I just read this over at Medline. It mentions limiting the amount of hours per day. It also mentions that the positive effect may diminish with long term use. This info was last updated in 2015 and I didn’t see any mention of edema. New uses for existing drugs is fairly common.
Indeed you must limit the Nitro patch to a max 14 hours a day (usually not a problem).
I’ve been on Nitro for 6 weeks now and there’s absolutely no reduction in efficacy.