When a pharmacy substitutes a generic inhaler, the molecule is equivalent and the device usually is not. A patient competent with a metered-dose inhaler may be entirely unable to generate the inspiratory flow a dry powder device needs, and nobody will find out until the next exacerbation.
So treat every substitution as a new prescription. Ask the patient to bring the actual device to the next appointment — not the box, not a photograph — and watch them use it. Most errors are visible in one attempt: no exhalation first, no breath-hold, firing before inhaling, or an inspiratory effort too weak for the resistance.
Where a patient uses more than one inhaler, try to keep the device type consistent across them. Mixing a pressurised canister with a dry powder device doubles the technique the patient must remember, and the one they use less often is the one they will get wrong.
- Ask the patient to bring and demonstrate the device at every review, not describe it.
- Re-teach technique after any generic substitution or device change.
- Keep device types consistent across a patient's inhalers where the formulary allows.
- Add a spacer for any pressurised metered-dose inhaler in a patient with poor coordination.
- Record which device was dispensed, not just the drug, so the next prescriber knows what the patient is actually using.
Why it matters
Treatment failure attributed to disease progression is often a device the patient cannot use.
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