Impact of residual drug in the pharynx on the delayed‐on phenomenon in Parkinson's disease patients

Background and Objective: The delayed-on phenomenon (DOP) related to levodopa treatment frequently disturbs quality of life in advanced-stage Parkinson's disease (PD) patients. The objective of this study was to explore the impact of swallowing dysfunction on the development of DOP. Methods: Swallowing function was investigated by endoscopic evaluation in 11 PD patients with the DOP and 9 PD patients without the DOP during the on phase. Residual drug in the pharynx after taking the drug in tablet, capsule, and powder forms was also observed. Results: Residual drug was seen in the pharynx in six cases (30.0%). Pooling of saliva, delayed swallowing reflex, and residual drug were more frequent in the DOP group than in the group without the DOP (P < 0.05). The odds ratios for residual drug in the pharynx, pooling of saliva, and delayed swallowing reflex for the DOP were 42.7 (95% confidence interval, 1.89-962.9), 14.0 (95% confidence interval, 1.25-156.6), and 15.8 (95% confidence interval, 1.75-141.4), respectively. Conclusions: These results suggest that swallowing dysfunction leading to residual antiparkinsonian drug in the pharynx has substantial impacts on the DOP in PD patients.