Irregular gastrointestinal drug absorption in Parkinson's disease
Symptomatic treatment of Parkinson's disease (PD) is based on the dopamine precursor levodopa. Levodopa is only absorbed in the small intestine, where transit time is approximately 3 h and the plasma elimination half-life is short. Therefore, gastric emptying is a major determining factor for onset of symptom relief. Gastric emptying is delayed in PD, thereby causing motor fluctuations such as 'delayed on'. Factors that further slow gastric emptying should be recognised and eliminated if possible. A literature search was performed with the aim to cover the area of irregular gastrointestinal drug absorption in PD. Methods for facilitation of pyloric passage or increase of bioavailability are discussed. Development of new drug formulations and alternative routes of administration is ongoing. Transdermal patches and pumps for subcutaneous or intraduodenal infusions are available for patients with severe fluctuations due to erratic gastric emptying.