An injectable mineral given IV or IM to prevent and stop seizures in preeclampsia and eclampsia, and to replace magnesium when levels are low. Too much causes loss of reflexes, slowed breathing, and heart problems, so reflexes, breathing, urine output, and levels are checked, and IV calcium reverses toxicity.
Magnesium sulfate supplies magnesium, which the body needs for many enzyme reactions and for normal nerve signaling and muscle activity. Where nerves meet muscles, it cuts the amount of acetylcholine, the chemical messenger the nerve releases, which blocks the signal to the muscle. This blocking effect is how it prevents and controls seizures, and it is also said to have a calming effect on the brain. It also widens blood vessels, which causes flushing and sweating at low doses and lowers blood pressure at larger doses.
Given by IV, its anti-seizure effect starts right away and lasts about 30 minutes, while a shot into a muscle starts in about an hour and lasts 3 to 4 hours. The kidneys are the only way the body clears it, so weak kidneys can let it build up to toxic levels. As levels climb too high, reflexes weaken and then disappear, and breathing can stop. Very high levels can also block the heart's electrical signals and can be fatal, and calcium given by IV partly reverses these effects.
Magnesium sulfate injection prevents seizures in preeclampsia, a dangerous rise in blood pressure during pregnancy, and controls the seizures of eclampsia. It also replaces magnesium when blood levels run low, especially when the shortage causes muscle spasms like those seen with low calcium. Low magnesium mainly affects nerves and muscles, causing irritable muscles, twitching, and tremors. Refilling the magnesium in the blood makes these symptoms stop.
It is given by IV or as a shot into a muscle, and in eclampsia the IV route is saved for seizures that threaten life. It can also be added to IV nutrition to correct or prevent low magnesium that develops during that feeding. It should be used in pregnancy only when clearly needed, and its safety and effectiveness for stopping preterm labor have not been established. It is not given for low magnesium unless a blood test has confirmed the shortage.
Flushing and sweating are what people notice first. Most side effects come from too much magnesium: low blood pressure, weak or absent reflexes, muscle weakness, low body temperature, and slowed breathing that can lead to respiratory paralysis and cardiac arrest. The label also warns that giving it for more than 5 to 7 days in pregnancy can weaken the baby's bones, that newborns can be born with magnesium toxicity, and that low calcium can occur.