Introduction
Salbutamol sulphate metered inhalers are frequently observed to be able to discharge (puff) many times after the listed actuations on the product.
This leads to confusion in patients and clinicians as to whether the device is delivering therapeutic doses of Salbutamol or just the gas propellant. This paper reviews two common brands of salbutamol metered aerosol products to document how many total activations are possible from new.
Context
People experiencing asthma are at risk of acute exacerbations known as flare-ups (previously "Asthma Attacks")(National Asthma Council Australia, 2015). The pathophysiology involved frequently includes an immunoglobulin E mediated immune response to an allergen, like smoke, dust mite, foods and fragrances. Alternatively exercise, stress and ambient temperature/humidity fluctuations may lead to a flare up (Kim and Mazza, 2011).
Regardless of aetiology, the disease is characterised by cough, bronchiectasis, bronchospasm, and bronchiole luminal narrowing from oedema. This triad significantly causes increased work of breathing manifesting subjectively as 'shortness of breath' and chest tightness, and objectively as dyspnoea, accessory muscle use, cough and wheeze (Holgate, 2008).
A short acting beta-2 receptor agonist (SABA) delivered as a metered aerosol (MA or "puffer"), nebuliser is common initial treatment (Asthma Foundation, 2015;Australian Resuscitation Council, 2010). In most countries the medication of choice is Salbutamol (North America - Albuterol) often referred as "blue reliever medication".
It is an observation by many clinicians in emergency practice, that patients using their SABA, are unaware of the correct use, correct dose and remaining drug in their MA. Irrespective of the brand of Salbutamol, the metered aerosol delivers 100micrograms, and reports 200 doses. Despite this, a common observation is that long after 200 actuations, the device is capable of being discharged many more times.
This may cause concerns with those individuals that, during a flare-up, diligently self administer their SABA, believing it to be discharging drug, when it may be void of anything but propellant gas.
Some other metered aerosol products include a counter device that informs the user of doses used, or doses left. Salbutamol MA products available in Australia don't have this feature, so the user is required to keep a tally. There is no way of knowing if the MA is drug depleted.
Question
Despite advertising 200 metered doses, how many times will a salbutamol MA discharge before it stops actuating?
Methodology
A simple experiment was designed where six (6) metered aerosols (three of two different brands) of salbutamol were discharged to extinction.
To minimise expiry dates, ambient temperature, atmospheric pressure or humidity being a corrupting variable, all discharges of the medication were performed on new stock, on the same day, same time, and at the same location.
Data
Ambient temperature was recorded at 23 degrees Celsius. Altitude was sea level .
The brands of salbutamol sulphate included were Ventolin (GlaxcoSmithKline) expiring 4/2017 and Asmol (Alphapharm) expiring 2/2017.
The experiment was conducted at the end of September 2015 so all medication had a minimum of 16 months prior to its expiry date.
Medication was discharged to exhaustion of propellant. One discharge per second in blasts of 10 puffs (barrages), followed by 4 shakes of the device between each barrage.
Asmol 1- totalled 276 discharges
Asmol 2- totalled 275 discharges
Asmol 3- totalled 273 discharges
Ventolin 1- totalled 272 discharges
Ventolin 2- totalled 274 discharges
Ventolin 3- totalled 274 discharges.
Results
From this small experiment it is apparent that the two brands were similar in the total number of unit discharges. Range of variance 272-276
Mean 274, mode 274, median 274.
It is fair to report that salbutamol sulphate metered aerosols deliver 274 +/- 2 actuations.
Discussion
Whilst it is clear that the MA devices assessed in this experiment discharge their advertised actuations, it is concerning that at a mean discharge rate of 272, this represents 72 puffs more than the reported doses. Given this premise it was outside the scope of this study to assess the content of each discharge.
It is not known if after 200 actuations the remaining 72 puffs contain drug or just propellant gas. A common observation in emergency departments is that a patient reports that their "puffer" is not "working" despite the apparent discharging. This could be poor technique, out of date medication or indeed use of a MA that is drug depleted yet continues to discharge gas. If the later is true, this represents a patient teaching opportunity, and nurses/doctors and pharmacists in a position to offer patient teaching should be informing their clients of the need to tally their MA use.
Limitations
The study was limited by a small sample of MA devices (n=6) and only two brands of salbutamol were included. A more statistically powerful experiment could be conducted to assess a larger number of units, and include a larger number of brands.
A second limitation is that despite advertising only 200 doses on the labelling, this study did not analyse the content of each spray, so can not surmise that all sprays were delivering a full 100micrograms of salbutamol, or only the first 200 actuations. A robust content analysis of the full 272 (+/- 2) sprays would allow conclusions to be made as to whether manufacturers over compensate and include more than 200 metered doses, or whether, as advertised, each device only delivers 200 doses, and any excess is merely propellant.
Conclusion
Six metered aerosols of salbutamol sulphate were discharged to exhaustion to assess quantity of actuations. All devices (n=6) discharged between 30-36% (272 +/- 2) more times than advertised. It is not knows if the mean 72 extra actuations contain any drug, or just propellant.
Author concludes more research and content analysis is needed, and a practice application reinforces the ongoing need for clinicians to provide education to their clients to keep tally on their salbutamol use.
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Refs
National Asthma Council of Australia
http://www.nationalasthma.org.au/handbook
Asthma Australia
http://www.asthmaaustralia.org.au
Australian Resuscitation Council.
Www.resus.org.au
HOLGATE, S. T. (2008), Pathogenesis of Asthma. Clinical & Experimental Allergy, 38: 872–897. doi:10.1111/j.1365-2222.2008.02971.x
Kim, H and Mazza, J. (2011), Asthma. Allergy, Asthma & Clinical Immunology, 7(Suppl 1):S2.
