Magnesium sulfate fails to relieve cesarean pain.(Obstetrics)

SCOTTSDALE, ARIZ. -- Perioperative use of magnesium sulfate during cesarean delivery did not relieve short- or long-term pain for women in a double-blind, randomized controlled trial of 120 women.

Neither high nor low doses produced any benefit in pain control or satisfaction compared with saline solution in the intent-to-treat analysis.

Other than the expected variation in serum concentrations of magnesium, the only significant differences were slightly greater blood loss and longer time to solid foods for the women given magnesium sulfate, study investigator Everett F. Magann, M.D., reported at the annual meeting of the Central Association of Obstetricians and Gynecologists.

"Given the absence of any apparent analgesic benefit and the apparent increase in blood loss, we do not believe that the perioperative administration is clinically useful," said Dr. Magann, a captain in the U.S. Naval Reserve who currently practices at Naval Medical Center Portsmouth (Va.).

The investigators wanted to test magnesium sulfate because it has been used successfully to control pain from cancer and some surgical procedures in other fields of medicine, according to Dr. Magann. He said they had found one abstract reporting that preeclamptic women undergoing cesarean deliveries had less pain than did matched controls.

"The use of magnesium is very familiar to obstetricians," he said. "It is used in pregnancies complicated by preeclampsia and in pregnancies complicated by preterm labor to delay delivery until corticosteroids have been administered to accelerate fetal lung maturity and lessen neonatal morbidity."

Magnesium is believed to alter pain processing, because it acts as an antagonist to receptors in the spinal cord.