Akihiko Akamine,1 Yuya Nagasaki,2 Atsushi Tomizawa,2 Katsuya Otori2,3 1Department of Pharmacy, Doujin Hospital, Okinawa, Japan; 2Department of Pharmacy, Kitasato University Hospital, Kanagawa, Japan; 3Research and Education Center for Clinical Pharmacy, Division of Clinical Pharmacy, Laboratory of Pharmacy Practice and Science 1, Kitasato University School of Pharmacy, Tokyo, JapanCorrespondence: Akihiko Akamine, Department of Pharmacy, Doujin Hospital, 1-37-12 Gusukuma, Urasoe, Okinawa, 901-2133, Japan, Tel +81-98-876-2212, Fax +81-98-874-7034, Email a-aka@kitasato-u.ac.jpPurpose: The risk factors for non-adherence to pharmacist or non-pharmacist explanations of preoperative medication discontinuation are unknown. The primary outcome of this study was to determine whether the final explainer’s occupation was a risk factor for non-adherence. The secondary outcomes were to determine the risk factors for non-adherence after limiting the departments or adjusting for age.Patients and Methods: We retrospectively examined the data (including patient age, sex, prescription medications, comorbidities, presence of roommate, and number of days between receiving explanation and surgery) of 1132 patients on medications that could affect surgery at a Japanese university hospital between April 1, 2017, and March 31, 2020. The primary endpoint was whether the occupation of the last person explaining medication discontinuation to the patient was an independent risk factor for non-adherence (age ≥ 65 years vs < 65 years). Secondary endpoints included subgroup analyses in urological, gastrointestinal, and otolaryngological areas, as well as a sensitivity analysis (age as a continuous variable) to confirm the validity of the primary endpoint results. A multivariate binary logistic regression identified independent non-adherence risk factors.Results: The main analysis showed that discontinuing two or more medications was a risk factor for non-adherence (adjusted odds ratio (AOR): 1.67; 95% confidence interval (CI): 1.13– 2.47; p = 0.01). However, in analyses coordinated by department (urological, gastrointestinal, and otolaryngological), ≥ 65 (versus < 65) years of age was determined as a risk factor for increased nonadherence (AOR: 2.27, 95% CI: 1.11– 4.63; p=0.024). Age-adjusted analysis (continuous variables) showed similar results to the primary endpoint (AOR: 1.68, 95% CI: 1.14– 2.49, p = 0.009).Conclusion: Two or more medications, and not the final explainer’s occupation, were associated with pre-surgery medication non-adherence. To prevent non-adherence, pharmacists and non-pharmacists should educate patients about preoperative medication discontinuation. These findings could help identify high-risk non-adherence patients.Plain Language Summary: At Kitasato University Hospital, pharmacists and non-pharmacists explain before surgery that patients scheduled for surgery should discontinue medications that could affect surgery. However, there are patients who fail to follow these explanations precisely, but the risk factors have not yet been identified. This study examined risk factors for patients who failed to comply with explanations from a pharmacist or non-pharmacist regarding the use of medications that could affect surgery. Risk factors were examined using a statistical method for identifying risk factors by considering patients’ age ≥ 65 (versus < 65) years, sex, the job title that explained the instructions to the patient, number of medications to be discontinued before surgery, and number of days between instructions and surgery as risk factors. Based on pharmacist/non-pharmacist explanations, the statistical analysis revealed that patients taking two or more medications that could affect surgery may be a risk factor for non-adherence to medications that should be discontinued before surgery. To improve medication adherence, pharmacists and non-pharmacists should be aware of the patient’s non-adherence risk factors, repeatedly explain them to the patient, and help the patient understand that failure to comply with the explanation increases surgical cancelation and intraoperative bleeding risks.Keywords: medication adherence, hematologic agents, pharmaceutical service