Objective: To describe a case of clozapine-induced sialorrhea alleviated by immediate-release oxybutynin.
Case summary: A 53-year-old female with schizoaffective disorder-bipolar type was admitted to a psychiatric unit and initiated on clozapine. During titration to a dose of 300 mg daily and despite taking concomitant oral benztropine 1 mg twice daily, the patient began to experience mild sialorrhea. The sialorrhea became profuse when the clozapine dose reached 400 mg daily, and the patient was routinely seen with a saliva-soaked shirt. Additionally, she had become self-conscious and wanted to stop clozapine therapy. Immediate-release oxybutynin 5 mg daily was started, resulting in significant reduction of the sialorrhea within 24 hours. The patient was discharged on clozapine 300 mg daily, risperidone 6 mg at bedtime, immediate-release oxybutynin 5 mg twice daily, and oral benztropine 1.5 mg daily, with only mild sialorrhea.
Discussion: It is unknown why clozapine induces sialorrhea. One speculation is that clozapine interrupts muscarinic receptor homeostasis. Immediate-release oxybutynin is an anticholinergic agent with high affinity for salivary gland M₃ receptors that may have restored muscarinic receptor imbalance in our patient. N-Desethyl-oxybutynin, an active metabolite of oxybutynin, is largely responsible for oxybutynin's anticholinergic activity. The activity of oxybutynin and its metabolite may result in dry mouth in over 80% of patients taking the immediate-release formulation, while producing dry mouth in only 40% and 7.5% of patients taking the extended-release and topical formulations, respectively.
Conclusions: To our knowledge, this is the first report of immediate-release oxybutynin successfully reducing clozapine-induced sialorrhea. If oxybutynin is considered for this indication, use of the immediate-release formulation seems prudent. Additional data, including randomized controlled trials, are needed to confirm whether immediate-release oxybutynin has a significant role in the management of this stigmatizing adverse effect.