Is Amitriptyline Safe as Topical Treatment for Neuropathic Orofacial Pain?

Objectives: Amitriptyline is one of the systemic drugs of choice for Neuropathic Orofacial Pain. Some preliminary uncontrolled studies have identified a role for Amitriptyline as a compounded topical agent in the oral cavity, but no regulatory approval currently exists for this usage. This study investigates the effects of Amitriptyline on oral mucosa in vitro using a three-dimensional (3D) oral mucosa tissue model.
Methods: Amitriptyline was applied to a 3D oral mucosal model at a concentration (226µM) previously determined as the concentration released when used in orabase gel. A commercial, primary cell, model (MatTek) was used to examine Amitriptyline’s effects on cellular viability and cytotoxicity using colorimetric methods: alamarBlue^® and lactate dehydrogenase (LDH) assays respectively. Immunohistochemistry, employing an anti-caspase-3 antibody, was used to investigate Amitriptyline’s apoptotic effect. Exposure of 3D models to Amitriptyline was performed for 30 minutes twice daily (B.I.D. regimen) and three times daily (T.I.D. regimen) for three consecutive days.
Results: Results are presented as a mean percentage change (SEM) in the models exposed to Amitriptyline in comparison to the control models. The model exposed to the B.I.D. regimen demonstrated a significant reduction in viability [87% (2.6)] compared with the control [100% (0); p<0.05]. Apoptosis significantly increased in the exposed model in comparison with control: 1804% (1.1), 100% (0.4), respectively (p<0.05). LDH did not significantly change in the B.I.D. regimen (p>0.05).
In the model exposed to the T.I.D. regimen, a significant increase in apoptosis occurred [637% (1.2) compared with 100% (0.5), p<0.05], but there were no significant changes in viability or cytotoxicity.
Conclusions: Repeated exposure to topical Amitriptyline in vitro was associated with increased apoptotic activity in this tissue model, but there are limitations to the interpretation of the colorimetric methods in the 3D model. Even with limitations of this model, further safety research prior to clinical application to oral mucosa is needed.