Abstract Body (Do not enter title and authors here): Objective: While prior studies have examined the clinical risk of arrhythmias associated with lamotrigine (LTG), potentially due to a delay in cardiac conduction, it remains unknown whether this risk of cardiac events translates into an economic outcome. To address this knowledge gap, we conducted a comparative healthcare cost study between patients prescribed LTG and those receiving other commonly used comparator agents.

Methods: We conducted a retrospective cohort study using Merative MarketScan^® Commercial Claims Database (January 2017 through June 2021). The index date was defined as the date of the first prescription of LTG or comparator drugs (lithium, quetiapine, valproate, or risperidone) for a diagnosis of bipolar I disorder. We included adults who were continuously enrolled in the database for both the 6-month pre- and post-index periods. The outcome was all-cause healthcare costs. To assess the impact of LTG on the outcome, we used difference-in-difference (DiD) approach: comparing cost changes from the 6-month pre-index to post-index periods between propensity-score matched LTG and comparator cohorts. The DiD estimate was derived from a generalized linear model (GLM). To assess robustness, we analyzed 6-month post-index costs using a new propensity score–matched cohort adjusted for baseline characteristics.

Results: The matched cohort included 21,128 pairs of patients with well-balanced baseline characteristics, except for geographic region. The median age in both groups was 32 years, and 65% were female. In the LTG group, 6-month healthcare costs decreased by $1,479 (SD $20,073) after the index date, which was less than the $1,740 reduction ($20,082) observed in the control group. However, the DiD estimate from GLM showed that the treatment effect was not statistically significant (β = 261.2, p = 0.181), indicating no significant difference in pre-post healthcare costs between the LTG and matched controls. The result of the secondary analysis was similar to that of the primary analysis, aligning in direction with the main estimates.

Conclusions: The impact of LTG and the control group on healthcare costs was similar. This all-cause cost comparison will be followed by an analysis of cardiovascular healthcare resource utilization and costs to provide further insight into the composite impact of the LTG use on cardiac outcome from the healthcare payer’s perspective.