Managing infections
About
a third of patients in hospital will be given an antibiotic, and so it is
important that you know how common infections are treated. Specifically, you
need to know how different organisms are classified, which bacteria are most likely
to infect different parts of the body, and which antibiotics are effective.
Organising bacteria
There are several different ways to broadly
classify bacteria. In a clinical setting they are grouped as Gram positive, Gram negative and atypical according to the
structure of their cell walls or where they live. They are also distinguished according to their
oxygen requirements as anaerobes or aerobes. Look at the table below and
write down an example of each that you have encountered in practice, then click to check your answers.
| Gram positive | Click to reveal
Staphylococci
Streptococci Enterococci Listeria Bacillus |
| Gram negative | Click to reveal
E.coli
Enterobacter Haemophilus Helicobacter Klebsiella Proteus Pseudomonas Salmonella Shigella |
| Anaerobic | Click to reveal
Clostridia – also mostly Gram positive
Bacteroides - also Gram negative |
| Atypical | Click to reveal
Mycoplasma
Chlamydia Legionella – also Gram negative |
There are some exceptions such as Mycobacterium tuberculosis which is Gram positive but it doesn’t take up a Gram stain. This is because its cell wall contains lots of mycolic acid.
What bugs are where?
Remembering what
bacteria are likely to infect different body systems is important, especially
when making decisions about antibiotic therapy empirically (‘blind’) before laboratory
sensitivities are available. There is no easy way to remember this, but the
picture below illustrates in general what bacteria are found where.
What
is the most common infection you see on your ward? What is the causative
organism and what body system does it affect?
Bugs and drugs
As a pharmacist you need to
have a working knowledge of the spectrum of commonly used antibiotics. It is difficult to group drugs according to
their activity against different pathogens; some only cover Gram positive or
Gram negative organisms, but others may cover mostly Gram negative organisms but
have some Gram positive cover (e.g. ciprofloxacin, gentamicin), or vice versa
(e.g. rifampicin). Therefore the following table lists antibiotics according the
groups of pathogens against which they show most activity.
| Used only or mainly for Gram positive (Staphylococcus and/or Streptococcus) |
Click to reveal
Clindamycin
Flucloxacillin Fusidic acid Linezolid Phenoxymethylpenicillin and benzylpenicillin Rifampicin Teicoplanin Vancomycin |
| Used only or mainly for Gram negative | Click to reveal
Aztreonam
Ceftazidime Ciprofloxacin Colistin Gentamicin, tobramycin, amikacin |
| Anaerobic | Click to reveal
Clindamycin
Co-amoxiclav (infections above the diaphragm) Ertapenem, imipenem, meropenem Metronidazole Piperacillin-tazobactam |
| Atypicals | Click to reveal
Azithromycin, clarithromycin, erythromycin
Ciprofloxacin, levofloxacin, ofloxacin, moxifloxacin Doxycycline, minocycline, oxytetracycline |
| Broad-spectrum | Click to reveal
Amoxicillin, co-amoxiclav
Azithromycin, clarithromycin, erythromycin Ceftriaxone, cefotaxime, cefalexin Chloramphenicol Doxycycline, minocycline, oxytetracycline Ertapenem, imipenem, meropenem Levofloxacin, moxifloxacin Piperacillin-tazobactam, ticarcillin-clavulanic acid Trimethoprim, nitrofurantoin |
Again this is difficult to memorise – you may like to keep the table to hand, but don’t use it in isolation; ALWAYS check your local guidelines.
Broad versus narrow-spectrum antibiotics
Inappropriate use of broad-spectrum antibiotics is associated with the selection of resistant bacteria and the induction of Clostridioides difficile infection (CDI). Their use can also cause long-lasting harmful changes to the body’s protective microbial flora.Cephalosporins, ciprofloxacin, clindamycin and co-amoxiclav (‘the 4Cs’), and piperacillin-tazobactam and the carbapenems have been most strongly associated with CDI, but all antibiotics should be avoided unless there are clear clinical indications for their use.
Indications for using broad-spectrum agents include life-threatening infection (e.g. neutropenic sepsis), significant risk of a resistant pathogen (e.g. recent hospital admission, care home resident, recent exposure to antibiotics), or on advice from a microbiology doctor.
Antibiotics should always be used for the shortest duration possible that gives an appropriate clinical outcome.