Purpose <p>Lacosamide is well known for its additional anti-seizure activity, especially during pregnancy when monotherapy of lamotrigine or levetiracetam fails in people with focal seizures. Pharmacokinetics change during pregnancy and limited results of changes in lacosamide plasma concentrations are available.</p> Methods <p>In this case series, 6 women were retrospectively studied in change of concentration dose ratios (C/D ratios) during pregnancy.</p> Results <p>We found that C/D ratios changed during the trimesters of pregnancy between 48% and 146% compared to baseline values. We couldn’t find a relationship between CD ratios (B=-36, 95%CI= -81-8.5, p-value = 0.10) or RTCs (B = -0.37, 95%CI = -1.3-0.54; p-value = 0.40) during pregnancy and the change in seizure frequency. In future larger datasets are necessary for further recommendations.</p> Conclusion <p>We found that lacosamide concentrations changes during pregnancy, however in this small sample set variations were too high to draw firm conclusions.</p>