Not surprisingly, none of the new migraine drugs have been tested in pregnant women. No new drug for any indication is ever tested for its safety in human pregnancy. They are always tested in pregnant animals, which helps weed out most drugs that are clearly dangerous. It takes decades to learn if a drug is safe. This happens through an accumulation of anecdotal reports and pregnancy registries that are usually run by drug manufacturers.
Erenumab (Aimovig) was the first CGRP monoclonal antibody to be approved for the preventive treatment of migraines four years ago. It was tested in pregnant monkeys who were given 50 times higher doses (by weight) than the FDA-approved dose for humans. Even though some of the medicine crossed the placenta into baby monkeys, they had no developmental problems.
In the current issue of Headache, University of Texas doctors published a report of a woman who continued to inject herself with erenumab throughout the duration of her pregnancy. She tried to stop the drug before planning to get pregnant but her severe migraines recurred. Her baby was born healthy and had normal development by the last evaluation at 6 months of age.
This case report is the first very small but important step in the process of evaluating the safety of erenumab in pregnancy.
In humans, the transfer of antibodies, which are large molecules, across the placenta is very limited before the 16th week of pregnancy and increases after the 22nd week. We still recommend stopping the drug about five months before a pregnancy is planned. If a woman, however, does get pregnant, intentionally or not, the risk of complications is low if erenumab is stopped within the first three months of pregnancy. This also applies to all other monoclonal antibodies in general and specifically other migraine drugs – galcanezumab (Emgality), fremanezumab (Ajovy ), and eptinezumab (Vyepti).
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