Looks like you max out the credit first and then medical expenses above the credit limit can be used for itemized deductions.
Medical expenses.
Some expenses for the care of qualifying persons who aren't able to care for themselves may qualify as work-related expenses and also as medical expenses. You can use them either way, but you can't use the same expenses to claim both a credit and a medical expense deduction.
If you use these expenses to figure the credit and they are more than the earned income limit or the dollar limit, discussed later, you can add the excess to your medical expenses. However, if you use your total expenses to figure your medical expense deduction, you can't use any part of them to figure your credit. For information on medical expenses, see Pub. 502, Medical and Dental Expenses.
https://www.irs.gov/publications/p503#en_US_2018_publink1000203342
