I haven't heard of
Lantus causing this kind of problem. I would think that the cause is something else, especially since he has used
Lantus before. Apparently oedema (Swelling due to the retention of fluids in the tissues) is a know adverse reaction to Remeron. So he might want to try stopping the Remeron and seeing if the swelling goes away. But get him to go back on the
Lantus first, so that you can isolate the cause.
Mark