While preparing an anticancer drug, even if it is an expensive molecular target drug, the remainder is not divided and saved for use in other patients; instead, it is discarded, resulting in waste of medical resources. In this study, we examined the economic loss in terms of medical costs by calculating the discarded amounts of 12 commonly used molecular target drugs at Ogaki Municipal Hospital, Japan between January 2012 and December 2014. We found, on average, that drugs valued at ¥ 52,593,182 were discarded annually. In particular, the discarded amounts of relatively expensive drugs, such as bevacizumab, bortezomib, and rituximab, were valued at ¥ 16,646,300, ¥ 15,866,289, and ¥ 8,401,324, respectively. Among these, the average amount of waste per administration of bortezomib was particularly expensive, at a cost of ¥ 67,325. Bortezomib is a commonly used treatment, resulting in excessive cumulative discarded cost. In an effort to save cost, we should consider using small capacity standard injections. Development of a simulation that used the remaining drug contents from only 1 day showed that bevacizumab alone accounts for an average cost saving of ¥1 2,542,191(75.3%) per year. This study suggests that effectively utilizing the remaining drug contents would ensure efficient use of medical resources, thereby reducing economic losses.