Low-Dose Amitriptyline: A Potential Therapeutic Option for Chronic Pain in Older PeopleTakayuki Suga, DDS, PhD1; Trang Thi Huyen Tu, DDS, PhD1,2; Motoko Watanabe, DDS, PhD1; Takahiko Nagamine MD, PhD1,3; and Akira Toyofuku, DDS, PhD11 Department of Psychosomatic Dentistry, Graduate School of Medical and Dental Sciences, Institute of Science Tokyo2 Department of Basic Dental Sciences, Faculty of Odonto- stomatology, University of Medicine and Pharmacy at Ho Chi Minh City, Ho Chi Minh City, Vietnam3 Department of Psychiatric Internal Medicine, Sunlight Brain Research Center, Yamaguchi, Japan.Word count:798Acknowledgements: noneConflict of interest statement: There are no conflicts of interest to declare.Keywords: psychopharmacology, safety Pharmacology, chronic pain, antidepressive agents, older adultCorrespondence to:Takayuki Suga, DDS, PhD1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8510, Japan.Phone number: +81358035898; Fax: +81358035898; Email: suga.ompm@tmd.ac.jpThe use of antidepressants in older adults with chronic pain is controversial. We found Dr. Narayan et al.’s article, titled “Efficacy and Safety of Antidepressants for Pain in Older Adults: A Systematic Review and Meta-Analysis,” on the use of antidepressants in older people with chronic pain to be highly engaging. (Narayan et al., 2024) They conducted a systematic review and meta-analysis on the efficacy and safety of antidepressants for chronic pain in older people. Due to various limitations, they concluded that the benefits and harms of antidepressant medicines for most types of chronic pain, especially knee OA, are unclear.Conducting clinical research with older adults poses challenges, often excluding them due to pre-existing conditions. Randomized controlled trials (RCTs) in this population are particularly difficult for several reasons:1. Comorbidities and Polypharmacy: older people often have multiple chronic conditions and take various medications, complicating group allocation, the isolation of the intervention’s effects and increasing the risk of drug interactions.2. Heterogeneity and Follow-up Challenges: Due to mobility impairments and other factors, it is difficult for older people to make regular visits to hospitals conducting RCTs, leading to high dropout rates.3. Ethical Considerations: The older people are often regarded as a vulnerable population, requiring ethical considerations when involving them in risk-related interventions.Despite these challenges, studies using real-world data suggest that, when used carefully, antidepressants might help manage chronic pain in older adults, particularly for conditions like burning mouth syndrome (BMS).BMS, a common type of chronic orofacial pain affecting mainly postmenopausal women, has uncertain pathophysiology.We previously reported that low doses of amitriptyline are effective in managing pain in older people with BMS. (Suga et al., 2019) Furthermore, even in patients over 80 years old, amitriptyline demonstrates efficacy when used in low doses with careful administration. (Watanabe et al., 2022) Regarding common side effects, managing these side effects in elderly patients will be effective through regular visits and examination. (Suga et al., 2019; Watanabe et al., 2022) Hence, it is crucial to monitor for anticholinergic side effects such as drowsiness, dry mouth, and constipation, as well as potential falls due to dizziness and any changes in cognitive function in clinical assessment.A therapeutic window exists for the dosages of amitriptyline that are effective in managing chronic pain, indicating that its efficacy is not dose-dependent. (Nagamine, 2024) In contrast to the doses used in psychiatry for depression (typically 100 mg/day or more), amitriptyline is effective at doses of 5-20 mg/day in the treatment of BMS. The use of amitriptyline at this dosage is considerably lower than the doses employed in the RCTs included in the authors’ study, suggesting a reduced risk of side effects and withdrawal symptoms.The challenges of administering antidepressants to older people with chronic pain are not limited to concerns about side effects but also encompass issues related to their overall efficacy in this population. Serotonin’s role in pain modulation is complex, as it can either exacerbate or alleviate pain depending on the receptor subtype activated. This bidirectional effect is attributed to the distinct pathways involved in serotonin-mediated pain processing, with some receptors promoting analgesia and others enhancing nociception. (Bannister & Dickenson, 2016) Additionally, the elevation of serotonin levels might disrupt the delicate equilibrium with dopamine, thus hindering pain inhibition via the reward pathway. Therefore, increasing serotonin levels alone may exacerbate pain rather than produce therapeutic benefits.Moreover, chronic pain modulation involves not only serotonin but also other monoamines, such as dopamine and noradrenaline. Consequently, antidepressants that modulate serotonergic, noradrenergic, or dopaminergic pathways may exhibit therapeutic potential in managing chronic pain. (Bannister & Dickenson, 2016) This is also reflected in the study by Narayan et al., which demonstrated the efficacy of duloxetine, a dual serotonin and noradrenaline reuptake inhibitor, albeit with a modest effect size. Amitriptyline, which similarly targets both serotonin and noradrenaline, and to some dopamine transporters, may offer superior efficacy compared to other antidepressants. However, as previously mentioned, its therapeutic effect does not appear to be dose-dependent, suggesting that there may be an optimal therapeutic window at lower doses. Although not specifically in older people, other reports have also demonstrated the effectiveness of low-dose amitriptyline (5-25 mg/day) in managing conditions such as lower back pain, chronic neck pain, and chest pain. (Maarrawi et al., 2018; Park et al., 2013; Urquhart et al., 2018) Given the above, it is conceivable that low doses of certain antidepressants, such as amitriptyline, may be effective and safe for patients with other types of chronic pain. Research on the use of antidepressants for chronic pain in older people is still limited; therefore, as the authors have pointed out, there is a need for more prospective studies and numerous real-world investigations. In conclusion, careful clinical management and the accumulation of treatment data are essential for the effective treatment of chronic pain in older people using antidepressants.ReferencesBannister, K., & Dickenson, A. H. (2016). What do monoamines do in pain modulation? Curr Opin Support Palliat Care , 10 (2), 143-148. https://doi.org/10.1097/SPC.0000000000000207Maarrawi, J., Abdel Hay, J., Kobaiter-Maarrawi, S., Tabet, P., Peyron, R., & Garcia-Larrea, L. (2018). Randomized double-blind controlled study of bedtime low-dose amitriptyline in chronic neck pain. Eur J Pain , 22 (6), 1180-1187. https://doi.org/10.1002/ejp.1206Nagamine, T. (2024). Amitriptyline at low dose for burning mouth syndrome. Oral Diseases , 30 (7), 4650-4652. https://doi.org/10.1111/odi.14966Narayan, S. W., Naganathan, V., Vizza, L., Underwood, M., Ivers, R., McLachlan, A. J., Zhou, L., Singh, R., Tao, S., Xi, X., & Abdel Shaheed, C. (2024). Efficacy and safety of antidepressants for pain in older adults: A systematic review and meta-analysis. Br J Clin Pharmacol . https://doi.org/10.1111/bcp.16234Park, S. W., Lee, H., Lee, H. J., Park, J. C., Shin, S. K., Lee, S. K., Lee, Y. C., & Kim, J. E. (2013). Low-dose amitriptyline combined with proton pump inhibitor for functional chest pain. World J Gastroenterol , 19 (30), 4958-4965. https://doi.org/10.3748/wjg.v19.i30.4958Suga, T., Takenoshita, M., Watanabe, T., Tu, T. T. H., Mikuzuki, L., Hong, C., Miura, K., Yoshikawa, T., Nagamine, T., & Toyofuku, A. (2019). Therapeutic Dose of Amitriptyline for Older Patients with Burning Mouth Syndrome. Neuropsychiatric Disease and Treatment ,Volume 15 , 3599-3607. https://doi.org/10.2147/ndt.S235669Urquhart, D. M., Wluka, A. E., van Tulder, M., Heritier, S., Forbes, A., Fong, C., Wang, Y., Sim, M. R., Gibson, S. J., Arnold, C., & Cicuttini, F. M. (2018). Efficacy of Low-Dose Amitriptyline for Chronic Low Back Pain: A Randomized Clinical Trial. JAMA Intern Med ,178 (11), 1474-1481. https://doi.org/10.1001/jamainternmed.2018.4222Watanabe, M., Takao, C., Liu, Z., Nayanar, G., Suga, T., Hong, C., Tu, T. T. H., Yoshikawa, T., Takenoshita, M., Motomura, H., Nagamine, T., & Toyofuku, A. (2022). The Effectiveness and Adverse Events of Amitriptyline and Aripiprazole in Very Elderly Patients With BMS.Frontiers in Pain Research , 3 . https://doi.org/10.3389/fpain.2022.809207