Factors Associated With Nonadherence to S-1 in Docetaxel+S-1(DS) Therapy, an Adjuvant Treatment for Gastric Cancer

Background/Aim: In clinical practice, nonadherence to oral anticancer drugs due to adverse events or missed doses has become a significant challenge. In this study, S-1 nonadherence in postoperative S-1 plus docetaxel (DS) therapy for gastric cancer was examined in an oncology pharmacist outpatient clinic. Patients and Methods: Participants comprised patients who underwent postoperative DS therapy for gastric cancer from November 1, 2015 to April 30, 2021 at the Cancer Institute Hospital of the Japanese Foundation for Cancer Research. The number of S-1 nonadherences and reasons for nonadherence in 1-7 courses were extracted from electronic medical records. The percentage of S-1 nonadherence was defined as the ratio of the number of S-1 nonadherences to the number of prescribed S-1 administrations per course. Results: The total number of patients was 90. The percentage of S-1 nonadherences increased significantly to 7.4% in the second course compared with 3.9% in the first course (p<0.05). In the 222 cases of S-1 nonadherence, the main reasons for nonadherence were nausea/vomiting (18.9%) and missed doses (17.6%). The mean number of S-1 nonadherences per course was significantly higher for patients living alone (6.6) than for patients not living alone (2.9, p<0.01). The rate at which pharmacists checked the remaining S-1 medications and proposed prescriptions to doctors was 45.6%. S-1 nonadherence occurred due to adverse events and missed doses, with the second course being the period of highest frequency. Conclusion: Information on S-1 nonadherence was revealed by conducting an oncology pharmacist outpatient clinic. Improved side-effect management and medication support is expected to contribute to reducing nonadherence in the future.