Chapter 24: Antiparkinsonism Agents

Antiparkinsonism Agents , focusing on Antiparkinsonism Agents, delves into the management of Parkinson disease (PD), a progressive, chronic neurological disorder marked by distinctive motor symptoms such as rhythmic tremors, rigidity, posture changes, and bradykinesia (extreme slowness of intentional movement). The underlying pathology of PD involves the degeneration of inhibitory, dopamine-producing neurons in the substantia nigra. This neuronal loss upsets the chemical balance within the basal ganglia and corpus striatum, allowing excitatory cholinergic (acetylcholine-using) neurons to dominate the inhibitory dopaminergic system, which results in the characteristic manifestations of the disease. Since there is currently no cure to arrest the neuron degeneration, treatment aims to restore this neurotransmitter balance to provide optimal function for as long as possible. Therapeutic drug classes include Dopaminergic Agents and Anticholinergic Agents. Dopaminergics, such as the mainstay drug levodopa (a precursor that crosses the blood-brain barrier and is converted to dopamine), work by either increasing dopamine effects or directly stimulating dopamine receptors. Levodopa is frequently combined with carbidopa to inhibit its peripheral metabolism, allowing higher levels to reach the central nervous system and reducing adverse effects. Other dopaminergics include direct agonists like pramipexole and rotigotine, as well as amantadine. Anticholinergic Agents, including benztropine and trihexyphenidyl, suppress the stimulatory effects of acetylcholine in the brain, often serving as adjunctive treatment or for patients who no longer respond adequately to levodopa. Additionally, Adjunctive Agents are reserved for use in combination with carbidopa-levodopa when responsiveness declines. These include COMT inhibitors (entacapone, tolcapone) and MAO type B inhibitors (rasagiline, selegiline), which prevent the breakdown of dopamine, thereby extending levodopa’s duration of action. Nursing considerations are paramount, emphasizing careful patient monitoring for significant adverse effects—such as CNS changes, cardiovascular issues, and anticholinergic effects like urinary retention and constipation—and providing extensive teaching, especially regarding critical drug interactions, such as the danger of combining dopaminergics with MAOIs or the reduced efficacy of levodopa when excessive Vitamin B6 intake occurs.