Real-World Prescribing Patterns and Treatment Continuation of Amitriptyline Monotherapy and Aripiprazole Augmentation for Medically Unexplained Oral Symptoms/Syndromes in Japan

<b>Background:</b> Medically unexplained oral symptoms/syndromes (MUOS), such as Burning Mouth Syndrome and Persistent Idiopathic Facial Pain, present significant management challenges due to the lack of standardized treatments and high-level evidence. While pharmacotherapy is often employed, real-world data on treatment adherence-a pragmatic proxy for effectiveness and tolerability-remain sparse, especially in Japan. This study aimed to describe the real-world prescribing patterns of antidepressants and dopamine receptor partial agonists (DPAs) for MUOS and retrospectively investigate their association with treatment continuation. <b>Methods:</b> This retrospective observational study analyzed data from patients initiating pharmacotherapy for MUOS at a specialized clinic in Japan (April 2021-March 2023). We used Cox proportional hazards models to evaluate treatment continuation for amitriptyline monotherapy and antidepressant-aripiprazole adjunctive therapy. The primary outcome was the time to discontinuation. Dosage effects were modeled using B-splines to capture nonlinearity. <b>Results:</b> Among 702 MUOS patients who started pharmacotherapy, 493 received amitriptyline as the first prescription, and 108 received aripiprazole as an adjunctive therapy. For amitriptyline monotherapy, a nonlinear relationship was observed between dosage and discontinuation risk, with a relatively lower hazard around 25 mg/day across age groups. In the antidepressant-aripiprazole adjunctive group, the overall hazard ratio for discontinuation was higher (HR = 4.75, <i>p</i> < 0.0005) compared to non-adjunctive therapy, likely due to indication bias reflecting more treatment-resistant cases. However, within the aripiprazole adjunctive group, a U-shaped relationship was identified between maximum aripiprazole dosage and discontinuation risk, with the lowest hazard (HR ≈ 0.30) observed at approximately 1.7-1.8 mg/day. Mild side effects such as drowsiness, dry mouth, constipation, tremor, insomnia, and weight gain were noted, but no severe adverse events occurred. <b>Conclusions:</b> This real-world data analysis suggests specific dosage ranges (amitriptyline ≈ 25 mg/day; aripiprazole augmentation ≈ 1.7-1.8 mg/day) are associated with longer treatment continuation in MUOS patients. Treatment continuation reflects a crucial balance between symptom relief and tolerability, essential for managing these chronic conditions. It is critical to emphasize that these findings are descriptive and observational, derived from a specialized setting, and do not constitute prescriptive recommendations. They highlight the importance of individualized dosing. Definitive evidence-based strategies require validation through prospective randomized controlled trials.