B12d ships two types of injectable B12 - hydroxocobalamin, and methylcobalamin.
Hydroxocobalamin is in a salt as hydroxocobalamin acetate. It's the form that most people find the most useful, because it converts easily into both methylcobalamin and adenosylcobalamin, which two forms you need for all of the body's functions.
Methylcobalamin is in a salt with natrium chloride. It's a different form, and whereas quite a lot of people can convert this to adenosylcobalamin, a few people can't and they should take adenosylcobalamin tablets (eg dibencozide) at the same time as the injections.
Incidentally, there's no harm in taking tablets at the same time as injections. You can always buy the tablets from lots of online shops.
As far as i can find out, there are no strange solvents or anything else in the B12 we send out. We have had people asking, so it's possible/ probable that some manufacturers make their injectable B12 with strange things. Although i doubt that any B12 within the European Union (including UK) has anything dangerous in it. We were sure that USA methylcobalamin was also safe, but we couldn't buy it any more because European Union said that it couldn't confirm this - better safe than sorry, every time!