Magnesium in pregnancy

Intravenous magnesium infusions may not be as safe in pregnant women as it has been always thought. The FDA recently moved intravenous magnesium from category A into category D (see category definitions below). This came about after the FDA reviewed 18 cases of babies who were born with serious problems after their mothers received intravenous infusions of large amounts of magnesium for 5 to 7 days in order to stop premature labor. The FDA strongly discourages this practice and states that “Administration of magnesium sulfate injection to pregnant women longer than 5-7 days may lead to low calcium levels and bone problems in the developing baby or fetus, including thin bones, called osteopenia, and bone breaks, called fractures.”

However, treatment of choice for eclampsia remains intravenous magnesium. Eclampsia, one of the most serious complications of pregnancy can be treated only with high doses of intravenous magnesium. Without intravenous magnesium eclampsia can lead to epileptic seizures, very high blood pressure, kidney failure and death.

The FDA also recommends that “Magnesium sulfate injection should only be used during pregnancy if clearly needed. If the drug is used during pregnancy, the health care professional should inform the patient of potential harm to the fetus.”

We do treat many patients, including pregnant women, with intravenous infusions of magnesium if they are deficient in magnesium and if their migraines respond to such infusions. Typically, these infusions are given monthly and the amount is only 1 gram, while for preterm labor the dose is 4-6 grams to start and then 2-4 grams an hour as needed. This monthly dose of 1 gram is extremely unlikely to cause any adverse effects. We find that migraines triggered by magnesium deficiency do not respond well to any other treatments and considering the risk of drugs, it is much safer to administer 1 gram of magnesium. This amount of magnesium just corrects the deficiency and does not cause very high magnesium levels, which can be detrimental.

Several other drugs routinely used in pregnancy may also not be as safe as we thought. Acetaminophen (Tylenol) has been considered one of the safest choices. However, recent evidence suggests possible link to attention deficit disorder with hyperactivity (ADHD).

Butalbital, which is an ingredient in the popular headache drugs such as Esgic, Fioricet and Fiorinal is associated with an increased risk of congenital heart defects. Fioricet also contains caffeine, which has negative effects on the fetus and which can cause rebound (medication overuse) headaches.

FDA drug categories in pregnancy

Category A
Adequate and well-controlled studies have failed to demonstrate a risk to the fetus in the first trimester of pregnancy (and there is no evidence of risk in later trimesters).
Example drugs or substances: levothyroxine, folic acid, liothyronine

Category B
Animal reproduction studies have failed to demonstrate a risk to the fetus and there are no adequate and well-controlled studies in pregnant women.
Example drugs: metformin, hydrochlorothiazide, cyclobenzaprine, amoxicillin, pantoprazole

Category C
Animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.
Example drugs: tramadol, gabapentin, amlodipine, trazodone, prednisone

Category D
There is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience or studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.
Example drugs: topiramate (Topamax), divalproex sodium (Depakote), lisinopril, alprazolam, losartan, clonazepam, lorazepam

Category X
Studies in animals or humans have demonstrated fetal abnormalities and/or there is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience, and the risks involved in use of the drug in pregnant women clearly outweigh potential benefits.