Comparison of effectiveness of trihexyphenidyl and levodopa on motor symptoms in Parkinson's disease

Despite anti-cholinergics being the oldest type of medication used for the treatment of Parkinson's disease (PD), the mechanism of action and exact benefit is unclear. This study compared the effectiveness of trihexyphenidyl (THP) and levodopa (LD) on motor symptoms in patients with PD. Patients with PD who are currently taking or had taken THP were recruited. UPDRS-III was done following overnight medication OFF state and 30 min, 60 min, 90 min, and 120 min after THP (4 mg). After a forty-eight-hour interval, UPDRS-III was assessed one hour after Levodopa/carbidopa (200/50 mg) in an overnight OFF state. Twenty patients with a mean age of 57.9 +/- 7.8 years and mean duration of illness of 5.1 +/- 3.6 years were recruited. UPDRS-III score reduction (%) with THP was maximum in the tremor sub-score (53.8 +/- 22.8) and was significantly better compared to improvement in total-UPDRS-III (27.0 +/- 14.7), bradykinesia-UPDRS-III (22.2 +/- 27.2), rigidity-UPDRS-III (29.5 +/- 28.0) and axial-UPDRS-III (8.1 +/- 13.3) sub-score. In comparison, respective LD improvement was 67.1 +/- 22.9 (tremor-UPDRS-III), 61.3 +/- 14.4 (total-UPDRS-III), 67.9 +/- 32.1 (bradykinesia-UPDRS-III), 65.3 +/- 25.5 (rigidity-UPDRS-III) and 50.7 +/- 16.0 (axial-UPDRS-III). Improvement (%) in tre-UPDRS-III post-THP was comparable to that of post-LD (53.8 +/- 22.8 vs. 67.1 +/- 22.9,p = 0.057). Those with same or better tremor response with THP had significantly milder baseline tremor severity than those who had better response with LD (tre-UPDRS-III-OFF, 10.0 +/- 2.8 vs. 5.8 +/- 4.0,p = 0.013). Both THP and LD showed significant improvement in UPDRS-III. With THP, the maximum degree of improvement was in the tremor sub-score and not significantly different to that obtained by LD. Those with better tremor response on THP had milder tremor severity.