antibiotic spectrums of activity”? This is a difficult task as there are so many. Personally I have never found lists of medical information that helpful, I would much rather come up with a mnemonic. However, I’m stumped for a mnemonic to remember antibiotic spectrum of activity, so a list it must be. What I have done though is reduce a very long list into six short related lists, which I hope are easier to remember.
Remembering the 6 lists below will help to ensure patients are on an antibiotic that is active against their infection.
- Active against Gram-positive and Gram-negative bacteria (Broad-spectrum antibiotics)
- Active against anaerobes
- Active against Pseudomonas spp.
- Active ONLY against Gram-positive bacteria
- Active ONLY against Gram-negative bacteria
- Active against “non-culturable” bacteria
Lists 1 and 2
Example B: In patients with serious penicillin allergies Beta-lactams including Co-amoxiclav, Piptazobactam, Ertapenem, Imipenem or Meropenem are contraindicated. Combinations of antibiotics are therefore needed to cover the gut flora, such as Teicoplanin OR Vancomycin (which only have Gram-positive activity) PLUS Metronidazole (which only covers anaerobes) PLUS either Ciprofloxacin OR Gentamicin (both of which have excellent Gran-negative activity).
Why a combination of antimicrobials? Combination antimicrobials are used to try and prevent further development of resistance (Pseudomonas aeruginosa is notorious for acquiring new resistance mechanisms), in non-CF patients two antimicrobials are usually enough. It is unlikely that bacteria will become resistant to two or more antimicrobials at the same time therefore resistance is less likely to occur. Even if the bacteria do become resistant to
one of the antimicrobials the other agent(s) will be able to kill the bacteria.
List 4 and 5
pneumoniae (a non-culturable bacterium). What antibiotic should they be treated with? Erythromycin, Clarithromycin, Azithromycin, Ciprofloxacin, Levofloxacin and Doxycycline all could be used to treat this patient.
If you can learn these six lists it starts to become much easier to understand why certain antibiotics are chosen to treat certain infections. It also enables you to choose alternatives when patients are allergic to first line antibiotics found in guidelines. Download a handy postcard of the 6 lists and keep it in your book Microbiology Nuts and Bolts.
Give it a try and see if it helps. Pass it on too. If you can think of any easy way of remembering them then let me know, I’m always keen to know how others have learned their microbiology.