How do I handle a case where the medicare Part b premiums are reimbursed as part of a retirement medical plan?

[DoninGA]

If you are referring to a HRA, Health Reimbursement Arrangement, where your deductible medical expenses that you have paid with out of pocket funds are reimbursed by the HRA, then you do not enter any medical expenses where you have been reimbursed.  The HRA reimbursement is not entered on your tax return.