DRUGS
A great tip for remembering antibiotic coverage starts with memorizing the antibiotics that cover the major categories of bacteria including anaerobes and atypicals as well as resistant pathogens such as methicillin-resistant staphylococcus aureus (MRSA) and pseudomonas. From there, you can build upon your knowledge of other less commonly seen bacteria or infections through the application of the material during class, rotations, and clinical practice.
Needless to say, these are a MUST for you to know for exams. Review the mnemonics below and quiz yourself to see how much you remember.
NOTE: Clindamycin, doxycycline, and Bactrim (generic: sulfamethoxazole/trimethoprim) cover community-acquired MRSA infections while vancomycin, ceftaroline, and daptomycin cover hospital-acquired MRSA infections. Other antibiotics not listed include: linezolid, telavancin, dalbavancin, oritavancin, tigecycline (this mnemonic story can get pretty long!)
NOTE: Atypical bacteria do not color with Gram staining (because they lack a cell wall) and remain colorless. They are neither gram-positive nor gram-negative; they are ATYPICAL! 🙂
NOTE: These are the main antibiotics that empirically cover anaerobes. There are other antibiotics that do have some anaerobic coverage but since anaerobes are hard to culture and identify, empiric therapy is often used in practice.
NOTE: Other antibiotics not listed include: cefiderocol, colistin, ceftolozane/tazobactam
TIPS FOR SUCCESS
- Keep in mind, memorizing these antibiotic spectra of activity can come in handy for exams but it doesn’t always apply to clinical practice (ex: you wouldn’t recommend daptomycin for MRSA pneumonia since daptomycin gets deactivated by the lung surfactants. You also wouldn’t recommend doxycycline as the first-line option for hospital-associated pneumonia.)
- Other things to keep in mind when recommending an antibiotic to the team: potential toxicities, renal and hepatic function, CPK monitoring (esp. with daptomycin), which type of infection the drugs can or cannot be used for (moxifloxacin should not be used for UTIs as it doesn’t concentrate well in the urine making it ineffective), contraindications, drug interactions, and routine antibiotic doses (pneumonia dosing vs. bacteremia dosing)
- At the end of the day, the best way to become comfortable with bugs and drugs is to practice, practice, practice. It takes time and effort but eventually, you’ll start to see a pattern with which antibiotic should be used based on patient-specific factors, cultures and sensitivity, and the type of infectious disease.
A) Which of the following antibiotics can be used for a patient with MRSA+ pneumonia?
B) All of the following antibiotics cover pseudomonas EXCEPT for?
C) A patient is in need of anaerobic coverage for a diabetic foot infection, which of the following antibiotics would provide adequate anaerobe coverage?
D) Which antibiotic would provide coverage for atypical pathogens and streptococcus pneumoniae in a healthy patient diagnosed with community-acquired pneumonia (assuming local resistance is low)?
ANSWERS: A. 2, B. 3., C. 3., D. 3.