This is a relatively new approach to augmenting l-dopa therapy. By inhibiting the enzyme, blood concentrations of l-dopa are higher, and more can enter the brain. Studies show a significant improvement in response. The principle of this use is based on the fact that there are cholinergic fibers in the striatum which have opposite effects to those of the dopaminergic neurons. Antagonizing acetylcholine therefore serves to balance the diminished dopaminergic activity seen in Parkinsonism.
Anticholinergic drugs are effective, but basically inferior to l-dopa.
They therefore are used as adjuncts or as the sole therapy early in the disorder. These drugs are also the primary drugs used to treat drug-induced Parkinsonism. The peripheral antimuscarinic actions may be helpful in inhibiting salivation, but undesirable in aggravating urinary retention and constipation. The primary approach to treating Parkinsonism is pharmacotherapy. Surgical lesions in the thalamus relieve some symptoms, but this is seldom done.