36. A 6-year-old boy is brought to the office by his mother due to difficulty with his behavior in school. She says that his teacher is concerned that he does not pay attention in class and his grades are dropping to the point he may need medication to help him focus. The patient's mother has noticed that at home he seems to stare into space for several seconds, multiple times throughout the day. This occurs even when he is watching his favorite television show, and he seems to ignore her when she calls his name. The patient has no previous medical problems and takes no medications. He has an older brother with attention-deficit hyperactivity disorder and an aunt with epilepsy. Which of the following is the most appropriate pharmacotherapy for this patient?

43. A 64-year-old man comes to the office due to slowing of his movements and gait instability that has contributed to several recent falls. The patient was diagnosed with Parkinson disease a year ago. On physical 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?

99