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

Dry mouth is a common and troublesome symptom in palliative care. Pilocarpine is a cholinergic agent that promotes salivation.

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.

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.

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.

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.

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.