Intravenous antibiotics and C. diff

Pet

I noticed that a lot of intravenous antibiotics come with a C.Diff risk in the guidelines. Similarly, the treatment, in many cases, is IV metronidazole.

How does this work? If you're injecting an antibiotic, how does it affect the gut flora enough to cause C.Diff/kill C.Diff? Surely only oral antibiotics would work in the GI tract? Unless you can achieve high enough plasma concentrations that the epithelial cells contain enough to achieve bactericidal levels, but surely it's far more efficient PO?

note: idle wonderings/college research, not medical advice.

flerb22

oral vanc can be used, so i guess its a little from column A a little from column B in regards to what you said.

Pet

Yeah I know oral can be used and works, I'm just wondering why bother with IV at all, and if/how well it works.

Ihaveanopinion

There's a lot of work being done at the moment on Pro-biotics and their use in C.diff. The idea being that you give extra 'good bacteria' so that if your natural flora is reduced by antiobiotics - you can replace or augment them with yoghurt etc.

A lot of that kind of work is being done in UCC at the moment

SomeDose

Pet wrote: »

I noticed that a lot of intravenous antibiotics come with a C.Diff risk in the guidelines. Similarly, the treatment, in many cases, is IV metronidazole.

How does this work? If you're injecting an antibiotic, how does it affect the gut flora enough to cause C.Diff/kill C.Diff? Surely only oral antibiotics would work in the GI tract? Unless you can achieve high enough plasma concentrations that the epithelial cells contain enough to achieve bactericidal levels, but surely it's far more efficient PO?

note: idle wonderings/college research, not medical advice.

Metronidazole in c.diff is almost always oral (not IV, see below). In terms of the risks of causing the disease, it's all to do with the pharmacokinetics of the various IV antibiotics and how well they're distributed in body tissues. Antibiotics such as cephalosporins, ciprofloxacin and clindamycin will, after parenteral administration, distribute widely throughout the body. This means a certain concentration of the drug will be present in the gut & bowel tissue. These are broad spectrum antibiotics which will deplete the normal protective gut flora and allow c.diff to colonise.

In terms of treatment, IV therapy is essentially made defunct for the same reasons outlined above. Oral vancomycin is active against c.diff yet IV vancomycin is useless. Why? Because when given IV it doesn't distribute into the gut, and hence why IV vanc treatment doesn't put someone at risk of developing c.diff. The other drug to treat the disease (metronidazole) has such good absorption when given orally (basically 100%, same as IV) that there is no need to give it IV. In life-threatening disease the IV route may be used purely because higher peak plasma levels will be achieved in a shorter time frame.

charlieroot

Some antibiotics "select out" C. diff, ie they kill off other bacteria, C. diff is resistant to the antibiotic and so can proliferate unopposed. Treat with oral Vancomycin - oral vanc is not absorbed but will work in the GIT. However I believe metronidazole is the first line treatment for C. diff pseudomembranous colitis with Vanc being second line. Metronidazole is effective against protozoans and anaerobes (Clostridia are anaerobes). My micro lecturer would be so proud - I actually remembered something

As an aside - Clostridia spores are resistant to the alcohol gels used in hospitals - hence why its also important to wash your hands with soap and water!