Model-informed Precision Dosing Guidance of Ethosuximide Developed From a Randomized Controlled Clinical Trial of Childhood Absence Epilepsy.

Ethosuximide was identified as the optimal option for new-onset childhood absence epilepsy (CAE) in a randomized, two-phase dose escalation comparative effectiveness trial of ethosuximide, lamotrigine, and valproic acid. However, 47% of ethosuximide initial monotherapy participants experienced short-term treatment failure. This study aimed to characterize the initial monotherapy ethosuximide exposure-response relationship and to propose model-informed precision dosing guidance. Dose titration occurred over a 16-20-week period until patients experienced seizure-freedom or intolerable side effects. Subjects with initial monotherapy failure were randomized to one of the other two medications and dose escalation was repeated. A population PK model was created using plasma concentration data (n=1320), collected at 4 week-intervals from 211 unique participants during both the initial and second monotherapy phases. A logistic regression analysis was performed on the initial monotherapy cohort (n=103) with complete exposure-response data. 84 participants achieved seizure freedom with a wide range of ethosuximide area under the curves (AUC) ranging from 420 to 2420 μg·h/mL. AUC exposure estimates for achieving a 50% and 75% probability of seizure freedom were 1027 and 1489 μg·h/mL, respectively while the corresponding cumulative frequency of intolerable adverse events was 11% and 16%. Monte Carlo Simulation indicated a daily dose of 40 and 55 mg/kg to achieve 50% and 75% probability of seizure freedom in the overall population, respectively. We identified the need for adjusted mg/kg dosing in different body weight cohorts. This ethosuximide proposed model-informed precision dosing guidance to achieve seizure freedom carries promise to optimize initial monotherapy success for patients with CAE.