Hi m franco, welcome to the community.  MC pays 80% of the assigned amount.  You'll have to ask MC what the assigned amount is though.  If her Humana is an HMO or PPO they should be able to tell you what the copay is.  If MC (original medicare) is still the primary insurance then they pay the figure above.  If Humana is primary, then you just pay whatever they don't pay and I don't know what that is.

You should be able to call an infusion center, where they give Reclast, tell them what insurance she has and have them look it up.  It gets very confusing when you have Medicare and a supplement, or Medicare (original) with a Medigap plan.  Since I'm not sure what scenario your mom has, you should be able to find out through Humana, and if that doesn't work then through MC.  Typically if you are still using MC and have a Medigap plan, MC pays 80% of the assigned amount and Humana would pay 20% of the assigned.  The rules change if Humana is the primary, so call all three places to get the best idea of what the charge will be.

Good luck and let us know what you find out, since there are so many differing options of insurance with MC.