Sialorrhea Successfully Treated by the Combined Use of Selective M1 and M3 Muscarinic Acetylcholine Receptor Antagonists

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Sialorrhea is often treated with anticholinergic agents, but they can have undesirable side effects such as drowsiness, sedation, and constipation. Effective medication that acts selectively on the salivary glands is needed. We report the case of a patient with sialorrhea who was successfully treated by the combined use of pirenzepine and solifenacin (M1 and M3 muscarinic receptor antagonists, respectively). The patient was a 51-year-old man with mean unstimulated and stimulated salivary flow rates per 10 min of 6.1 mL and 41.7 mL, respectively (both were measured three times). ^99mTcO⁴⁻ salivary gland scintigraphy revealed characteristic spontaneous saliva secretion without stimulation. He was treated with Scopolia extract, escitalopram, solifenacin succinate, and the combined administration of solifenacin succinate and pirenzepine. A statistically significant decrease was observed from the pre-medication unstimulated and stimulated salivary flow rates only following the combined administration of solifenacin and pirenzepine. The major muscarinic receptor subtype expressed in the salivary glands is M3; however, M1 is also present. A study using knockout mice demonstrated that the presence of either M1 or M3 receptors was sufficient for salivation. Thus, the combined use of selective M1 and M3 antagonists could provide a good treatment option for sialorrhea.