I have two things to add to post. First I have used trimix in past and I must say it works. As has been said dosage must be set for the individual, very important. Trimix would keep me erect for 2-2 half hours whether I would cum or not. I enjoyed the constant erection. However, it was expensive for me so I gave it up. Now as a total bottom, erections mean little to me.
Secondly, as has been posted this can be dangerous if not dosed properly. I have two friends who got together, one is a dom the other a pet. The dom injected caverjet into the pet and because he knew nothing about the dosage the pet stayed erect for well over four hours and they ended up in ER where they had to drain the pets penis. Subsequently, ( this was around 2010) the pet has never been able to have an erection. He suffers mentally from this as you can imagine. The dom as of this past fall ended up in jail for messing up castrating a willing guy who had to go to ER,