Mike C: Hello, I'm Mike Clarke, podcast editor for the Cochrane Library. The Cochrane Pain, Palliative and Supportive Care Group has more than 270 active full reviews in the Cochrane Library. They added to these in May 2022 with a new review of the effects of giving antiemetics to adults receiving intravenous opioids in acute care. We asked lead author, Michael Gottlieb from the Department of Emergency Medicine at Rush University Medical Center in Chicago, USA, to tell us more in this podcast.

Mike G: Pain is a common reason for patients to present to the Emergency Department, or ED. In fact, pain is present in about half to three-quarters of all ED visits. Often, we use opioids such as morphine or hydromorphone to treat the pain but these can cause a variety of side effects, including nausea and vomiting in up to one-third of patients. Some experts have suggested giving an antiemetic before the opioid medication to prevent this, but these drugs also have side effects. Therefore, it's important to know whether antiemetic medications are safe and effective for preventing nausea or vomiting from opioids, and we've found that although they seem safe, they might not be effective.
We investigated whether antiemetics given before opioids reduced the risk of developing nausea or vomiting. We assessed this by looking at both the number of episodes and severity of symptoms, as well as for any adverse events. We had planned to analyze this across different types of antiemetic, but all the studies used the same one, metoclopramide.
We found 3 placebo-controlled randomized trials, consisting of 527 patients in total. One study was conducted in Malaysia, one in New Zealand, and one in Australia. Although all three trials used metoclopramide as the anti-emetic, they tested this for different opioids, including morphine, pethidine and tramadol. 
We judged the overall certainty of the evidence to be low due to small sample sizes and low event rates but, when compared with the placebo, metoclopramide did not reduce nausea, vomiting or the need for rescue medication. There was also no difference in adverse events. 
In summary, giving metoclopramide before an opioid does not appear to reduce the likelihood of the patient developing nausea or vomiting, but also had no impact on adverse events. This suggests that routine metoclopramide before opioids does not appear to benefit patients. However, more data are needed to assess whether there are specific patients who may benefit or whether a benefit may be seen with other anti-emetics.

Mike C: If you would like to learn more about this topic, and to watch for future updates of the review if new data become available, just go to Cochrane Library dot com and search 'antiemetics (without a hyphen) and opioids'.