Yeah, like other amphetamines, dexamphetamine is water soluble (1:10 Dexamphetamine Sulfate in Water), so you can dissolve the drug from the tablet in water and inject.
Crush the tablets up and let them sit in a bit of water, mix it around a few times to encourage dissolution. The volume of water you use will be dependent upon the number of tablets you want to prepare, adding enough water to avoid an excessively gluggy consistency, which would make it hard to draw the juice through a filter and into a syringe. (If you are gonna inject a relatively large volume of liquid, do it slowly so that the vein has time to take in the fluid, and that way none will flush out of the entry hole and into surrounding tissue).
A really important thing to remember is to filter the mix before you shoot - the tablets contain 5mg dexamphetamine as well as other excipients that are not water soluble and are likely to cause problems if you inject them.
---Your best bet is to source a 0.22 micron (removes gack/particles and most microbes) wheel filter from a pharmacy somewhere in your area, or try your local user's association or online if none are available.
Other pointers include general good practice with intravenous injection, e.g. always use sterile fits, wash hands and swab the injection site before and after puncture, try to find and use Sterile Water for Injections (comes in little vials), etc.
Also expect your veins to constrict after you inject the dex; it will make most of the veins around the injection site tighten up and they will shrink, so if you want to boost with another shot you may have more trouble trying to hit a vein.
**Inject slowly.
**Please filter, you will fuck up your delicate blood vessels if you don't bother to do that, and you'll lose your chance to continue enjoying drugs into old age.....