Long story short I accidentally used a needle that had touched the ground (cement) to inject my old man's pentosan this morning. I knew what I had done as soon as I stuck it in as it was a little bent at the hub. I called the vet and requested a call back but am debating giving him a shot (with a new needle!) of gentocin while I wait. Does that work on clostridial bacteria or whatever it is that eats a hole in them? I am not very good at waiting patiently!
He had a tiny spot of dried blood from the first injection so I have the Pen right next to that. When I took the needle out there was a small lump. At least I know this lump is from the Pen and not infection since it wasn't there a second earlier but I guess I need to monitor it to make sure it doesn't get bigger or hot etc. The vet said to follow up with 3 days of SMZ's.
I would wager that unless you're doing something to prep the skin first the odds of an infection from a needle briefly touching the ground are approximately the same as the odds of infection with no skin prep. Which are low. Glad you dodged a bullet!