How Much Medicine gets to the Lungs?

Hi everyone,

I'm at uni and have a housemate studying biology and they have to do short tests each week that add up to a certain percentage of their overall grade on the computer. These tests are in the format of multiple choice queations and they have articles for the students to read before answering the questions, the one my housemate did last week was about Asthma and we were talking about it and she said according to this article only about 10% of all inhaled medicine gets to the lungs and 50% goes to the stomach with the remaining 40% staying in the mouth and throat. I just found this really suprising as arent inhalers used to maximise the amount of medicine to the lungs? im not worried about this and my Asthma is very well behaved at the minute, but just curios really, can anyone shed any light on this one? do you guys think this is true? i wouldnt like to say myself, hence why im posting this lol

Claire x

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Hi Claire,

This is broadly true - I think most studies quote a figure of around 15 - 20% of the drug from inhalers going to the lungs, with the majority of the rest being deposited in the mouth and throat and eventually swallowed.

Obviously the recommended dose of inhaled steroid is adjusted to account for this, and inhalers are designed with the aim of optimising drug delivery to the lungs. Good inhaler technique and using a spacer also help to get as much medication as possible down to the lungs.

It's worth commenting that most of the commonly used inhaled steroids, when swallowed, undergo what is known as 'first pass metabolism' - which means that when absorbed from the gut, they go straight through the liver, and are removed from the blood almost entirely by the liver before they hit your main systemic (body-wide) circulation. These means that even if you swallow large quantities of these drugs, you shouldn't be at much risk of systemic steroid side effects, because they are still not really getting into your body as a whole.

Hope this reassures you a bit that what you have been told about inhalers is broadly true!

Take care

Em H