Here is link to US patent application from MVP for new Penthrox...

Here is link to US patent application from MVP for new Penthrox inhaler.
https://patents.google.com/patent/US20180200459A1/en
The new inhaler has a few advantages from my reading of the document. First the patient has more control over the rate of release of the pain relief, second there is a more even release of pain relief over a longer period, third there is less emission of Penthrox vapour into air.
Is it likely/ possible that one of the FDA concerns about Penthrox was the efficiency of current Green Whistle and the new device is the result of MVP trying to address FDA concerns? Guess we will find out if we ever get to read the  pending FDA letter to MVP.
One para from patent application says......"In both cases, the devices delivered methoxyflurane. However, while the initial first breaths concentration of methoxyflurane delivered by both devices starts off at the same level, the Prototype device was shown to maintain a steady state level over a longer period of time than the Green Whistle device. Accordingly, the Prototype device was shown to deliver a lower concentration of methoxyflurane for a longer duration. In contrast, the Green Whistle device was shown to deliver methoxyflurane at a higher steady state level for a shorter duration initially which was then followed by a rapid reduction below the steady state concentration of methoxyflurane achieved by the Prototype device."