A 64-year-old man comes to the office due to slowing of his movements and gait instability that has been the cause of several recent falls. The patient was diagnosed with Parkinson disease a year ago. On examination, there is a resting tremor involving the right hand and rigidity during passive flexion and extension of the right upper limb. The patient is started on therapy with pramipexole. Which of the following best describes the mechanism of action of this medication?

Question

A 64-year-old man comes to the office due to slowing of his movements and gait instability that has been the cause of several recent falls.  The patient was diagnosed with Parkinson disease a year ago.  On examination, there is a resting tremor involving the right hand and rigidity during passive flexion and extension of the right upper limb.  The patient is started on therapy with pramipexole.  Which of the following best describes the mechanism of action of this medication?

Quizplus · Accepted Answer

11ec160b_3c18_00d8_9249_855015835e64_MD0001_00 Dopamine agonists have a chemical structure similar to the neurotransmitter dopamine and directly stimulate dopamine receptors. They do not have to be metabolized to be active. There are 2 classes of dopamine agonists: Dopamine agonists have an important role in the treatment of Parkinson disease (PD) as these medications have a long half-life and can delay the need to start levodopa, thereby postponing the development of motor fluctuations until later in the disease course. Bromocriptine also treats hyperprolactinemia. (Choice A) Selegiline is used to delay the clinical progression of PD via inhibition of monoamine oxidase-B (MAO-B) in the brain, resulting in decreased central dopamine degradation. (Choice C) Amantadine exerts several effects with regard to PD. As an indirect and direct dopaminergic agent, it alleviates some of the motor symptoms of PD by enhancing the effects of endogenous dopamine. It is thought also to have some anticholinergic properties, which reduce tremors. (Choice D) Both catechol-O-methyltransferase (COMT) inhibitors (eg, entacapone, tolcapone) and dopa decarboxylase inhibitors (eg, carbidopa) decrease the breakdown of levodopa in peripheral tissues and increase the amount of levodopa available to cross the blood-brain barrier. (Choice E) Anticholinergics, such as trihexyphenidyl and benztropine, inhibit central muscarinic receptors. These drugs are sometimes used to treat patients with drug-induced parkinsonism and those with tremor as the predominant symptom of idiopathic PD. Educational objective: Dopamine agonists have a chemical structure similar to the neurotransmitter dopamine and directly stimulate dopamine receptors. The 2 classes of dopamine agonists are ergot compounds (eg, bromocriptine) and nonergot compounds (eg, pramipexole, ropinirole). __________ References: Current pharmacotherapeutic treatment options in Parkinson's disease. (http://www.ncbi.nlm.nih.gov/pubmed/17586328) Parkinson's disease: diagnosis and treatment. (http://www.ncbi.nlm.nih.gov/pubmed/17186710)

A 64-Year-Old Man Comes to the Office Due to Slowing