Metamizole versus ibuprofen after cesarean delivery: no pain difference detected, renal safety uncertain

A quadruple-blind randomized trial compared metamizole with ibuprofen for analgesia after cesarean delivery in women with preeclampsia with severe features. The trial was conducted at a tertiary maternity hospital in northeastern Brazil. It assessed analgesic effectiveness and short-term safety, particularly blood-pressure trajectory and renal function.

Of 74 participants, 38 received oral metamizole 1 g and 36 received ibuprofen 400 mg every 6 hours for up to 5 days. Intravenous tramadol was available for rescue analgesia. The co-primary outcomes were postoperative pain category on the visual analogue scale and acute kidney injury.

Key findings

• The distribution of pain categories did not differ between groups on day 1 (exact P=.45) or day 2 (exact P=.55).
• On day 1, rescue analgesia was required by 18.4% of participants receiving metamizole versus 38.9% receiving ibuprofen; the risk difference was −20.5 percentage points (95% confidence interval −39.1 to 0.1).
• Acute kidney injury occurred in 3 of 38 women (7.9%) versus 1 of 36 (2.8%); the risk ratio was 2.84 (95% confidence interval 0.31–26.08; Fisher P=.62).
• No group-by-time interaction was detected for systolic or diastolic blood pressure. Severe hypertensive episodes were rare in both groups.

Limitations: the trial was not designed to establish equivalence or non-inferiority. The acute kidney injury estimate was highly imprecise; comparative renal safety remains uncertain and requires adequately powered studies.