I used the powder form of Caverject for a while. I can say that my experience was that the liquid , when refrigerated, will last much longer than what they tell you. I used it for up to 3 months. Also, I'd reconsider starting with .5ml, if that's actually what they told you. Is the powder 20mcg or 40mcg strength? What is the dilution ratio of the water to the powder? If I remember right, I added 1 ml water, but later started using 3ml water to cut the strength so it wasn't so potent. Makes a big difference which, as one is twice as strong as the other. In either case, I would start the first time with .1ml aka 10 units on the insulin syringe or .10cc. The Caverject is some strong stuff and you don't want your first experience to be a 4 hour erection and a visit to the ER for reduction. If you got the 40mcg strength and use .5ml injection, that's a really potent dose to take. Also, some people won't experience it, but don't be surprised if you experience aching and some amount of pain after you have injected. Caverject does that to most guys. It will be up to you to decide how much you are willing to experience to have an erection. If you don't want to continue with it, there is also Trimix and Bimix to use.
If you are using Caverject for the first time, there's some prep work to do. Get some of the true Sudafed, not the stuff they sell as a replacement now. You'll have to ask for it behind the counter. This is to be used if you have an erection lasting longer than 4 ours. At the 3 hour mark, take 2 of them to hopefully start the ending process. As I said, expect some aching, so you won't be caught by surprise. When you are done using the erection, leave it alone. Do not handle, stimulate or anything, as doing so will bring it back to full raging strenght for quite some time afterwards. Good luck and good luck...