Dexamethasone did not beat ondansetron after caesarean, and did not spare opioids either

Design

Prospective randomised double-blinded controlled trial

Population

95 women completing caesarean delivery under spinal anaesthesia with 150 micrograms intrathecal morphine on an enhanced recovery protocol

Primary outcome

Total medications given in 24 hours for nausea and vomiting, pain or pruritus

Effect

Ondansetron 0.23 (95% CI 0.11-0.35) vs dexamethasone 0.40 (95% CI 0.20-0.61) medications per patient per 24 hours, P = .337; no difference in pain, nausea or pruritus scores

One hundred women having caesarean delivery under spinal anaesthesia with 150 micrograms of morphine, on an enhanced recovery protocol with scheduled non-opioid analgesia, were randomised double-blind to dexamethasone 8 mg or ondansetron 4 mg. Ninety-five completed. The outcome was the total number of medications given in the first 24 hours for nausea and vomiting, pain or pruritus - a composite chosen to capture the whole burden of rescue treatment rather than one symptom.

There was no difference: 0.23 medications per patient per 24 hours (95% CI 0.11-0.35) with ondansetron and 0.40 (95% CI 0.20-0.61) with dexamethasone, P = .337. Supplemental analgesia, pain scores, nausea scores and pruritus scores were all statistically indistinguishable across the 24 hours.

The hypothesis being tested was that dexamethasone should be preferred because earlier work showed it reduces analgesic use as well as nausea - a dual benefit. That did not appear here, and the authors offer the likely explanation themselves: with an enhanced recovery protocol running and intrathecal morphine on board, pain scores and breakthrough rates were already low. There was very little left for a second agent to improve. That is a useful negative for anyone building a caesarean pathway: once the multimodal scaffolding is in place, the choice between these two antiemetics stops carrying the analgesic argument, and can be made on cost, glycaemic considerations and what is in the drug cupboard.

• Choose between dexamethasone and ondansetron on cost, availability and patient factors, not on an opioid-sparing claim
• Check the glucose implications of dexamethasone in women with gestational diabetes before making it the default
• The comparison holds only where intrathecal morphine and scheduled non-opioid analgesia are already in use
• Record which agent was given; the trial's rescue rates are only interpretable alongside the background protocol
• Both agents remain effective prophylaxis - this was a comparison, not a placebo trial

Why it matters

The argument for making dexamethasone first line rested on an analgesic bonus, and in a modern caesarean pathway it did not materialise.

Don't overread it

A null result in 95 patients is not equivalence, and the low background rescue rates left little room to detect a difference.

The statistics, in plain English

The point estimates run in opposite directions to the hypothesis - dexamethasone patients needed slightly more rescue medication, not less - but the confidence intervals overlap heavily and 95 patients is too few to separate them. A P value of .337 here means no difference was detected, not that the agents are equivalent; an equivalence claim requires a pre-specified margin and a much larger trial. The more important caveat is the setting. Rescue medication rates of about 0.2 to 0.4 doses per patient per day leave almost no room for improvement, so this trial had little capacity to show a benefit from either drug even if one existed.

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