The answer to a question like this usually depends on your target regulatory system, so it would help if you could indicate this target..is it the EU, USA, etc?
Also, please note that ISO 13485 has a medical device definition but in practice you have to use the definition and regulastions of your target reg system because they have precendesce over 13485. In the case of possible drug-device combinations it´s even worse because theses interactions are not clear in some reg systems today.
I don't know of any clear way to determine the answer under the US FDA's rules other than either by precedent/predicate if you can determine the regulatory status of a similar existing product, or by getting an informal or formal judgment from FDA.
I also don't know of a clear way to get a judgment from FDA regarding combination-device status involving CDRH and CDER. My understanding from past inquiries regarding combination-device issues is that CDRH and CDER decide among themselves who will interact within each of the sub-organizations to make the decision, on a case by case basis. I don't interact with CDER often, though, so perhaps there's an obvious starting point there on this question that I don't know about.
When I worked for a rather large pharmaceutical company (in another life!), I was responsible for producing some of the documentation for the MDIs (metered dose inhalers), spacer and DPIs (dry powder inhalers). We separated the canister (seen as the drug/device combination) from the inhaler itself for the EU, the inhaler, spacers and DPI units being classed as a Class I medical devices (self certification for the MHRA in the UK where they were manufactured i.e. they were CE marked). However, all the supporting performance information etc was included in the overall DMF (drug master file) for the FDA. I must admit I still find the overall classification for the global market a little confusing.
The FDA routes submissions based upon the primary mode of action. For inhalers and similar types of devices, the primary mode of action is as a drug. Therefore, the applicable drug division will review first and then devices will become involved. For other products, the primary mode may be a device and a drug might be secondary in affect. An example is the addition of drugs to stents. The product is a device first in this case. For Europe the inhaler is a device, but classification is dependent upon if the manufacturer is selling the inhaler to another company for charging with drug or if the inhaler is already loaded with drug. It sounds like your company is loading the inhaler with drug and therefore treatment by the applicable competent authority would be similar to the FDA's approach.
The inhaler is not just packaging, because it dispenses measured doses. Believe it or not, a cup with lines for each milliliter is also considered a device. The lines may be different dependent upon the viscosity of the liquid. Inhalers are even more complex and there are many considerations that are well beyond the scope of liquid and pill formulations.
I won't comment on your submission(drug or device), but on the inhaler being treated as a medical devices...BIG YES!
Even if you submit your application as a drug, you still need to follow medical device QSRs as they apply to the inhaler device. All the bells and whistles of regulation that apply to a stent, orthopedic device, implant, etc... apply to your inhaler.
what about prefilled, disposable inhaler in Japan - are they regulated as medical devices with an own Submission, or rather as Container closure System as part of the drug application? Does anyone want to share their experience?