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31 Aug

What’s going (on) down the drain? – More than you think!


31 August 2021

Julian Cox, Chair of CFNZ Otago Branch, shares the findings from a collaborative project between the branch and Otago University on nebuliser residue and antibiotic resistance.

View the Study Infographic >

The growing issue of antibiotic resistance

People with cystic fibrosis use antibiotics inhaled through a nebuliser to prevent and treat bacterial lung infections. In New Zealand, nebulised tobramycin is recommended for treating or managing infection with Pseudomonas aeruginosa, a major cause of lung infection with people with CF.

Bacteria are very good at adapting to their environment and changing in ways that decrease or eliminate the effectiveness of antibiotics. This antibiotic resistance is a serious and growing health problem.

Knowing that Pseudomonas particularly like living in moist environments (lungs and drains) I’ve always been a little concerned about what might be happening down our sink drain when we clean up the nebuliser that has just been used for tobramycin. Are all the little P.a’s there becoming antibiotic resistant?

There also seemed to be a disconnect between manufacturing advice for cleaning nebulisers (e.g. “rinse and clean to remove residue after use”) and national advice for disposing of antibiotics (e.g. “never pour down drains or put in household rubbish”).

Curiously, while I’m pretty adept at internet research, I couldn’t seem to find any information on this. It turns out that’s because, if anyone has thought about it, they haven’t formally studied it.

I happened to see an advert in the paper for the Otago Participatory Science Platform, which provides funding to promote citizen science.  A few emails and phone calls later (it really was that easy) and CFNZ Otago Branch had almost $20,000 in funding and the University of Otago fully on board to investigate.

The research was led by Karyn Maclennan of the Department of Preventive and Social Medicine with Greg Walker and his research technician, Pummy Krittaphol, of the Pharmacy department responsible for most of the science.

Surveys, spectrometers, and samples

The first task was to confirm that, despite national guidelines not to wash antibiotics down the drain, it wasn’t just the Cox household rinsing their neb into the sink. So we set up a phone and online survey which did indeed confirm everyone on inhaled antibiotics who took part in the survey is doing just that.

Next job was to find out just how much tobramycin was going down the drain from a typical neb wash. This is pretty tricky given that tobramycin dissolves in water and you don’t know exactly how much is going into and coming out of the lungs.  Luckily the Pharmacy department has a very expensive machine call a Liquid Chromatography Mass Spectrometer (LC-MS).  Given some pure tobramycin they can develop a test which can then be used to work out how much tobramycin is in the water.

Next, we needed to collect some rinse samples from actual people on inhaled tobramycin.  They were given some distilled water and used that to wash the neb into a special bowl from which a sample of the rinse water was taken. Using the LC-MS we could work out the concentration of tobramycin in the water.

Down the drain

When the results came in, I think everyone was a little taken aback - 40% of the contents of that little tube of tobramycin ends up being washed down the sink. That’s a lot!

If you’re wondering where all that residue is coming from – much of what you inhale gets exhaled out again and then condenses back on the neb (especially if you are using a filter), plus there is always some left over in the nebuliser reservoir that doesn’t get aerosolised.

You may also be thinking – woah does that mean I’m not inhaling the right amount of tobramycin?  Fortunately, no, it does not.  Efficacy studies looking at the appropriate dose of nebulised tobramycin for people with CF account for the dose that actually gets into the lungs.

Survey results

Unfortunately, we still don’t know for sure if the amount of tobramycin going down the drain might be causing antibiotic resistance. To work that out we’d need to develop some more cunning tests on the microbes themselves.

However, we did rope in some experts as part of a community Hui on the results.  Iain Lamont of the Otago University Pseudomonas lab thought that, while many Pseudomonas microbes present may well be killed at that concentration, it was also possible that the exposure could lead to some tobramycin-resistant Pseudomonas.

Safely washing nebs going forward

The study has raised a number of questions that require further investigation. It may be possible to construct a low-cost household filter system which extracts the antibiotic from the rinse water, for example.

In the meantime, disposal of the rinse water down the toilet (with the lid closed) was one key recommendation from this review that no one from our survey was doing. We also recommend weekly bleaching of the key drains. Bleach works through a different mechanism to antibiotics and is likely to be effective on antibiotic resistant Pseudomonas.

Thanks to the researchers, participants and supports of the study. It’s been really affirming to see a small question that I had pique the curiosity of others as well.  I was particularly pleased to hear that Iain and Greg have now received significant funding for further research (based partly on the LC-MS test Greg developed for this study) that could lead to more effective treatments of Pseudomonas.

It’s important to follow best practice guidelines, such as those in the 2020 Bell et al review: Nebuliser hygiene in cystic fibrosis: evidence-based recommendations. 

  1. Wash nebuliser components in warm water and dish washing liquid in a dedicated plastic, glass or metal bowl.

  2. Dispose of nebuliser wash water down the toilet, closing the lid before flushing.

  3. Clean toilets and drains with bleach – this may help kill any Pseudomonas bacteria that are present.