D. Dopamine-receptor agonists

This group of anti-Parkinson compounds includes bromocriptine, an ergot derivative, and newer, nonergot drugs, ropinirole, pramipexole, and rotigotine. These agents have durations of action longer than that of levodopa and, thus, have been effective in patients exhibiting fluctuations in their response to levodopa. Initial therapy with the newer drugs is associated particularly with less risk of developing dyskinesias and motor fluctuations when compared to patients started with levodopa therapy. Bromocriptine, pramipexole, and ropinirole are all effective in patients with advanced Parkinson disease complicated by motor fluctuations and dyskinesias. However, these drugs are ineffective in patients who have shown no therapeutic response to levodopa. Apomorphine is also used in severe and advanced stages of the disease as an injectable dopamine agonist to supplement the oral medications commonly prescribed.