Injected Apomorphine and Orally Administered Levodopa in Parkinsonism

Abstract

Among 31 patients with parkinsonism three investigations were performed by injecting apomorphine hydrochloride or placebo: (1) to 17 patients with or without orally administered levodopa, (2) to 14 patients receiving levodopa during episodes of tremor, hypokinesia or involuntary movements, and 3 to 10 patients three to 6 times a day for 2 to 43 days. With or without levodopa, apomorphine diminished tremor and rigidity. It decreased bradykinesia in patients receiving levodopa. The respective side effects were not additive: the awakening effect, involuntary movements, and nausea induced by levodopa were antagonized by apomorphine, whereas the sedative effect and the nausea of apomorphine were antagonized by levodopa. The dichotomy between synergistic and antagonistic effects may be explained by the molecule of apomorphine, part of which resembles dopamine and the other resembles phenylethylamine, which can displace neurotransmitters from cellular sites.