Motion sickness

Motion sickness is characterized by nausea, excessive salivation, and vomiting, and affected animals may have other signs referable to stimulation of the autonomic nervous system. Animals may yawn, whine, and show signs of uneasiness or apprehension; severely affected ones may also have diarrhea. Motion sickness is usually seen during travel by land, sea, or air, and signs usually disappear when vehicular motion ceases. Many animals, including people, may be affected. The principal causative mechanism involves stimulation of the vestibular apparatus in the inner ear, which has connections to the emetic center in the brain stem. The chemoreceptor trigger zone (CRTZ) and H1-histaminergic receptors are involved in this pathway in dogs, but apparently are less important in cats. Fear of the vehicle may be a contributory factor in dogs and cats, and signs may be seen even in a stationary vehicle.

In some cases, motion sickness can be overcome by conditioning the animal to travel. In others, ataractic and antinausea drugs can be used with good results. Antihistamines (such as diphenhydramine hydrochloride, dimenhydrinate, meclizine, and promethazine hydrochloride) prevent motion sickness, provide sedation, and inhibit drooling.  The centrally acting phenothiazine derivatives (such as triethylperazine, chlorpromazine, prochlorperazine, and acepromazine maleate) have antiemetic as well as sedative effects. Cats have no histamine receptors in the CRTZ; therefore, antihistamines are ineffective in treating motion sickness in this species. Motion sickness in cats probably is best treated with an α-adrenergic antagonist (eg, chlorpromazine) instead of a pure H1-histaminergic antagonist. Phenobarbital and diazepam have been used to produce a general sedative effect. Oral administration of one of these drugs several hours before departure should reduce or eliminate the signs of motion sickness.