Fentanyl buccal tablets (FBTs) are a rapid-onset opioid indicated for breakthrough pain (BTP). However, some patients are not tolerable high-dose FBTs; therefore, FBTs titration is needed to optimize BTP management. In this study, we aimed to predict patients who could tolerate high-dose of FBT (400 mg or more at a time). Methods: A retrospective analysis was performed on advanced cancer patients treated with FBTs for BTP. For dose titration of FBT, the dose was continuously increased from 100

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... g up to 200, 400, and 800 mg to achieve the effective dose. Results: A total of 131 patients were analyzed. Males represented 62% of the patients, and the median age was 62 years. The most frequent effective doses of FBT were 200 mg (71 patients, 54%) and 100 mg (39 patients, 30%). The median value of morphine equivalent daily doses (MEDD) and daily FBT use were 60 mg/day (15 to 960) and three times per day, respectively. The final FBT dose had a reverse relationship with increasing patients' age (p ¼ 0.055); the younger had a higher final dose of FBT. The higher MEDD and daily FBT use, the final FBT dose significantly increased (p ¼ 0.003; p < 0.001, respectively). In multivariable analysis, male, younger age, and daily three or more use of FBT were independently associated with high-dose FBT. Risk scores were assigned based on the odds ratio from the final multivariable model, and patients were assigned into two groups: low tolerance (0-1 point) and high tolerance (2-3 points). According to the risk scoring groups, only one patient (3%) had a 400 mg of final FBT among the 33 low tolerance group, and most patients of final FBT 400 mg or higher were classified to high tolerance group (p ¼ 0.023). Conclusions: According to the dose relationship between the final FBT dose and the clinical features, three factors (sex, age, daily use of FBT) were independently associated with the final dose of FBT. A risk score model was developed and could help predict tolerance to high-dose FBT and guide the titration plan for BTP.