# Pharmacological Insights into Optimal Dosing in Burning Mouth Syndrome: A Narrative Review of the Non-Linear Actions of Amitriptyline and Aripiprazole

## TL;DR

This review explains how low doses of amitriptyline and aripiprazole can effectively treat Burning Mouth Syndrome due to their unique interactions with brain receptors, requiring personalized dosing for optimal results.

## Contribution

The paper introduces a personalized therapeutic window concept for BMS treatment, based on non-linear drug responses and receptor interactions.

## Key findings

- Amitriptyline at low doses (e.g., 25 mg) acts as an NMDA receptor antagonist, reducing central sensitization in BMS.
- Aripiprazole shows sustained efficacy at low doses (1.7–1.8 mg/day) due to dopamine D2 receptor partial agonism and serotonin receptor interactions.
- Non-linear dose–response is explained by receptor desensitization, multiple binding sites, and hormesis.

## Abstract

Background: Burning Mouth Syndrome (BMS) is a nociplastic pain condition characterized by altered central nervous system pain processing, significantly impacting patient quality of life. Pharmacological management often involves amitriptyline (monotherapy) and aripiprazole (for refractory cases) in Japan. However, the therapeutic efficacy of these drugs in BMS frequently exhibits a non-sigmoid (U-shaped or bell-shaped) dose–response relationship, indicating a clinically effective dose that is often considerably lower than those used for their primary indications and challenging conventional pharmacological assumptions. Method: This paper synthesizes existing pharmacological knowledge to elucidate the mechanisms underlying the non-dose-dependent actions of amitriptyline and aripiprazole in BMS. It focuses on their specific interactions with key neurotransmitter systems and receptors, particularly N-methyl-D-aspartate (NMDA) receptors and dopamine D2 receptors, to explain the observed non-linear dose–response and the importance of identifying a personalized therapeutic window. Result: Amitriptyline demonstrates efficacy in BMS at low doses (e.g., 25 mg), primarily through its action as an NMDA receptor antagonist via calcium-dependent desensitization and open-channel block, addressing central sensitization. Its effects are distinct from its antidepressant actions, and the “serotonin paradox” highlights the complexity of serotonin’s role in pain. Aripiprazole, utilized for refractory BMS, acts as a dopamine D2 receptor partial agonist, leading to a non-linear dose–response where sustained therapeutic effect is observed at specific low doses (e.g., 1.7–1.8 mg/day). This non-linearity is attributed to partial agonism, alongside interactions with serotonin 5-HT1A and 5-HT2A receptors. The general non-dose-dependency for both drugs is further explained by phenomena such as multiple binding sites with differing affinities, receptor desensitization/downregulation, activation of counter-regulatory mechanisms, and hormesis. Discussion: The observed non-linear dose–response curves for amitriptyline and aripiprazole in BMS underscore the inadequacy of a “one-size-fits-all” treatment approach. This necessitates a shift towards personalized medicine, which considers individual patient factors including pharmacogenomics, comorbidities, age, organ function, and psychological/social profiles. The true “personalized therapeutic window” is a balance between achieving significant pain relief and minimizing adverse effects, emphasizing careful titration and patient-centered care. Conclusions: The pharmacological actions of amitriptyline and aripiprazole in BMS are not linearly dose-dependent, but rather exhibit a personalized therapeutic window driven by complex interactions with NMDA and D2 receptors and adaptive physiological responses. This intricate pharmacological landscape mandates a personalized medicine approach to optimize treatment outcomes, improve patient adherence, and enhance the quality of life for individuals suffering from this challenging nociplastic pain condition.