I think it may have changed this year, but up to this year the cost of Nursing Home care (up to a max of €50000) was available as a relief, ie it was deducted from your income before arriving at your taxable income. Therefore if you paid tax at the higher rate 41%, you were getting relief at 41% of the nursing home cost. I think it has changed this year, so that irrespective of the tax rate you pay tax at 41% or 20%, its only available as a credit at the lower rate of 20%.
The fact that your claimimg it through using the MED1 shouldn't make any difference.