Trial of Ondansetron as a Parkinson's HAllucinations Treatment

TOPHAT (Trial of Ondansetron as a Parkinson's HAllucinations Treatment) is a double blind, individually randomized, placebo-controlled, parallel group, flexible dose trial of ondansetron (8-24mg/day) as a treatment for Parkinson's hallucinations, with a 12-week primary outcome and follow-up to 24 weeks.

This study investigates whether ondansetron, a drug used to treat post-operative sickness, has a meaningful treatment effect on Parkinson's hallucinations, and whether the drug is safe and cost effective for use in the NHS. We will compare ondansetron to placebo (a tablet that looks identical but contains no drug) over 12 weeks treatment, with follow up (once treatment ends) for a further 12 weeks. Assessments of symptoms will be carried out during treatment (after 6 and 12 weeks), and once treatment ends (18, 24 weeks), to measure hallucinations, delusions (false beliefs), Parkinson's symptoms (tremor, anxiety, sleep disturbance), memory, quality of life, possible side-effects such as constipation and headache, and the proportion of people who drop out due to side effects, or require additional treatment for their hallucinations. Blood drug concentration (measured after 6 and 12 weeks) will provide information on how quickly the drug is cleared from the body, and how this relates to treatment effects and side-effects, to guide future prescribing in people with Parkinson's. Based on knowledge of the average hallucinations scores in previous Parkinson's treatment studies, 306 people will be needed for the study to detect a meaningful treatment effect. The study will run for 4 years and involves a series of linked stages: (1) Trial set up across 20-30 UK centres; (2) Recruitment over 2 years; (3) Completion of follow up; and analysis, publication and dissemination of results.