I think this is a great idea, and I've collected a few pieces of info for you.
- The University of Dublin requires that you speak three languages: English, Irish and a third language. Since no-one except the Irish speaks Irish so well as to be able to attend classes in it, I guess this college will not be the most diverse, and very likely not be suitable for you.
- The NUI Galway is much more welcoming towards international students. I think with a BSc in biology, you meet their entry requirements. The complete list is here: http://www.nuigalway.ie/medicine/entry.html
- The University of Cork is also much nicer than the one in Dublin, I think. They even have a special office for international students to assist them in the application process. And the best part is: They have their own US/Canadian website, to be found here: http://www.ucc.ie/en/international/USCanadianWebsite/
- The Royal College of Surgeons in Ireland is also a nice choice, to be found at http://www.rcsi.ie/
So, to sum up and answer your first question: Yes, it is possible.
Considerations, well, that is something different. Ireland is simply not around the corner, you can't go home over the weekend, but since it is one of the most beautiful countries in Europe, I don't believe you will be deterred by that. You need to consider other, more practical things:
- Where will you live? On-campus accommodation is not my first choice, to be perfectly honest. Sometimes you just have to get away. A host family can be very nice for a sociable, good-hearted person. Living alone is expensive and can be tedious, but since my living-together experiment with a person I hardly knew, it is my favourite.
- Where will you get money from? Education isn't available for free in Ireland, either. And you will need a place to sleep and some food and so on. With the busy schedule of a full-time medical student, will you be able to squeeze in a job? Or are you maybe eligible for a scholarship? Start looking into these now, there may be deadlines to keep in mind.
- What about health cover? Health cover is sort of expensive in Ireland, and not compulsory, but in case something happens, the costs can quickly amount to a few hundred Euros for simple treatments. I would say, take the safe way.
- Good news is: You don't have to bother getting a visa. As a US citizen, you are free to enter the country.
Um, I think I covered the most important steps... Hope it is of some use!