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Motion Sickness: Comparison of Metoclopramide and Diphenhydramine to Placebo

  • Stephanie Rubio (a1), Lori Weichenthal (a2) and Jim Andrews (a2)

Objectives: This is an evaluation of the efficacy of metoclopramide (MTCP) or diphenhydramine (DPH) to relieve symptoms of motion sickness in patients being transported via ambulance in a mountainous setting.

Methods: This is a prospective, randomized, double-blinded, placebo-controlled study of patients transported by ambulance in the Sierra Nevada mountains of Fresno County. Consenting patients who met the inclusion criteria were asked to rate their motion sickness every five minutes using a visual analog scale (VAS) during transport. If motion sickness occurred, they were randomized to receive MTCP (20 mg IV), DPH (50 mg IV), or placebo (normal saline), and remaining symptoms were recorded every five minutes. If signs and symptoms of motion sickness persisted after 15 minutes, a rescue dose of MTCP was offered.

Results: Twenty-six patients were enrolled in the study. Twenty-two (84.6%) developed motion sickness and were randomized to MTCP, DPH, or placebo. Eight patients received MTCP, seven received DPH, and seven received placebo. The MTCP group showed a statistically significant decrease in the mean VAS score at 15 minutes compared to the DPH and placebo groups. There was no significant difference in the decrease in VAS score between the placebo and the DPH group. Twelve out of 22 patients requested a rescue dose of MTCP after 15 minutes. At 25 minutes, there was no significant difference in the VAS score between the three groups.

Conclusion: During ambulance transport in a mountainous setting, the administration of MTCP is superior to both DPH and placebo in the treatment of motion sickness. Diphenhydramine is not superior to placebo.

Corresponding author
Correspondence: Lori Weichenthal, MD 155 North Fresno Street, Suite 206Fresno, California 93701-2302 USA E-mail:
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Prehospital and Disaster Medicine
  • ISSN: 1049-023X
  • EISSN: 1945-1938
  • URL: /core/journals/prehospital-and-disaster-medicine
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