Found on Orthodixie (here) a prayer one says before partaking of Antidoron (nafora in Serbian):
[It is a pious custom to keep some holy bread and holy water in one’s icon corner — to consume, breaking the night’s fast, with one’s morning prayers.]
O Lord my God, may Thy holy gift and Thy Holy Water be unto forgiveness of my sins, unto enlightenment of my mind, unto strengthening of my spiritual and bodily powers, unto health of my soul and body, unto vanquishing of my passions and weaknesses, by Thy boundless merciful kindness, through the prayers of Thy Most-pure Mother and all Thy Saints. Amen.
Alongside this I was linked to Mystagogy (here) who posted the Life of St. Ahmed and the story of how Antidoron brought him to the Christian Faith:
The Holy New Martyr Ahmed was from Constantinople, having been reared in the ungodliness of the Muslims by his parents. By profession he was a copyist in the Great Archives. In accordance with Ottoman law, since he did not have a wife, he had a slave instead, a Russian woman. Another captive from Russia lived together with her, an old woman, also a slave. Both these women were very pious.1
On feast days the old woman would go to church. Taking the blessed bread, or antidoron,2 she would give it to the young woman to eat. The old woman would also bring her holy water to drink. Whenever this occurred and Ahmed was close to her, he would smell a beautiful and indescribable fragrance coming out of her mouth. He would ask her what she was eating to make her mouth smell so fragrant. Not realizing what was happening, the slave would say that she was not eating anything. However, he persisted in asking. Eventually she told him that she was eating the bread which had been blessed by the priests, which the old woman brought her whenever she returned from church.
On hearing this, Ahmed was filled with longing to see the Orthodox church and how Orthodox received this blessed bread. Therefore he summoned a priest and told him to prepare a secret place for him, so that he could go when the Patriarch3 was serving the Liturgy. When the appointed day arrived, dressed as a Christian,4 he went to the Patriarchate and followed the Divine Liturgy. While he was in church, he saw the Patriarch shining with light and lifted off the floor, as he came out of the altar and through the holy doors to bless the people. As he blessed, rays of light came from his finger tips, but though the rays fell on the heads of all the Christian, they did not fall on Ahmed’s head. This happened two or three times and each time Ahmed saw the same thing. Thus, Ahmed came to the faith. Without hesitation he sent for the priest, who gave him rebirth through baptism. Ahmed remained a secret Christian for some time.5However, one day Ahmed and certain noblemen were eating together. Afterwards they sat talking and smoking the narghile6, as is the custom. In the course of the conversation they began to discuss what was the greatest thing in the world. Each gave his opinion. The first guest said that the greatest thing in the world was for a man to have wisdom. The second maintained that woman was the greatest thing in the world. And yet a third said that the greatest thing in the world, and by far the most delightful, was pilaf with yogurt – for was this not the food of the righteous in paradise?
Then it was Ahmed’s turn. They all turned to him, asking him for his opinion on this matter. Filled with holy zeal, Ahmed cried out that the greatest thing of all was the Faith of the Christians. And confessing himself to be a Christian, he boldly censured the falseness and deception of the Muslims. At first, on hearing this the Muslims were aghast. Then, filled with unspeakable rage, they fell on the holy martyr and dragged him to a judge, so that he could be sentenced to death. Thus he received the crown of martyrdom, being beheaded by command of the ruler on the third day of May in the year 1682, at the place called Kayambane Bahche. Such was the blessed end of the Holy New Martyr, through whose holy prayers may we be deemed worthy of the Kingdom of God. Amen.