If the root canal treated tooth has become infected then either you have to get it pulled out or you can go for re root caal treatment. In re root canal treatment the root canal is done again. Taking antibiotics can give you the temporary relief but it can not remove the infection. The problem will reoccur after some time. If you want to know more about the re root canal treatment you can visit the following link..........http://www.identalhub.com/article_root-canal-re-treatment-304.aspx