NEW YORK (Reuters Health) – Although promethazine and metoclopramide have similar antiemetic effects in hyperemesis gravidarum, metoclopramide has fewer side effects, according to a study published online April 20 in Obstetrics & Gynecology.

Hyperemesis gravidarum is defined as severe vomiting in pregnancy that requires hospitalization. According to Dr. Peng Chiong Tan and colleagues from the University of Malaysia in Kuala Lumpur, the condition affects up to 2.3% of pregnant women. In 2004, the American College of Obstetricians and Gynecologists recommended that patients with hyperemesis gravidarum receive promethazine or metoclopramide intravenously as a first-line antiemetic therapy.

For their double blind randomized trial, Dr. Tan’s group recruited women hospitalized for the first time in their pregnancies for hyperemesis gravidarum and assigned them to receive either 25 mg promethazine or 10 mg metoclopramide intravenously every 8 hours for 24 hours. There were no significant differences in patient characteristics between the two groups.

A total of 73 and 76 women in the metoclopramide and promethazine groups, respectively, were analyzed. Before the first dose of the study drug and at 8, 16, and 24 hours afterward, the women charted vomiting episodes and marked a nausea visual numerical rating scale.

Primary outcomes over the 24-hour study period were not significantly different in the metoclopramide and promethazine groups. The median number of vomiting episodes was 1 with metoclopramide and 2 with promethazine (range, 0 to 26 in both groups). Well being scores on the visual numerical rating scale (range 1–10, with high scores denoting more severe nausea) were 8 for the metoclopramide group and 7 for the promethazine group. A repeated-measures analysis of variance also showed no difference between the trial arms for nausea visual numerical rating scale scores.

But at the end of the 24-hour main study period, women in the metoclopramide group reported significantly fewer side effects than those on promethazine. For example, 58.6% versus 83.6% described feeling drowsy (p = 0.001), 34.3% versus 71.2% reported dizziness (p < 0.001), and 5.7% versus 19.2% reported dystonia (p = 0.02). The numbers of patients it would be necessary to treat with metoclopramide to prevent one additional bad outcome with promethazine was 3 for dizziness, 5 for drowsiness, and 8 for dystonia. Furthermore, 7 women in the promethazine arm, but none in the metoclopramide arm, curtailed therapy because of adverse events. Difficulty sleeping, dry mouth, diarrhea, headache, palpitations, skin rash were reported in similar proportions across the trial arms. Dr. Tan told Reuters Health by email that to the best of the team’s knowledge, this is the first head to head comparison of these two commonly used drugs in women with hyperemesis gravidarum. “Overall, we feel that metoclopramide is preferred over promethazine for the initial treatment of hospitalized hyperemesis gravidarum as it has less side effects though therapeutic effects are similar,” Dr. Tan said. Obstet Gynecol 2010.