From what I gather (although I've not spent too much time on this) the patent is based on the below
delivery device (already patented by them some time ago) as well as the
strength or
naloxone dosage.
Learn about SYMJEPI, the compact and reliable epinephrine delivery option for treating allergic emergencies. Please see ISI and full PI on this website.
www.symjepi.com
But, you may say, there is already a similar device on the market (also patented) called Evzio (and a generic)? Well apparently not. Not anymore as of last year. Simply put: it was just no longer economically viable to continue producing these things (well: they were not making enough profit to put it another way).
workcompauto.optum.com
And maybe something important to be aware of:
"EVZIO (naloxone hydrochloride - solution;intramuscular, subcutaneous)
Manufacturer: KALEO INC
Approval date: April 3, 2014
Strength(s): 0.4MG/0.4ML (0.4MG/0.4ML) (discontinued)
Manufacturer: KALEO INC
Approval date: October 19, 2016
Strength(s): 2MG/0.4ML (2MG/0.4ML) (discontinued)
All of the above formulations have been discontinued.
Note: Fraudulent online pharmacies may attempt to sell an illegal generic version of Evzio. These medications may be counterfeit and potentially unsafe. If you purchase medications online, be sure you are buying from a reputable and valid online pharmacy. Ask your health care provider for advice if you are unsure about the online purchase of any medication."
My point being: not a good time to find out that your Evzio is a fake!
Generic drug availability, manufacturer information, and patent status on Evzio
www.drugs.com
Also and from what I gather: Kaleo (Evzio®) and Adamis (Zimhi®) had a go at each other (legally speaking) in 2019. Not sure what the outcome was.
Patent Lawsuit history for kaleo, Inc. v. Adamis Pharmaceuticals Corp. (1:19-cv-00917)
www.drugpatentwatch.com
Anyway. Whatever the case and outcome. One thing obviously led to another and you now have Zimhi® from Adamis!

Well maybe not yet i.e. according to Adamis' website they'll only begin marketing in the US in 2022.