Metastatic HER2-positive breast cancer is an incurable disease with a poor prognosis. This article presents a critical appraisal of two treatments commonly used in the treatment of metastatic HER2-positive breast cancer: the oral chemotherapy drug, capecitabine, and the monoclonal antibody, trastuzumab. What follows is a critical discussion of the pharmacotherapeutics of capecitabine and trastuzumab, which considers their use both as single agents and as a combination regimen in the treatment of metastatic breast cancer. The implications of side effects of these drugs are discussed, both individually and in combination, as are the challenges these bring to the prescriber. The article evaluates the use of these agents and concludes that the combination of capecitabine and trastuzumab is an attractive treatment option for patients and for the prescriber.