You should not use Caverject without the supervision of a specialist. Any doctor can do this, although it is the specialist in Urology, Andrology or Sexual Medicine who has the most experience to prescribe it. Like any other drug, we advise against trying to search unauthorized websites or the black market (milanuncios, wallapop, vivu or even the Deep Web) because you could be the victim of a forgery (we have seen very realistic ones) that could bring unpredictable consequences to your health. Not to mention, of course, economic scams that make you believe that you are going to receive a package for which you have paid that never arrives.
As long as the package has not been opened and the storage conditions have been adequate (the usual ones in most medicines), the expiry date itself is the one that marks this line from which it should not be used. Once it has been opened and "prepared" it should be used immediately (less than an hour).
If you find yourself in this case, perhaps your dysfunction case is not excessively serious, so rather than lowering the dose, with the help of a specialist overseeing the entire process, you could simply change the type of medication to one less invasive than the injection.
The ideal is to space the application in 24 hours, although it can be used earlier, but its effects can be noticeably reduced (and it is not advisable to increase the dose without medical supervision).
It is expressly contraindicated in the leaflet given by the manufacturer "if you suffer from an anatomical deformation of the penis, such as angulation, cavernous fibrosis or Peyronie's disease".