Testing pilocarpine drops for dry mouth in advanced cancer using n-of-1 trials: A feasibility study

Background: Dry mouth is a common and troublesome symptom in palliative care. Pilocarpine is a cholinergic agent that promotes salivation. Aim: This study aimed to test the feasibility of using n-of-1 trials to test pilocarpine drops compared to placebo, for patients of palliative care units with advanced cancer, who experienced dry mouth. Design: This was an N-of-1 study, in which each participant was offered three cycles of pilocarpine drops 4% (6 mg tds) (3 days) and placebo drops (3 days) in random order. Setting/participants: Participants were patients of specialist palliative care services with advanced cancer assessed as having a dry mouth, defined as having a score of ≥3 on an 11-point self-rated xerostomia numerical rating scale, from any cause. Patients self-completed a diary using validated symptom and quality-of-life scores. The randomisation order was unmasked at the end of each person's trial by a clinician independent of the trial to allow a treatment decisions for individual patients to be made. Results: Nine patients completed at least 1 cycle; 33 cycles of data were completed in total, comprising 438 doses of pilocarpine. Four patients completed the trial: two responded and two did not. Most withdrawals related to deteriorating condition, unacceptable toxicity, non-compliance with study procedures or withdrawal of consent. Many issues contributed to slow recruitment and high withdrawal rate. Conclusion: The formulation of pilocarpine drops proved unacceptable to most participants. More work is required to determine an appropriate formulation, dose and method of delivery and then a retest of pilocarpine drops for this symptom.