Summary of projected decreases in serum concentrations of individual antiseizure medications during pregnancy (if no dose changes are made)

ASM	Decrease in serum concentration	Decrease in serum free (unbound) concentration	Recommendations to perform therapeutic drug monitoring, if available
Phenobarbital	Up to 55%	Up to 50%	Yes
Phenytoin	60 to 70%	20 to 40%	Yes, free concentration
Carbamazepine	0 to 12%	None	Optional
Valproate	Up to 23%	None	Optional, free concentration if done
Oxcarbazepine monohydroxy-derivative (MHD)	36 to 62%	N/A	Yes
Lamotrigine	0.77 of population: 69% decrease 0.23 of population: 17% decrease	N/A	Yes
Gabapentin	Insufficient data	N/A	Yes
Topiramate	Up to 30%	N/A	Yes
Levetiracetam	40 to 60%, with maximal decrease reached in first trimester	N/A	Yes
Zonisamide	Up to 35% but little data	N/A	Yes

ASM: antiseizure medication; N/A: not applicable.

From: Tomson T, Battino D, Bromley R, et al. Management of epilepsy in pregnancy: a report from the International League Against Epilepsy Task Force on Women and Pregnancy. Epileptic Disord 2019; 21:497. Available at: https://onlinelibrary.wiley.com/doi/10.1684/epd.2019.1105. Copyright © 2019 The Authors. Reproduced under the terms of the Creative Commons Attribution SahareAlike License 4.0.

Graphic 126398 Version 2.0