For my UME micro course, I made a figure that captures this terminology and lets learners compare/contrast spectra of activity visually. Let’s start with a horizontal bar that represents the spectrum of clinically important bacteria. We will represent antibiotics above that spectrum with another horizontal bar. If you shined a light from above the antibiotic, it would cast a shadow on that part of the spectrum – you might say it ‘covers’ that part of the spectrum. Narrow spectrum antibiotics cover only a sliver of the spectrum. We ‘expand’ or ‘broaden’ this coverage by selecting a ‘broad spectrum’ antibiotic. I’ve drawn the broad spectrum abx above the narrow spectrum abx to illustrate the concept of “escalation” and “de-escalation”. Let’s add names to the spectrum. On the left is Gram pos and on the right is Gram neg. I’ve also dropped 2 vertical lines – Abx A covers ONLY Gram pos, Abx C covers ONLY Gram neg, and Abx B covers a bit of both. Ideally, we could arrange all the clinically important organisms in a way that allowed us to depict every abx as a continuous horizontal bar – alas, this is not possible, and thus most abx have “holes” in their coverage! Let’s take it a step further and put actual organism names on the spectrum – this lets us compare/contrast important drug classes with granularity. For example, here’s the Gram pos part of the spectrum filled in with the penicillins and cephalosporins. Here’s the Gram neg end of the spectrum comparing some common beta lactam drugs. We can combine these two ends into 1 continuous spectrum. I also add anaerobes as the bridge between the two, and place intracellular organisms (like Legionella and Mycoplasma) on one end. In the next tweet will be the composite figure with all the commonly encountered abx! In this final figure, abx are divided by beta lactam and non beta lactam. Since we know that in vitro activity does not equal clinical use, I’ve color coded the abx bars – green means active and preferred, dark blue means active, and light blue means unreliably active. Dr. Varun Phadke @VarunPhadke2 #antibiotics #coverage #antibiogram #pharmacology #management #spectrum #table #sensitivities
