Cynavit Cyanocobalamin Hydroxocobalamin
ModeratePeople who have been treated with chloramphenicol may not respond well to cyanocobalamin, so it may work less well for them. This is stated in the hydroxocobalamin leaflet as a caution about cyanocobalamin, and it doesn't say how likely this is or what to do about it.
These medicines are often taken together with some care. Your doctor may change a dose, space them apart or check on you more often. Make sure your doctor and pharmacist know you take both.