Comparison of Benzhexol and Procyclidine for Tremor in Tremor-Predominant Parkinson's Disease

This randomized clinical trial will compare the effectiveness of benzhexol and procyclidine in improving tremor in patients with tremor-predominant Parkinson's disease who are receiving levodopa therapy.

Eligible participants will be adults aged 40 to 70 years with clinically diagnosed Parkinson's disease, predominant tremor at presentation, Hoehn and Yahr stage 1, 2, or 3, and resting tremor while receiving levodopa/carbidopa monotherapy. Participants with cognitive or behavioral abnormalities, lower urinary tract symptoms, benign prostatic hyperplasia, angle-closure glaucoma, or cardiac disease will be excluded.

Participants will be randomly assigned to one of two treatment groups. Group A will receive benzhexol and Group B will receive procyclidine, in addition to their existing levodopa treatment. Benzhexol will be started at 2 mg on the first day, increased to 2 mg twice daily on day 4 and to 2 mg three times daily on day 7, with subsequent dose adjustment according to tremor response and tolerability. Procyclidine will be started at 2.5 mg three times daily on day 1, increased according to the protocol to a maximum of 5 mg three times daily by day 7, with subsequent dose adjustment according to tremor response and tolerability.

Motor symptoms will be assessed using Part III of the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS-III). The primary assessment will focus on the total tremor subset score comprising the following eight items: postural tremor of the right hand, postural tremor of the left hand, rest tremor amplitude of the right upper extremity, rest tremor amplitude of the left upper extremity, rest tremor amplitude of the right lower extremity, rest tremor amplitude of the left lower extremity, rest tremor amplitude of the lip/jaw, and constancy of rest tremor.

Improvement will be assessed as the absolute change in the total tremor subset score from baseline, with the primary comparison made at the 2-week follow-up. The study aims to determine whether benzhexol provides at least similar improvement in tremor compared with procyclidine.

Participants will be assessed at baseline and at 2 weeks, 3 months, and 6 months after treatment initiation. MDS-UPDRS-III assessments will be performed by an independent observer, and adverse effects and tolerability of the study medications will be assessed and documented at follow-up visits.

The planned study enrollment is 88 participants, with 44 participants allocated to each treatment group. The study will be conducted in the Department of Neurology, Mayo Hospital, Lahore.