Non-oral dopaminergic therapies for Parkinson's disease: current treatments and the future.

Dysfunction of the gastrointestinal tract has now been recognized to affect all stages of Parkinson's disease (PD). The consequences lead to problems with absorption of oral medication, erratic treatment response, as well as silent aspiration, which is one of the key risk factors in developing pneumonia. The issue is further complicated by other gut abnormalities, such as small intestinal bacterial overgrowth (SIBO) and an altered gut microbiota, which occur in PD with variable frequency. Clinically, these gastrointestinal abnormalities might be associated with symptoms such as nausea, early-morning "off", and frequent motor and non-motor fluctuations. Therefore, non-oral therapies that avoid the gastrointestinal system seem a rational option to overcome the problems of oral therapies in PD. Hence, several non-oral strategies have now been actively investigated and developed. The transdermal rotigotine patch, infusion therapies with apomorphine, intrajejunal levodopa, and the apomorphine pen strategy are currently in clinical use with a few others in development. In this review, we discuss and summarize the most recent developments in this field with a focus on non-oral dopaminergic strategies (excluding surgical interventions such as deep brain stimulation) in development or to be licensed for management of PD.