Inhaler rocket science

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Most of the common asthma medications (albuterol, Flovent, ...) are packaged in aerosol inhalers for delivery right to the lungs. Like any other aerosol, there's a medication suspended in a compressed gas propellant. As one of the last steps in the great CFC phaseout, these inhalers are being reformulated with hydrofluoroalkanes (HFA).1 In general, this is a pretty transparent process for consumers (except for the patent extensions being granted to the manufacturers for the propellant transition) but GSK actually decided to add some value here.

Asthma inhalers are what's called a metered dose inhaler, which is designed to emit a constant amount of medication per puff. Each inhaler is rated for a certain number of doses, but it can be pretty hard to determine when you've used up the rated capacity of the inhaler, especially since there's still propellant and drug in the inhaler afterward. Unfortunately, once you've used up the rated capacity you start to get inconsistent doses with each press and unlike aerosol deodorant it's kind of important to get the right amount of drug and it's not just a simple matter of holding the button down longer.

In what is no doubt the result of decades of research, GSK added one of those gizmos that conductors use to count the number of people on the train to their new Ventolin HFA inhaler, letting you know how many doses you have left. Pretty snazzy, huh?

1. So, what's the total amount of CFC emitted? Your typical inhaler is about 15 grams, so if you go through one inhaler a month, which is pretty typical for a moderate asthmatic, you're looking at 200g of CFC/person-year. Asthma incidence in the industrialized world is aroung 5%, so assume we're looking at something around 108 inhaler users, or about 20 million kg (20 kilotons) of CFC emitted. For comparison, the 2000 emissions of CFC-11 (the propellant used in albuterol) were order 75 kt. So, we're looking at a significant fraction of current emissions.


Most of the world's asmatics aren't being treated. Probably need to reduce your CFC emission estimate by about a factor of 500/6000 (the ratio of populations of US+Canada+Western Europe divided by global population). Obviously there's some untreated folks in US+CA+EU, and some treated folks outside those areas, but I wouldn't be surprised if the undercount and overcount there were roughly similar.

Craig: it looks like Eric only used 2B as the rough base population (10^8/.05). Given that there are over 1B people in the US/Canada/Europe/Australia/New Zealand, this looks right as rough single significant digit calculation.

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