There is no reason to do an antibiotic designed for oral use by injection. Doxycycline is among drugs which have an expiration date that really matters. Don't use older doxycyline.
All pills that do get used IV require a micron filter to try to avoid serious complications that occur often when filters aren't used. I was going to close the thread but I may not have said enough about safety issues when injecting pills so I'll send to BDD. But why the hell do you want to inject doxycycline? If you need an antibiotic get it prescribed in the form you need it, getting a doc to correctly diagnose and prescribe for whatever is needed is another really good reason.
Homeless---------------------------->BDD