Carbimazole is associated with an increased risk of congenital malformations, especially when administered in the first trimester of pregnancy and at high doses. Women of childbearing potential should use effective contraception during treatment with carbimazole.
As you know about 40% of women treated with alemtuzumab go onto to develop hyperthyroidism. The number one drug for controlling thyrotoxicosis is carbimazole. The fact that it is teratogenic is a problem as a lot of women with MS choose to be treated with alemtuzumab so that they can fall pregnant safely off a DMT.
Endocrinologists will have to rely on using propylthiouracil another oral medication that is used to manage hyperthyroidism. Although propylthiouracil may be given in pregnancy it crosses the placenta and in high doses may cause foetal goitre and hypothyroidism, therefore the lowest possible dose should be given and thyroid function monitored every 4-6 weeks to maintain optimum control. Propylthiouracil also transfers to breast milk but this does not necessarily preclude breastfeeding. Neonatal development and infant thyroid function should be closely monitored.
The management of MS gets more complex. I am becoming an endocrinologist in my spare time 😉