Chapter 15: Antiparkinson Drugs

Parkinson's disease represents a progressive neurodegenerative condition stemming from dopamine depletion in the substantia nigra, resulting in the characteristic motor symptoms of tremor, rigidity, akinesia, and postural instability. The pathophysiology involves an imbalance between reduced dopaminergic signaling and unopposed cholinergic activity in the basal ganglia, disrupting normal motor control and movement initiation. Pharmacologic management employs multiple drug classes designed to restore neurochemical balance through different mechanisms. Dopamine replacement therapy using carbidopa-levodopa remains the gold standard, with carbidopa functioning as a peripheral decarboxylase inhibitor to enhance levodopa bioavailability. Dopamine agonists including pramipexole, ropinirole, and rotigotine directly stimulate dopamine receptors and offer alternative therapeutic options. Monoamine oxidase type B inhibitors such as selegiline and rasagiline extend dopamine availability by preventing enzymatic breakdown, while catechol-O-methyltransferase inhibitors including entacapone and tolcapone further prolong dopamine action at the synaptic level. Anticholinergic medications like benztropine counterbalance excessive acetylcholine activity, particularly benefiting tremor symptoms, whereas amantadine provides dopamine modulation through multiple mechanisms. Emerging therapies including pimavanserin address psychiatric complications of Parkinson's disease by modulating serotonin pathways rather than dopamine. Nursing practice requires comprehensive patient assessment encompassing mobility status, swallowing function, cognitive changes, and mood alterations. Critical adverse effects demanding monitoring include orthostatic hypotension, hallucinations, dyskinesias, wearing-off phenomena, and on-off motor fluctuations that complicate long-term therapy. Medication timing relative to meals proves essential since dietary protein competes with levodopa absorption, and nurses must educate patients on fall prevention, medication adherence, and recognition of serious complications like hepatotoxicity and urinary retention.