Perioperative Fluctuations of Lamotrigine Serum Levels: One Risk Factor for Early Postoperative Seizures after Epilepsy Surgery?

Purpose: Insufficient serum levels of antiepileptic drugs are an important risk factor for postoperative seizures. Several possible influencing factors might contribute to a postoperative decrease of serum levels such as anesthetics and postoperative co-medication including steroids, analgetics and drugs for ulcer prophylaxis. Methods: We studied medical records and anesthesia protocols of 20 patients on lamotrigine during epilepsy surgery and evaluated perioperative fluctuations of lamotrigine serum levels. All patients had standardized so-called TIVA (total intravenous anesthesia) without barbiturates, only three patients had additional isoflurane. Results: 16 out of 20 patients had a relevant postoperative decrease of serum levels of more than 20% (mean 47.5%). Six patients had one or more postoperative seizures, in two cases serum levels on the day on which seizures occurred were documented and showed a correlation with the lowest postoperative serum level. The nadir of serum levels was in more than 50% of the patients not in the early postoperative period (POD one and two) but later (between POD 5 and 13). Conclusion: Our retrospective analysis shows a relevant postoperative decrease of lamotrigine serum levels in the majority of our patients. This might be a relevant and evitable co-factor for early postoperative seizures. We hypothesize an influence not only of anesthetics but also of postoperative medication which included in the majority of our patients dexamethasone and ranitidine or a proton pump inhibitor. As a consequence from our data, we recommend frequent postoperative analysis of serum levels, a temporary perioperative dose augmentation should be considered to avoid a relevant postoperative decrease of serum levels with the risk of early postoperative seizures.