Pharmacotherapy of Emesis
The initial evaluation of the patient with nausea and vomiting should include the onset of symptoms; the severity and duration of symptoms; hydration status; precipitating factors; current medical conditions and medications; and food and infectious contacts. The etiology of the nausea and vomiting should be determined, if possible, so that underlying conditions can be treated specifically. Supportive treatment should be initiated, if needed, including fluid and electrolyte replacement. If the nausea and vomiting is mild and self-limited, antiemetic therapy may not be required. For others, however, the appropriate antiemetic therapy will depend on the patient and the etiology of the nausea and vomiting.
Motion Sickness
1. P.C. is a 27-year-old woman who has no significant medical history, with the exception of moderate dysmenorrhea and motion sickness associated with travel by air. Previously, she has taken dimenhydrinate before airplane trips with moderate success. She is engaged to be married, and she and her fiancé have decided on a week-long Caribbean cruise for their honeymoon. P.C. is concerned that she may also develop sea sickness and that dimenhydrinate may not control her symptoms, particularly in the event of rough weather at sea. Will P.C. be at higher risk for motion sickness?
The symptoms of motion sickness occur in response to an unusual perception of real or apparent motion. In these situations, there is sensory conflict about body position or motion through the visual, vestibular, or body proprioceptors. Acetylcholine is thought to be the primary neurotransmitter involved in signaling the VC, as is histamine, to a lesser extent. Adrenergic stimulation can block this transmission. Symptoms begin with stomach discomfort and progress to salivation changes, sweating, dizziness, lethargy, retching, and emesis. The risk of motion sickness is low in children <2 years of age. The risk is highest in children and adolescents, and higher in females than males. In some individuals, sensitivity to motion sickness diminishes over time. Travel by boat is most likely to cause symptoms; air, car, and train travel is less likely.1,2 Because of P.C.'s history and her travel plans, she is at high risk for recurrence of her motion sickness symptoms.
Nonpharmacologic measures or natural remedies may be useful for reducing motion sickness. These include riding in the middle of the boat or plane where the motion is less dramatic; lying in a semirecumbent position; fixing the vision on the horizon; avoiding reading; and closing the eyes if below deck or in the cabin. Many people recommend keeping active on a ship to “get their sea-legs” faster through habituation. The effectiveness of acupressure at the P6 point of the wrist (about three fingerbreadths above the wrist) is unclear. A controlled-stimulus trial compared two brands of wristbands with placebo; neither band was more effective than placebo in preventing symptoms of motion sickness.3 Studies of ginger preparations also are equivocal. The action of ginger may be of promotion of gastric emptying and not on the vestibular system.4,5
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2. For P.C., what medications are available to prevent and treat motion sickness symptoms?
Anticholinergic agents and antihistamines that cross the blood–brain barrier effectively prevent and treat motion sickness.1,2 In general, these medications are more effective in preventing than treating established symptoms. 5-hydoxytryptamine 3 (5-HT3) receptor antagonists and neurokinin-1 (NK-1) receptor antagonists have not been shown to be effective in preventing motion sickness6,7 and are very costly. Nonsedating antihistamines are not as effective as other antihistamines because they do not sufficiently cross the blood–brain barrier.1 Scopolamine has been well studied for the prevention of motion sickness and is highly effective.8 In a controlled trial, scopolamine was more effective than promethazine and both were more effective than placebo, meclizine, or lorazepam.9 Scopolamine is available as a topical patch, which bypasses the problem of GI symptoms associated with motion sickness. Scopolamine is less likely than dimenhydrinate to effect psychomotor performance.10 Table 7-1 describes medications effective for motion sickness, including the recommended use and the adult doses. The severity of the stimulus is highly dependent on the individual and also varies with the weather and with position in the plane or boat.
Because P.C. is a susceptible individual in a moderate-severe stimulus situation, prevention with a scopolamine patch applied behind the ear every 3 days, starting 6 to 8 hours before departure should be recommended. If she experiences breakthrough symptoms, dimenhydrinate or promethazine can be recommended as well. She should be advised about the potential adverse effects of these agents, which include drowsiness, confusion, and dry mouth.
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